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    10 March 2024, Volume 43 Issue 3
    Distribution characteristics and influencing factors of soil bulk density at different soil layers in typical small watershed in loess region of western Shanxi Province.
    WANG Simin, ZHANG Hongli, ZHANG Hengshuo, ZUO Qilin, ZHA Tonggang
    2024, 43(3):  609-615.  doi:10.13292/j.1000-4890.202403.039
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    To understand the distribution characteristics and influencing factors of soil bulk density across different soil layers in the loess region, we measured soil bulk density at 0-20, 20-40, 40-60, 60-80, and 80-100 cm layers in 98 locations in Caijiachuan watershed in the loess region of western Shanxi. We analyzed the distribution characteristics, the main influencing factors of each soil layer and their contribution rates to soil bulk density by using classical statistics and geostatistics methods. The results showed that: (1) Soil bulk density ranged from 0.79-1.78 g·cm-3, and increased with increasing soil depth in the 0-100 cm depth. The variation of soil bulk density decreased with increasing soil depth. (2) Gaussian model was the best fitting model for soil bulk density at 0-40 cm layer, while exponential model was the best fitting model at 40-100 cm layer. The spatial dependence of soil bulk density decreased with increasing soil depth, showing strong, moderate and weak spatial dependence at 0-20, 20-60 and 60-100 cm layers, respectively. (3) Soil bulk density at 0-40 cm layer was mainly affected by vegetation and soil factors, while that at 40-100 cm soil layer was mainly affected by elevation and soil factors, suggesting that the effects of vegetation restoration on soil bulk density were mainly concentrated in the surface layer. Our results provide important reference for in-depth understanding of regional soil bulk density distribution under the vegetation restoration and scientific assessment of regional ecological benefits and ecological services of vegetation restoration.

    Soil nutrients and enzyme activities in different types of forest plantations in karst degraded mountainous sites.
    2024, 43(3):  616-622.  doi:10.13292/j.1000-4890.202403.035
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    Artificial vegetation restoration is one of the significant ways of ecological restoration in degraded karst mountainous areas. We investigated soil nutrient contents and soil enzyme activities and their correlations across three types of forest plantations, including Cupressus duclouxina forest, Robinia pseudoacacia forest, and C. duclouxina-R. pseudoacacia mixed forest, with unplanted land (control). We aimed to provide a reference basis for selecting suitable planting species and methods to improve soil quality in this region. The results showed that: (1) soils of all four vegetation types were alkaline, and soil pH of plantations was significantly lower than that of the unplanted land. The contents of organic matter, total nitrogen, alkali-hydrolyzed nitrogen, and available phosphorus in the soil of plantations were significantly higher than that of the unplanted land, while the contents of total potassium and available potassium were significantly lower than that of unplanted land. (2) Except for alkaline phosphatase, the activities of other four enzymes were the highest in C. duclouxina-R. pseudoacacia mixed forest. The activities of urease, alkaline phosphatase, and catalase in plantations were higher than those in the unplanted land. (3) The main factors influenced by soil nutrients were different for urease, polyphenol oxidase, sucrase, and alkaline phosphatase, while the correlation between peroxidase activity and nutrient indicators was not significant. (4) Results of redundancy analysis showed that soil total nitrogen and phosphorus contents had significant effects on soil enzyme activities in different types of plantations, which could explain 60.7% of the variation of enzyme activities. The cumulative contribution rate of variance of enzyme activity and nutrient characteristic relationship was 78.8%. Artificial vegetation restoration in degraded karst mountainous sites could improve soil nutrient contents and enzyme activities, thereby improving soil quality, and then lay the foundation for further improving the service functions and stability of plantation ecosystems and promoting the quality of regional ecological environment. 

    Characteristics of topsoil phosphorus fractions along a chronosequence of Cryptomeria japonica var. sinensis plantations in the rainy area of western China.
    2024, 43(3):  623-632.  doi:10.13292/j.1000-4890.202403.031
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    Phosphorus (P) is one of the essential nutrients limiting plant productivity. However, how stand age affects soil P fractions remains poorly understood. Here, topsoil samples (0-20 cm) were collected from Cryptomeria japonica plantations with seven stand ages (6, 12, 23, 27, 32, 46, 52 years old) in the Hongya Forest Farm in the rainy area of western China in Sichuan basin. Soil P fractions were measured by Hedley P classification method. The results showed that soil total P concents ranged from 231.93 to 370.27 mg·kg-1, and were the lowest at young age (6 years old) and the highest at middle-aged forest (12 years old). The contents of soil total inorganic P and total organic P first increased and then decreased and increased respectively with increasing stand age. The proportion of total inorganic P to total P decreased with increasing stand age, while the pattern for total organic P was opposite. The contents of labile inorganic P, labile organic P and moderately labile organic P generally increased with increasing stand age, which may be correlated with the decrease of pH and the increase of organic carbon content. Moderately labile inorganic P fractions of middle-aged (12 years old) and mature (32 years old) plantations were significantly higher than those of other stand ages. Soil non-labile P fraction first increased and then decreased with increasing stand age, with the increase in soil bulk density and the decrease in soil water content as main reasons. Results of multiple linear regression model and Pearson correlation analysis showed that labile inorganic P did not correlate with stand ages. Moderately labile organic P, which affects labile inorganic P, could increase with increasing stand age. The increase of moderately labile organic P with increasing stand age could positively affect the production of labile inorganic P. Our results indicated that topsoil P fractions varied with stand ages. These findings can help propose solutions to the problems of soil P at corresponding stand ages and provide  theoretical basis for improving the quality and efficiency and maintaining soil fertility of Cryptomeria japonica plantations.

    Planting Cinnamomum camphora can effectively mitigate soil acidity and improve soil nutrients in acid rain area of Chongqing.
    FENG Yongxia, CHEN Ruisi, NI Xiuya, SHANG He, CHEN Zhan
    2024, 43(3):  633-643.  doi:10.13292/j.1000-4890.202403.020
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    Pinus massoniana is one of the main afforestation species in southwest China, which is sensitive to acid deposition. To cope with acid deposition, stand transformation is often carried out in coniferous forests that have been seriously affected. In this study, we explored the effects of transformation of P. massoniana pure plantation on soil acidification and nutrients by comparing P. massoniana-C. camphora mixed plantation, C. camphora pure plantation, and P. massoniana pure plantation in Tieshanping of Chongqing. Soil samples of humus (Ah) and leachate (E) horizons were collected in different seasons. The results showed that: (1) Forest type had significant effects on soil properties in Ah horizon (P<0.05). Soil nutrient concentrations in Ah horizon were significantly higher than those in E horizon. Soil properties in both horizons varied greatly across seasons (P<0.05). (2) After the transformation of P. massoniana pure plantation, soil pH in Ah horizon was in order of P. massoniana pure plantation < P. massoniana-C. camphora mixed plantation < C. camphora pure plantation. Soil NH4+∶NO3- ratio was significantly reduced after the transformation of P. massoniana pure plantation, which could alleviate soil acidification. (3) Soil organic carbon and total nitrogen concentrations were significantly reduced after the transformation of P. massoniana pure plantation, while soil total phosphorus and total potassium concentrations were significantly increased (P<0.05), which could provide more phosphorus and potassium and thus alleviate the phosphorus and potassium limitation on plant growth in the acidic soils. (4) The comprehensive soil fertility index evaluated by the fuzzy comprehensive method was 0.585-0.664. Our results suggested that the transformation of the P. massoniana pure plantation into P. massoniana-C. camphora mixed plantation and C. camphora pure plantation could improve soil fertility.

    Effects of AMF and phosphorus application on microbial biomass and enzyme activities in oat soil under drought stress.
    ZHANG Bin, LYU Yufeng, LI Li, FENG Meichen, WANG Chao, SONG Xiaoyan, YANG Wude, ZHANG Meijun
    2024, 43(3):  644-655.  doi:10.13292/j.1000-4890.202403.034
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    The objectives were to investigate the effects of applying AMF and phosphorus on AMF infection of oat roots, soil microbial biomass, soil enzyme activity, as well as oat yield under drought stress, so as to develop AMF and phosphorus application guidelines for growing oat under drought. The experiment was conducted in pots for a total of 12 treatments, consisted of two levels of water supply, normal water supply (75% soil relative water content, W1) and drought stress (55% soil relative water content, W2), three levels of phosphorus supplement, 0, 20, and 40 mg·kg-1 (P0, P1, P2), and two levels of AMF, inoculated (AMF) and not inoculated (NAMF). Root and soil samples were collected at the jointing, filling, and maturity stages to determine the AMF infection rate of oat roots, the soil MBC, MBN, and MBP, the soil sucrase, urease, and alkaline phosphatase activities. Oat yield was determined at maturity stage. The results showed that significant effects of soil water content, phosphorus, and AMF treatment were found on these indicators. Significant interactions among three factors were found on soil MBN  and soil sucrose activities. Under drought stress, compared with non-inoculated AMF, inoculated AMF significantly increased these indicators. Compared to P0, the AMF infection rate, the soil MBC, MBN, and MBP, the soil sucrase, urease, and alkaline phosphatase activities and yield significantly increased by 13.21%, 52.26%, 47.07%, 88.94%, 23.15%, 15.44%, 11.15% and 17.16% (the maximum value) with P1 application in oat growth period, respectively. However, these indicators tended to be reduced with further increasing of phosphorus application (P2). Therefore, AMF inoculation and a moderate application of phosphorus were effective ways to increase the  soil MBC, MBN and MBP, improve the activities of soil sucrase, urease and alkaline phosphatase, and increase oat yield under drought stress; however, the oat yield did not reach the level in normal water supply without AMF inoculation.

    Effects of organic fertilizer and intercropping on soil microbial characteristics and yield and quality of red pitaya in dry-hot region.
    LI Yilin, LI Kun, LI Jiancha, PAN Zhixian, SHI Liangtao, LIU Xiaogang, FANG Haidong, YUE Xuewen
    2024, 43(3):  656-664.  doi:10.13292/j.1000-4890.202403.013
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    The objective of this study was to investigate the advantages of applying organic fertilizer and intercropping on the planting of red pitaya (Hylocereus costaricensis cv. ‘Tainong No. 2’). A field experiment was carried out to examine the effects of organic fertilizer application rate (F0: 0 t·hm-2 and F20: 20 t·hm-2) and intercropping method \[MP: monoculture pitaya, IP: pitaya intercropping peanut (Arachis hypogaea) and IS: pitaya intercropping soybean (Glycine max)\] on soil microbial abundance, soil microbial biomass and soil enzyme activity, as well as the yield and quality in red pitaya orchard in a dry-hot region. The relationship between the yield and quality of red pitaya and soil microbial characteristics were also analyzed. The results showed that compared with F0 treatment, F20 treatment significantly increased the abundance of soil bacteria, fungi, actinomycetes and microbial biomass carbon, nitrogen and phosphorus, enhanced the activities of soil invertase, urease, acid phosphatase and catalase, and improved the yield and quality of red pitaya. Compared with MP treatment, IP and IS treatment significantly increased soil microbial abundance, microbial biomass nitrogen and the activities of invertase and urease under F0 and F20 conditions; while IP and IS treatments significantly increased soil microbial biomass carbon, phosphorus and acid phosphatase activity only under F20 condition. Intercropping significantly increased the fruit yield of red pitaya. IP and IS treatment increased yield by 48.48% and 42.20% under F0 condition, and increased by 25.37% and 29.82% under F20 condition, respectively, when compared with MP treatment. IP and IS treatments significantly increased soluble sugar and vitamin C content with F0 conditions, but significantly increased vitamin C, soluble solids and protein content with F20 conditions. Yield and quality of red pitaya were significantly positively correlated with soil microbial abundance, soil microbial biomass, and soil enzyme activity. The correlation between soluble sugar content and soil catalase activity was not significant. Therefore, the application of organic fertilizer and intercropping peanut or soybean can enhance soil microbial activity, thus improving the yield and quality of red pitaya in dry-hot region.

    Effect of bioorganic fertilizer on soil quality and yield of continuous cropping sugar beet under reduced chemical fertilizer application.
    TIAN Lu, SU Wenbin, GUO Xiaoxia, HUANG Chunyan, JIAN Caiyuan, ZHANG Peng, LI Zhi, HAN Kang
    2024, 43(3):  665-674.  doi:10.13292/j.1000-4890.202403.044
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    We explored the effects of different fertilization treatments on soil structure, nutrient characteristics, biological characteristics and yield of continuous cropping sugar beet, with the aim to screen out the best application amount of bioorganic fertilizer. With the conventional fertilization (900 kg·hm-2 chemical fertilizer) as the control (CK), we set up bioorganic fertilizer treatments (BOF1: 1500 kg·hm-2; BOF2: 3000 kg·hm-2; BOF3: 4500 kg·hm-2; BOF4: 6000 kg·hm-2; BOF5: 7500 kg·hm-2) on the basis of reducing 300 kg·hm-2 chemical fertilizer. The results showed that the effects of BOF1 on soil quality indices were not significant. The BOF2 significantly increased the content of soil organic matter and available potassium. The BOF3 significantly reduced soil bulk density by 5.11%, significantly increased soil total porosity by 5.92%, soil organic matter by 14.07%, soil alkaline nitrogen by 18.35%, soil available phosphorus by 3.59%, and soil available potassium by 14.61%. Treatments BOF4 and BOF5 had similar effects on soil quality and beet yield. BOF4 and BOF5 significantly reduced soil bulk density by 9.33% and 9.65%, significantly increased soil porosity by 10.82% and 11.19%, soil organic matter by 27.22% and 27.78%, soil alkaline nitrogen by 31.62% and 35.42%, soil available phosphorus by 44.10% and 54.87%, soil available potassium by 22.93% and 30.03%, respectively. Both treatments significantly increased soil microbial biomass carbon by 22.78%-44.19% and 23.81%-60.17%, microbial biomass nitrogen by 2.45%-37.64% and 16.74%-43.56%, invertase activity by 26.03%-38.61% and 29.27%-44.71%, urease activity by 42.72%-63.20% and 51.59%-69.89%, alkaline phosphatase activity by 3.59%-33.44% and 29.60%-38.62%. There were no significant differences in each soil quality index between these two treatments. Compared with CK, the yield of BOF2, BOF3, BOF4 and BOF5 increased by 5.69%, 11.82%, 22.29%, and 11.95%, respectively. The beet yield of treatment BOF4 was significantly higher than that of BOF2, BOF3, and BOF5. Treatment BOF4 increased the economic benefits of continuous cropping sugar beet by 12.79%. In all, the application of 6000 kg·hm-2 bioorganic fertilizer can achieve the synergetic improvement of soil quality, yield and economic benefits of continuous cropping sugar beet.

    Relationship between forest gap characteristics and woody species diversity in a subtropical forest in Jinzhong Mountain.
    YANG Yuanzheng, MENG Zhouju, SU Hongxin, WANG Jiali, CAI Wenhua, YANG Jian, ZU Jiaxing
    2024, 43(3):  675-681.  doi:10.13292/j.1000-4890.202403.019
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    Studies on the relationship between forest gap spatial pattern and understory woody species diversity are of great significance for understanding species coexistence, biodiversity maintenance and sustainable development of forest ecosystems. In this study, we used the airborne Lidar to collect cloud data from a 24 hm2 permanent forest dynamic monitoring plot in Jinzhong Mountain Nature Reserve of Guangxi, extracted forest gaps, and calculated shape complexity index of each forest gap by R programming language. Correlation analysis was conducted to quantify the relationship between forest gap characteristics and understory woody species diversity. The results showed that the forest gap rate in the study area was 6.16%, the gap density was 15.5·hm-2, the average gap area was 39.72 m2, and the gaps were mainly small and middle sized. The spatial distribution pattern of forest gaps had topographic differentiation, mostly distributed in low altitude and gentle slope areas. The gap shape complexity index was positively correlated with Shannon index and species richness index, which was more obvious in low altitude and steep slope areas. This study revealed the characteristics of plant regeneration in the forest gaps of subtropical forests, which has a certain guiding role for regional biodiversity conservation.

    Microclimate characteristics of two treeline ecotones and their different habitats in Segera, southeast Tibet.
    CHEN Wensheng, Ding Huihui, LI Jiangrong, FU Fangwei, LI Yueyao, XIAO Siying
    2024, 43(3):  682-693.  doi:10.13292/j.1000-4890.202403.001
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    This work described the microclimate characteristics of Sygera alpine treeline ecotones, and provided basic data for further study of alpine treeline maintenance mechanisms. Based on the data of automatic weather stations in two treeline ecotones (Abies georgei  var. smithii treeline and Juniperus saltuaria treeline) and the observations of temperature and humidity of air and soil in different habitats of both ecotones in the Sygera Mountain during 2018-2020, we analyzed the microclimatic characteristics of treeline ecotones and the variation characteristics of hydrothermal conditions of the three habitats (under forest, shrub, and forest gap). In both ecotones, mean temperature of the warmest month was 8.71-9.32 ℃. The mean temperature for the coldest month ranged from -7.23 to -9.08 ℃. The annual mean temperature was 0.55-0.88 ℃. The annual temperature difference was 15.95-18.40 ℃. The annual biological temperature was 2.79-3.33 ℃. The warm index was 9.15-12.94 ℃·month-1 and the cold index ranged from -60.22 to -64.98 ℃·month-1. The mean temperature and length of the growing season defined by air temperature were 7.45-8.31 ℃ and 106-136 days, while those defined by 10 cm soil temperature were 6.06-7.01 ℃ and 120-141 days, respectively. Air temperature and humidity in the different habitats of the two ecotones were similar, whereas soil temperature and moisture were highest in the forest gap, with large daily amplitude of soil temperature. Soil temperature in the forest was lower than that of the other habitats, with a “cool foot” effect. The growing season defined by soil temperature lagged behind that defined by air temperature by about one month. The average air temperature, average soil temperature, and soil water content of the forest gaps were higher. The freezing injury events in the forest gaps and shrubs were frequent, strong, and lasting. The differences in microclimate characteristics among different habitats in the treeline ecotones of Sygera Mountain were mainly reflected in soil temperature, growing season temperature, and occurrence of freezing injury events in the growing season.

    Comparative study on water sources of Platycladus orientalis and Ulmus pumila based on hydrogen and oxygen stable isotope tracing.
    LIU Zechen, ZHANG Mingjun, ZHANG Yu, YANG Ye, TIAN Yuanyuan, ZHONG Xiaofei, GU Lailei
    2024, 43(3):  694-700.  doi:10.13292/j.1000-4890.202403.025
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    Clarifying water sources and competition between evergreen and deciduous trees can provide a theoretical basis for the selection and planting methods of tree species during ecological restoration. We measured the ratio of hydrogen-oxygen stable isotopes of soil, precipitation, and xylem of Platycladus orientalis and Ulmus pumila in the Nanshan Greening Engineering Area of Lanzhou. The characteristics of soil water utilization in different depths were analyzed by MixSIAR and proportional similarity index. The results showed that except for July and October, deep (70-100 cm) soil water was the main water source of P. orientalis and U. pumila, with a contribution rate of 55.82% and 58.90%, respectively. In July, both species absorbed shallow (0-20 cm) soil water, with a contribution rate of more than 90%. In October, P. orientalis absorbed middle-layer (20-70 cm) soil water, while U. pumila used both middle-layer (20-70 cm) and deep (70-100 cm) soil water. In summary, P. orientalis and U. pumila do not compete for water in the growing season except July. They can be planted simultaneously in the same habitat.

    Photosynthetic characteristics of Sinojackia huangmeiensis, a species with extremely small population.
    WANG Shitong, SONG Shuaishuai, LI Jiehua, YANG Teng, HE Yiqin, WEI Xinzeng, JIANG Mingxi
    2024, 43(3):  701-708.  doi:10.13292/j.1000-4890.202403.040
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    Sinojackia huangmeiensis, an endemic species with extremely small population in China, was listed as one of the national key protected wild plants. To investigate the response and acclimation of S. huangmeiensis to different light environments, we selected plants in three habitats (gap, understory, and full sunlight habitats), and compared leaf phenotypic traits, photosynthetic characteristics and chlorophyll fluorescence parameters in different habitats. Compared to the full sunlight habitat, specific leaf area (SLA) of S. huangmeiensis was significantly higher, while leaf thickness (LT) and dry matter content (LDMC) were significantly lower in gap and understory habitats. The maximum net photosynthetic rate (Pmax) and light saturation point (LSP) were the highest in the full sunlight habitat, while light compensation point (LCP) and dark respiration rate (Rd) were the lowest in the understory habitat. The electron transport rate (ETR), the effective PSⅡ quantum yield \[Y(II)\], photochemical quenching (qP) and non-photochemical quenching (NPQ) in gap and full sunlight habitats were higher than those in the understory habitat. Our results suggested that S. huangmeiensis can acclimate to the low light environment by reducing LCP, Rd and NPQ, and acclimate to the high light environment by increasing LT, LDMC, LSP and NPQ. Additionally, S. huangmeiensis showed strong acclimation to different habitats, which was of great importance for population regeneration and maintenance, and thus provided new insights for artificial introduction.

    Effects of light intensity on growth and photosynthetic characteristics of Michelia chapensis seedlings.
    ZHOU Huan, WEI Ruping, LI Jiyue, SU Yan, HU Dehuo, ZHENG Huiquan
    2024, 43(3):  709-715.  doi:10.13292/j.1000-4890.202403.041
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    To elucidate the adaption mechanism for the growth and photosynthetic capacity of Michelia chapensis under different light intensities, two-year-old seedlings were treated with five shading levels of 100% (CK), 70% (T1), 50% (T2), 30% (T3) and 10% (T4) of natural light intensity for one year, after that the growth and photosynthetic characteristics were measured. The results showed that survival rate, plant height and ground diameter were significantly higher under the 70% and 100% light intensity treatments compared with other treatments. The highest value (8.553 μmol·m-2·s-1) of net photosynthetic rate (Pn) was recorded in the 70% light intensity treatment. With increasing shading intensity, Pn values decreased gradually. The decrease of Pn in the 50% natural light intensity treatment was mainly caused by stomatal limitation, but by non-stomatal limitation under the 30% and 10% natural light intensity treatments. Compared to other shading treatments, leaves under the 100% and 70% natural light intensity treatments had higher maximum net photosynthetic rate (8.166 and 8.735 μmol·m-2·s-1), light saturation point (1215.956 and 1145.328 μmol·m-2·s-1), and light compensation point (16.28 and 13.572 μmol·m-2·s-1). In particular, with increasing shading intensity, the actual photochemical quantum yield of PSII (ΦPSII), photochemical quenching coefficient (qp) and proportion of photochemical reaction energy (P) increased gradually, while non-photochemical quenching coefficient (NPQ) decreased gradually. All the treatments did not affect maximum photochemical quantum yield (Fv/Fm) and potential activity (Fv/F0). The results indicated that M. chapensis seedlings could reduce light compensation point, light saturation point, net photosynthetic rate and dark respiration rate, while increase the openness of PSII reaction center, electron transfer activity and light use efficiency, thus enhancing growth ability under moderate and serious shading conditions. Our results suggested that 70% of natural light intensity was the most optimal for the growth of M. chapensis seedlings.

    Effects of salt stress on chloroplast ultrastructure and photosynthetic fluorescence characteristics of Lumnitzera littorea (Jack) Voigt seedlings.
    CHEN Wei, TONG Yuyan, FENG Yu, HAO Lulu, ZHANG Huiyu, YUE Danfei, ZHANG Ying, ZHENG Chunfang
    2024, 43(3):  716-723.  doi:10.13292/j.1000-4890.202403.029
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    Exploring the response mechanisms of Lumnitzera littorea seedlings to salt stress can provide theoretical basis of protecting this endangered species. Here, we examined the effects of different concentrations of NaCl (50, 150, 450, 750 mmol·L-1) on plant growth, leaf photosynthesis, fluorescence parameters, changes of photosynthetic pigments, antioxidant enzyme activities, chloroplast ultrastructure, and stomatal characteristics. The results showed that under 150 mmol·L-1 NaCl treatment, net photosynthetic rate (Pn), stomatal conductance (Gs), potential maximum light energy conversion efficiency (Fv/Fm) and actual light energy conversion efficiency (ΦPSII), contents of total chlorophyll (Chl) and carotenoid (Car), activities of superoxide dismutase (SOD) and peroxidase (POD) were significantly higher than those of other treatments. When the NaCl concentration exceeded 450 mmol·L-1, values of the above indices decreased significantly, while the intercellular CO2 concentration (Ci), contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2), the production rate of superoxide anion (O2-·) significantly increased. Leaf malondialdehyde (MDA) content under 750 mmol·L-1 NaCl exhibited 56.58% higher than that of 150 mmol·L-1 NaCl. In addition, under 750 mmol·L-1 NaCl stress, the boundary of chloroplast membrane was gradually blurred, and the starch particles and osmiophilic particles increased and expanded. More importantly, the matrix and grana lamella were gradually loose and deformed. Furthermore, the stomatal opening of leaves was reduced or even closed. Our results indicated that 150 mmol·L-1 NaCl was the optimal concentration for the growth and development of L. littorea seedlings. When NaCl concentration exceeded 450 mmol·L-1, photosynthetic capacity was reduced by inducing unbalance of antioxidant system, inhibiting the photosynthetic pigment synthesis, and preceding stomatal closure and damaging the chloroplast, which eventually led to plant wilting.

    Effects of water-saving irrigation, reduced nitrogen application and different cultivars on CH4 emissions in a double rice cropping system
    SONG Chunyan, LI Yu’e, WAN Yunfan, QIN Xiaobo, ZHANG Xinyu, ZHU Bo, HU Yanyan, WANG Bin
    2024, 43(3):  724-732.  doi:10.13292/j.1000-4890.202403.028
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    Straw return, high-efficiency fertilizer, water-saving irrigation, and reducing nitrogen application are the main technologies for agricultural green development in China. High-yield but low-emission cultivar is an important direction for reducing CH4 emission in paddy fields. In this study, a field experiment was conducted to investigate the effects of straw return combined with nitrogen reduction application and water-saving irrigation on CH4 emission of different double-cropping rice cultivars, using static chamber-gas chromatography. A split-plot experimental design was adopted, with four main plot factors: urea + intermittent irrigation (U), reduction of urea 20% + straw return + intermittent irrigation (US+S), reduction of controlled release urea 20% + straw return + intermittent irrigation (CRUS+S), reduction of urea 20% + straw return + water-saving irrigation (US+S+SWD), crossed with two sub-plot factors: conventional rice and hybrid rice. The results showed carbon input, nitrogen input, irrigation amount, and tillering number were main factors affecting CH4 emission of double cropping rice field. Nutrients from straw return could replenish 20% reduction of nitrogen fertilizer, and significantly promoted CH4 emission for both cultivars, among which the emissions of conventional rice increased by 60.0%-107.8%, and the emissions of hybrid rice increased by 99.8%-107.8%. This was mainly attributed to the large amount of organic carbon input by straw. Compared with US+S, straw return with controlled-release urea increased CH4 emissions by 1.8%-9.7%, except for conventional late rice. Water-saving irrigation significantly reduced CH4 emissions by 15.9%-23.1% with straw return. There were no significant differences in yield among treatments, indicating that straw return combined with nitrogen fertilizer reduction and water-saving irrigation could achieve stable yield. CH4 emission and yield of hybrid rice were slightly higher than those of conventional rice, but without significant differences. In general, straw return significantly increased CH4 emission, controlled-release urea and reduced nitrogen application did not affect CH4 reduction, while water-saving irrigation could effectively reduce yield-scaled CH4 emission under straw returning. Therefore, with the increases of straw return rates in paddy fields, optimizing water management to promote straw aerobic decomposition is the key to control CH4 emission.

    Hyperspectral estimation of SPAD in different leaf positions of waterlogged winter wheat.
    GAO Xiaomei, LI Yanli, XIONG Qinxue, XU Le, LI Jifu, LI Xinzhu, WANG Xiaojun
    2024, 43(3):  733-740.  doi:10.13292/j.1000-4890.202403.003
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    Real-time and accurate acquisition of chlorophyll content information is of great significance for timely understanding crop damage degree, guiding agricultural production, and estimating yield. To explore the optimal estimation model for the soil and plant analyzer development (SPAD) in different leaf positions of waterlogged winter wheat, a plot experiment with a waterlogging stress gradient in winter wheat field under controlled drainage and irrigation was established. The correlation between 15 commonly used hyperspectral indices and SPAD was analyzed. The SPAD estimation results of waterlogged winter wheat leaves were compared using hyperspectral indices combined with the multiple linear regression, support vector machine, BP neural network, decision tree, and random forest models. The results showed that compared with normal winter wheat, there was no significant difference for SPAD and the value of hyperspectral reflectance under short-term waterlogging (less than 3 d). The SPAD was significantly decreased after more than 9 d waterlogging, and the value was close to 0 in the later growth period. The 15 hyperspectral indices were all correlated with the SPAD (P<0.05), with the correlations between SPAD and the four indices (Ctr2, Dy, NDVI and SIPI) being the highest with the absolute correlation coefficient of 0.880, 0.868, 0.868 and 0.833, respectively. Compared with the SPAD estimation of the L1, L2, and L3 leaves, the results of average SPAD were the best, with the R2 of 0.719. The SPAD estimation models constructed with random forest model was the best for different leaf positions, with R2, RMSE and RE of 0.824, 4.359 and 2.96%, respectively. Therefore, the average SPAD value could be used to estimate the SPAD of waterlogged winter wheat based on hyperspectral technology, and the random forest estimation model was best.

    Effects of planting patterns and irrigation quotas on light interception at different canopy layers and yield formation of machine-picked sea-island cotton
    WANG Xin, LIN Tao, CUI Jianping, ZHANG Pengzhong, TANG Qiuxiang, GUO Rensong, WANG Liang, SHAO Yajie
    2024, 43(3):  741-748.  doi:10.13292/j.1000-4890.202403.004
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    Optimizing the spatial distribution of light interception is a key strategy for creating a reasonable individual and group canopy structure in cotton fields, which could increase yield and machine-picking efficiency and realize the integration of agricultural machinery and agronomy. We examined the effects of planting patterns and irrigation quotas on light interception at different canopy layers and yield formation of machine-picked sea-island cotton. A field experiment was carried out following a split-plot design in Xinjiang, Northwest China. Three planting patterns included: one film with three equal-width rows (S3), one film with four wide/narrow rows (S4), and one film with six wide/narrow rows (S6) with the same planting density. Three irrigation quotas included: 3150 m3·hm-2 (W1, moderate deficit, 50% field capacity), 4050 m3·hm-2 (W2, mild deficit, 75% field capacity), and 4980 m3·hm-2 (W3, full irrigation, 100% field capacity). The results showed that increased row spacing and mild deficit watering could reduce the rate of decline of leaf area index and increase the PAR transmittance (Tr) of the lower canopy. The Tr of top, middle, and bottom layers of the canopy was distributed uniformly under S3W2 treatment, roughly in the 2∶2∶1 ratio. The distribution ratio of reproductive organs, the quality of cotton bolls, and the yield were greatly improved as a result of higher intercepted PAR rate (In) of the lower layer, despite a declining trend in the total In of the canopy. Water consumption efficiency was significantly decreased by increasing irrigation quota and row spacing. Our results suggests that the treatment of one film with three rows (S3) and mild deficit irrigation quota (4050 m3·hm-2) did not decrease cotton yield and water use efficiency, instead of the relative balance of them, due to advantages for increasing PAR light energy transfer in the middle and lower portion of the canopy and promoting. Our results are of great significance for promoting the integration of agricultural machinery and agricultural technology of sea-island cotton and for realizing the collaborative improvement of yield and machine-picking- quality.

    Relationship between leaf-litter nutrient stoichiometry and resorption of Zanthoxylum planispinum var. dintanensis at different altitudes.
    DENG Xuehua, YU Yanghua, XIONG Kangning, ZHANG Shihao, KONG Lingwei
    2024, 43(3):  749-757.  doi:10.13292/j.1000-4890.202403.012
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    Clarifying the stoichiometric characteristics of leaves and litters and nutrient resorption efficiency is helpful to understanding the mechanisms of nutrient conservation and utilization of Zanthoxylum planispinum var. dintanensis at different altitudes in the Guizhou karst plateau canyon area. Leaves and litters of Zanthoxylum planispinum var. dintanensis at different altitudes (531, 640, 780, 871, and 1097 m) were collected. The differences of nutrient concentration, stoichiometry and nutrient resorption efficiency with increasing altitude were analyzed, and the relationship between nutrient resorption and stoichiometry was elucidated. The results showed that the concentrations of organic carbon (OC), total phosphorus (TP), and total iron (TFe) in leaves and litters were highest at the altitude of 780 m. The total manganese (TMn) and total magnesium (TMg) concentrations in leaves, and TMg concentration in litters showed an increasing trend with altitude. Total nitrogen (TN), total potassium (TK) and total calcium (TCa) concentrations in both leaves and litters did not vary with altitude. With increasing altitude, leaf and litter C∶P, Fe∶Mn, and C∶Ca showed a trend of increasing first and then decreasing, while Ca∶Mg showed a decline trend. Nutrient resorption efficiency in leaves was not completely consistent with altitude variation. The P and K resorption efficiencies at the altitude of 780 m were the highest, while the N, Fe, and Mn resorption efficiencies were highest at 871 m. The Ca and Mg resorption efficiencies at 1097 m were significantly higher than those at other altitudes. The resorption efficiencies of P, N, and Fe at 1097 m were all negative. The results of redundancy analysis showed strong correlations between leaf nutrient resorption efficiency and stoichiometry.

    Distribution characteristics of tetracycline resistance genes in black soil farmland and vegetables.
    WU Yi, ZHANG Xun, WANG Baoyu, GAO Chengcheng, LI Xinyue, AN Jing
    2024, 43(3):  758-765.  doi:10.13292/j.1000-4890.202403.033
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    Antibiotics and the resistance genes can enter farmland soil through fertilization of animal manure, bringing potential ecological risks to the soil-vegetable system. We examined the distribution characteristics of antibiotic resistance genes in the soil-vegetable system, with tetracycline resistance genes (TRGs) as a research object. The distribution characteristics of typical TRGs were analyzed in three kinds of raw vegetables (pakchoi, lettuce, cherry radish). The effects of vegetable root system disturbance on the diversity and abundance of TRGs in the rhizosphere soil were explored, and the correlation of TRGs between vegetable and soils were analyzed. The results showed that TRGs and mobile genetic elements (MGEs) were detected in vegetables and rhizosphere soil, with detection types and abundance following an order of rhizosphere soil>root>leaf. The types and abundances of TRGs and MGEs were higher in roots than in leaves of three tested vegetables. The detection rate and abundance of tetD-01, tetG-01, tet-T, tet(32), IS613, tnpA-04, intI-1(clinic) were prominent. TRGs and MGEs were higher in rhizosphere soil of cherry radish than that of lettuce and pakchoi. The distribution of some TRGs in soil and vegetable systems was significantly positively correlated with MGEs. Our results can provide data support for reveling the safety risks of TRGs in the soil-vegetable system.

    Effects of photovoltaic panels on plant community characteristics and species diversity in meadow steppe.
    REN Naipeng, LI Yikun, ZHU Boquan, WANG Yifan, LIANG Wenchao, LIU Xiangping
    2024, 43(3):  766-772.  doi:10.13292/j.1000-4890.202403.045
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    To explore the plant community characteristics and species diversity of meadow steppe of the national photovoltaic and energy storage empirical experimental platform in Datong District, Daqing City, Heilongjiang Province, and to examine the influence of different habitats of photovoltaic electric field (between photovoltaic panels and under photovoltaic panels) on plant communities, we conducted a quadrat survey to investigate plant community characteristics. The differences of species composition and importance values, quantitative characteristics of community and species diversity were compared under and between photovoltaic panels. The results showed that species with the highest importance value in the photovoltaic field was Leymus chinensis, followed by Puccinellia tenuiflora. The plant community quantitative characteristic values of L. chinensis, P. tenuiflora, Phragmites australis, Suaeda salsa, and Eleocharis intersita in the habitat between photovoltaic panels were higher than those of under photovoltaic panels, and that of Potentilla anserina under photovoltaic panels was higher than that between photovoltaic panels. Shannon index, Margalef index and Simpson index of the community between photovoltaic panels were higher than those under photovoltaic panels. There was a significant positive correlation (P<0.05) among Shannon index, Margalef index, and Simpson index. Pielou index was non-significantly negatively correlated with the other three indices. The correlation coefficient between Simpson index and Margalef index was the highest. The values of most plant community quantitative characteristic were higher in the habitats between the photovoltaic panels than that under the photovoltaic panels, with higher species richness and more stable community structure in the habitats between the photovoltaic panels.

    Morphological plasticity induced by plant-plant interactions in karst-adaptive species under different nutrient conditions.
    CHEN Linli, WANG Shu, CHEN Jiaxing, YIN Renya, HOU Xiali, YANG Qingzhu
    2024, 43(3):  773-782.  doi:10.13292/j.1000-4890.202403.022
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    Investigating how nutrient conditions influence morphological plasticity induced by plant-plant interactions can help reveal the adaptation strategies of karst-adaptive plant species in coping with variations of environmental factors. In this study, we explored the effects of nutrient availability on the plasticity in biomass and morphological traits induced by intraspecific or interspecific interactions by treating Bidens pilosa and Buddleja davidii with and without intraspecific and interspecific interactions under two conditions of nutrient addition and no addition (control). In the no-nutrient condition, the total biomass of B. pilosa and B. davidii under the intraspecific interaction decreased by 9.2% and 14.4%, respectively, which mainly resulted in competition effect, with little interspecific competition. When nutrients were added, intraspecific facilitative effect became dominant, increasing by 35.1% and 41.3% respectively. B. davidii showed interspecific facilitative effect, increasing by 34.6%, but not in B. pilosa. Compared to control, intraspecific interaction decreased root biomass of B. davidii and leaf biomass of B. pilosa in low nutrient conditions. When nutrients were added, it increased stem biomass of B. davidii and decreased specific leaf area of B. pilosa. By contrast, interspecific interaction increased root∶shoot ratio of B. davidii, decreased root biomass, and increased stem biomass for B. pilosa under low nutrient conditions. When nutrients were added, it increased root∶shoot ratio and root biomass for B. davidii, and increased ground diameter of B. pilosa. These results suggested that abiotic factors can affect the plastic response of plants through mediating the strength of intraspecific and interspecific interactions. The distinct contrast between trait plasticity induced by intraspecific and interspecific interactions reflected striking differences in growth and adaptation strategies between the two species, with belowground growth and aboveground growth being dominant for B. davidii and B. pilosa, respectively. Intraspecific interactions can lead to more intense belowground and aboveground competition for the two species, respectively. Under interspecific interactions, however, they may be able to avoid growth advantages, complementing each other in resource utilization, thus competition weakened and the facilitation pronounced. Such a strategy would be beneficial for the better coexistence of karst-adaptive plant species in coping with the abiotic challenges.

    Bird diversity and its affecting factors on the riverbanks of main rivers entering Chao Lake.
    YANG Yating, ZHANG Zhongfang, XIA Shanshan, ZHOU Lizhi
    2024, 43(3):  783-794.  doi:10.13292/j.1000-4890.202403.021
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    Riverbanks are important components of riverine ecosystems and provide important habitats for wildlife. Birds are common animals on riverbanks, the community composition of which is influenced by local habitat factors. From August 2021 to July 2022, a total of 45 line transects were established on three types of riverbanks of five rivers entering Chao Lake. We investigated the distribution and populations of bird species on the riverbanks in terms of the distance from the road, bank width, slope gradient, and the cover and average height of trees, shrubs, and herbs. Furthermore, we examined the effects of different riverbank structures on bird diversity. The relationship between bird diversity and habitat factors was quantified using multiple stepwise regression analysis. The results showed that 116 species of birds (14 orders and 44 families) were recorded across the three types of banks, including 36 species of waterbirds, 11 species of national-level protected birds, 35 species locally protected by Anhui Province, and one critically endangered (CR) species in the IUCN Red List of Threatened Species. Compared with other types of bank habitats, the artificial bank had the greatest impact on bird diversity, and the natural bank was more conducive to maintaining bird diversity. Herbaceous plant cover and its average height, bank slope gradient, and bank width significantly affected bird diversity. The highest bird species richness was observed on the bank with natural wide slopes, indicating that birds favored gentle natural bank habitats. Our results can provide a scientific basis and technical support for the construction, management, and biodiversity conservation of the riverbanks around Chao Lake.

    Characteristics of fish community structure in the sea area of Dachen Island.
    ZOU Qindong, WANG Zhenhua, ZHANG Shouyu, CHENG Xiaopeng, CHEN Yihui, ZHOU Yi
    2024, 43(3):  795-803.  doi:10.13292/j.1000-4890.202403.005
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    We analyzed the spatial and temporal variations of fish community structure at the local scale in the waters around Dachen Island, using data of bottom trawl surveys collected from 21 sites in September and November 2020, as well as January and April 2021. A total of 99 fish species were recorded, belonging to 15 orders, 48 families, and 81 genera. 50.51% of those fishes belonged to the order Perciformes. Harpadon nehereus was the most dominant species throughout the year. Amblychaeturichthys hexanema dominated during all seasons except summer. Pampus echinogaster was dominant in summer and autumn. Migratory species such as Muraenesox cinereus, Pennahia macrocephalus, Larimichthys polyactis and Larimichthys crocea dominated in only one season. The results of cluster analysis and nonparametric multidimensional scaling showed two types of fish communities around Dachen Island during summer, autumn, and winter, which were near-estuarine fish communities and open sea fish communities. In spring, fish communities could be grouped into reef island communities and off-island communities, with significant differences in species composition among different groups in each season (P<0.05). Results of redundancy analysis showed that water depth, surface temperature, bottom salinity and bottom temperature were the primary factors affecting fish community structure in this area (P<0.05). Our results indicated significant regional and seasonal variations in the fish communities in the sea area around Dachen Island, and that fish communities were dominated by small-sized and low economic value fish.

    Soundscape composition and acoustic activity assessment of Nomascus hainanus habitat.
    GUO Anqi, LIU Yukun, YU Xinwen, ZHANG Xu, CHEN Yan, LUO Li, GAO Jiajun, YANG Caiyun
    2024, 43(3):  804-814.  doi:10.13292/j.1000-4890.202403.023
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    Hainan Bawangling Nature Reserve, the only national nature reserve in China that protects Nomascus hainanus and their living environment, has rich acoustic soundscape resources consisted of sounds from N. hainanus, birds and other animals. Exploring the soundscape composition and acoustic activities of N. hainanus habitat would shed light on the daily behavior of N. hainanus and provide technical support for ecological conservation. Using passive acoustic monitoring techniques, huge amount of sound data were collected in the protected area. The soundscape and its daily variations were characterized by analyzing the distribution of the soundscape power in different frequency ranges. Four widely used acoustic indices, including ACI (acoustic complex index), ADI (acoustic diversity index), BI (bioacoustic index), and NDSI (normalized difference soundscape index), were extracted to evaluate N. hainanus sounds. The Random Forest method was employed to classify sounds with the four acoustic indices as predictor variables and the presence or absence of N. hainanus sounds as response variables. The results showed that: (1) The soundscape power in different frequency ranges reflected different acoustic community information, with significant temporal variations, indicating the dawn chorus and dusk chorus activities of birds, N. hainanus and other animals. Among them, 1-2 kHz was consistent with the N. hainanus dawn chorus, and 2-5 kHz was in line with the circadian rhythm of birds and other animals. (2) The changing trends of acoustic indices with and without N. hainanus calls were significantly different, with the largest difference of NDSI and the least of ADI. (3) Four acoustic indices gave better classification results for the sound data of N. hainanus, with a crossvalidated AUC value of 0.9764. This study effectively reveals the activity characteristics of animals in the experimental area based on soundscape, indicating the feasibility of using acoustic index to evaluate the call of N. hainanus, and thus lays the foundation for acoustic monitoring of Hainan Bawangling area and N. hainanus.

    Optimization of the culturing medium for Penicillium raistrickii F-1 and determination of its virulence against Bactericera gobica.
    LI Qiuyu, CHAI Junfa, PU Yanli, MA Wentian, ZHANG Xiaoli, WANG Fang, JIA Yanxia
    2024, 43(3):  815-822.  doi:10.13292/j.1000-4890.202403.047
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    Penicillium raistrickii is a strain with biological control effect, which was isolated from the body of the infected Bactericera gobica by our research group. Enhancing the growth performance of P. raistrickii has a great significance to improve its control effect. In this study, a single-factor experiment was conducted to select and optimize different medium components and their concentrations for culturing P. raistrickii using spore production as an indicator. We determined the virulence of P. raistrickii culturing broth against the third instar of B. gobica. The results showed that the optimized medium was composed of 40 g·L-1 soluble starch, 1 g·L-1 yeast powder, 1 g·L-1 K2HPO4, 1.5 g·L-1 MgSO4·7H2O, 0.5 g·L-1 KCl and 0.01 g·L-1 FeSO4, which increased spore production by 9.84 times compared to the basic medium. The results of the toxicity assay showed that the corrected mortality rate of the third instar of B. gobica treated by the P. raistrickii culturing broth with the optimized medium at 7 d increased by 25.56% compared to the basal medium. Based on the spore production and virulence results, the optimized medium is more effective than the basic medium in culturing P. raistrickii and controlling B. gobica, which provides a foundation for improving the biological control effect of P. raistrickii against B. gobica.

    Spatial-temporal variations and influencing factors of vegetation net primary productivity in Xiamen-Zhang-zhou-Quanzhou Region from 2001 to 2020.
    WANG Shenghong, LU Dongfang, CHEN Yuru, TANG Yalan, ZHENG Yushan, HUANG Yubin
    2024, 43(3):  823-832.  doi:10.13292/j.1000-4890.202403.002
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    Net primary productivity (NPP) is a crucial index for evaluating the regional carbon cycle. Understanding the spatiotemporal variation of NPP and its influencing factors has practical significance for formulating scientific and rational sustainable development strategies. In this study, the spatiotemporal variations of NPP in the Xiamen-Zhangzhou-Quanzhou Region during 2001-2020 were examined using correlation analysis, land cover transfer matrix, and contribution analysis in combination with spatial analysis methods based on land cover data, climate data (temperature and precipitation), and NPP products of MODIS platform. The effects of land cover change and climate change on NPP were quantitatively described, and the driving factors of NPP change were analyzed. The results showed that the annual mean NPP in the Xiamen-Zhangzhou-Quanzhou Region fluctuated in the range of 938.1-1100.9 g C·m-2·a-1, without obvious decreasing trend in general. Forest land had the highest total NPP value (11117.40 Gg C) and growth rate (103.75 Gg C·a-1) among all land cover types. The NPP in Xiamen-Zhangzhou-Quanzhou Region was positively correlated with air temperature and negatively correlated with precipitation. The partial correlation between NPP and air temperature was stronger than that between NPP and precipitation. The NPP in most areas of this region was affected by non-climatic factors. In different periods, the dominant factors of NPP change in different land cover types shifted between climate change and land cover change.

    Suitable distribution pattern and early warning of invasive species Mirabilis japala under climate change scenarios in China.
    SU Qitao, ZOU Zhengrong, DU Zhixuan, ZHOU Bing
    2024, 43(3):  833-841.  doi:10.13292/j.1000-4890.202403.046
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    It is of great theoretical and practical significance to clarify the distribution patterns of invasive plants under global climate change for the control and prevention of invasive plants. Based on 228 distribution points nationwide and 13 major environmental and climatic factors (from 19 environmental and climatic data of WorldClim), we simulated and analyzed the major environmental factors affecting the distribution of invasive species Mirabilis japala using MaxEnt model. Combined with ArcMap software, we analyzed the distribution pattern and change pattern of the suitable area of M. japala under three climate scenarios (RCP2.6, RCP4.5, RCP8.5) in the current and future (2050s and 2070s). The results showed that the prediction accuracy of MaxEnt model was extremely high, with the AUC value of training data and test data being 0.983 and 0.980, respectively. Precipitation of the warmest quarter was the main environmental factor affecting the distribution of M. japala. In current climate condition, the total suitable area was 429.06×104 km2, accounting for 44.52% of the total land area, located in all provinces except Xinjiang in China. Under the three climate scenarios in the future, the potential distribution area of M. japala will be shrinking in the south, expanding in the north, and the total area of suitable area will increase. The southern part of Jilin, the southern part of Heilongjiang and the southeastern part of Inner Mongolia are the main expansion areas, and the center of mass migrates to the high latitude areas in the northeast direction. In conclusion, under the scenario of global climate change, the suitable area of M. japala in China will increase and expand  northward. Some regions in Heilongjiang, Inner Mongolia, southern Jilin, southern Tibet, northern Sichuan and southern Gansu should take precautions to prevent the expansion of M. japala.

    Spatial and temporal variations of habitat quality in Dianchi Lake basin based on land use/cover change.
    YANG Han, LI Xiaona, DENG Zhongjian, ZHANG Zhuoya, PAN Huiping
    2024, 43(3):  842-850.  doi:10.13292/j.1000-4890.202403.038
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    Dianchi Lake is the largest high-altitude freshwater lake in southwest China and the largest freshwater lake in Yunnan Province. Understanding the spatiotemporal variations of land use/cover types and habitat quality in the Dianchi Lake basin is of great significance for the protection of the ecological environment in the basin. Based on land use/cover data from 1988 to 2018, we analyzed the spatiotemporal variations in habitat in the Dianchi Lake basin using InVEST model and the spatial analysis tool of GIS, and quantified the spatial aggregation and evolution characteristics of habitat quality using Moran’s I index and hot spot analysis. The results showed that: (1) Land use/cover types in the Dianchi Lake basin changed dramatically, from the dominance of farmland in 1988 to the dominance of urban land in 2018. (2) The overall habitat quality in the basin declined, with lower habitat quality in the urban areas surrounding Dianchi Lake and higher quality in the surrounding mountains and hills, but distributed sparsely. (3) The cold and hot spots of habitat followed aggregated distribution. Hot spots were mainly located in the surrounding forests, and their range gradually shrunk with time. The cold spots were located in the urban areas surrounding Dianchi Lake, and their number increased greatly over time. Our results indicate that the drastic change of land use/cover during urbanization is a main reason for the changes of urban habitat, providing reference for optimizing land use types and improving or maintaining biodiversity in Dianchi Lake Basin.

    Measurement and prediction of eco-environmental quality on the Loess Plateau based on coupled coordination degree model.
    YANG Tao, DANG Guofeng
    2024, 43(3):  851-860.  doi:10.13292/j.1000-4890.202403.007
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    As a basis of ecological civilization construction, the assessment of eco-environmental quality is of great significance for adapting to climate change and reasonably developing and protecting eco-environment. Based on vegetation coverage, terrain index and population distribution, and ecological elasticity limit derived from MODIS and land use dataset from 2000 to 2020, we assessed the evolution of environmental carrying capacity of the Loess Plateau with highly fragile eco-environment. The coupling coordination degree model was used to comprehensively characterize the regional eco-environment. A standard deviation ellipse method was used to investigate the change of center of gravity and the transfer path of coordination degree. Elman Neural Network with particle swarm optimization was used to predict the future trend of ecological environment. The results showed that since 2000, the environmental carrying capacity of the Loess Plateau exhibited a spatial pattern with higher in the southeast and lower in the northwest, and the index increased slowly with a rate of 0.0625 per year. The ecological elasticity limit was consistent with land use pattern, and the index exponentially ascended with a low level. The coupled coordinate coefficient changed from slight discordance to primary coordination. The core of coupled coordination degree shifted to southeast and exhibited a spatial pattern with centripetal aggregation in the northeast-southwest direction and diffusion in northwest-southeast direction. It is predicted that the system coupling coordination degree of environmental carrying capacity and ecological elasticity limit will increase steadily in 2030, which indicates that the eco-environmental quality of the Loess Plateau will gradually become coordinated in the future, but with significant difference in the growth rate of different regions.

    Variations of runoff and sediment and its attribution analysis in Zhangshui watershed of the upper reaches of Ganjiang River.
    ZHANG Ting, LIU Shiyu, SHENG Fei, LI Jun, YU Minqi
    2024, 43(3):  861-868.  doi:10.13292/j.1000-4890.202403.006
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    The runoff and sediment situation in the watershed has changed with climate change and the intensification of human activities. Quantitative analysis of the runoff and sediment effects of precipitation variation and human activities is a hot topic in current water science research. Based on the hydrological and meteorological observation data of Zhangshui watershed in the upper reaches of Ganjiang River from 1961 to 2020, we quantitatively analyzed the contribution rate of precipitation variation and human activities to the changes of runoff and sediment, and the critical value of the runoff and sediment effect of human activities to the annual precipitation response by using the slope change ratio of accumulative quantity and empirical statistical analysis. The results showed that precipitation and runoff showed a nonsignificant downward trend (P>0.05), and the sediment transport showed a significant downward trend (P<0.001). The abrupt change of precipitation and runoff was in 2003, and the abrupt change of sediment was in 1998. The contribution rates of precipitation variation and human activities to runoff reduction were 10.7% and 89.3%, and to sediment reduction were 3.5% and 96.5%, respectively. The critical values of runoff and sediment reduction effects of human activities in response to annual precipitation were 1170 mm and 858 mm, respectively. Our results could provide scientific basis for watershed ecological construction and optimal management of water and land resources.

    Mercury exposure and health risk assessment in typical lead-zinc mining areas and Guiyang City.
    WANG Dawei, KONG Lin, XU Xiaohang, HAN Jialiang, LIU Jiemin, QIU Guangle
    2024, 43(3):  869-877.  doi:10.13292/j.1000-4890.202403.032
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    To assess food contamination levels of organic (MeHg) and inorganic mercury associated with mining and urban environments in Guizhou, we analyzed 503 samples from Hezhang County (lead-zinc mining area) and Guiyang. The health risk associated with dietary consumption was assessed using Monte Carlo simulations. The highest levels of total mercury were 39 and 18 ng·g-1 in the samples from the mining area and the urban residential area, respectively. The corresponding highest measurement values for MeHg were 1.7 and 7.7 ng·g-1, respectively. The investigated foodstuffs such as rice, potatoes, chicken eggs, fish, pork did not contain significant levels of mercury contamination, with the exception of certain vegetables that frequently showed levels above the current limit standard of 10 ng·g-1. 14.7% (lead/zinc mining area) and 17.7% (residential area) of vegetable samples exceeded the limit specified in China’s National Food Safety Standard (GB 2672-2017). Dietary inorganic mercury exposure was similar for food with different origins (residential area: 0.031 μg·kg-1·d-1, lead-zinc mining area: 0.032 μg·kg-1·d-1), while exposure to organic mercury was nearly twice greater in the urban environment (6.0 vs. 3.2 ng·kg-1·d-1). In general, the average daily exposure to inorganic mercury and MeHg was lower than the provisional weekly tolerable intake (PTWI) of 4 μg·kg-1·week-1 for IHg by WHO/JECFA and the reference dose (RfD) of 0.1 μg·kg-1·d-1 for MeHg established by USEPA, respectively. Hazard index in both regions was much less than unity, suggesting no obvious non-carcinogenic health risks.

    Effects of availability and form of exogenous nitrogen on plant growth and physiology: Progress and prospects.
    ZHANG Qinze, HAO Guang, LI Hongyuan
    2024, 43(3):  878-887.  doi:10.13292/j.1000-4890.202403.030
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    Nitrogen (N) is one of the most important nutrient elements controlling plant structure and function and maintaining ecosystem stability. The differences in exogenous N availability and form have significant effect on plant growth and physiological traits. Due to global climate change and intensified human activities, the mobility and deposition of N into terrestrial ecosystems increase rapidly and the form of N deposition is also changing, which seriously damages the normal growth of plants and the balance and stability of ecosystem, and has become a hot topic. We summarized the effects of different N addition levels and forms on plant growth, photosynthesis, nutrient absorption, and metabolic enzyme activity. We concluded that: (1) proper N input could promote plant growth, photosynthesis, and nutrient absorption capacity, but has inhibiting effect on plants once exceeding the threshold of plant tolerance; (2) due to the difference in plant preference for N form absorption, the effects of ammonium or nitrate N on plant growth, photosynthesis, nutrient absorption, and metabolic enzyme activity are different, and the appropriate ratio of ammonium and nitrate N has a more significant promotion effect on most plants than the addition of a single N form. Four important research directions should be considered in future: (1) carrying out large scale longterm positioning observation of manipulative experiments; (2) exploring the microscopic mechanism of N form affecting plants using molecular biology techniques; (3) focusing on the effect of soil rhizosphere environment on root N uptake; (4) comprehensively analyzing the interaction between N addition and other environmental factors and accurately assessing typical plant population dynamics and community structure changes. Our study provides theoretical reference for exploring the mechanism of plant growth and physiology and enabling sustainability of plant production systems under exogenous N addition.

    Research progress on the effects of climate change on plant phenology of natural grasslands.
    SUN Jianping, LYU Wangwang, LI Bowen, LIU Shizhang, WU Jing, WANG Shiping
    2024, 43(3):  888-894.  doi:10.13292/j.1000-4890.202403.048
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    Plant phenology has always been a hotspot and frontier research in plant evolutionary biology, plant ecology, and climate change ecology, as it is closely associated with plant adaption and evolution, interspecies relationship, and ecosystem structure and functions, and it is greatly sensitive to climate change. Here, we review the main progresses and problems about the responses of the staring date and duration of phenological sequences to climate change based on three levels (i.e., individual, population, and community) with seven phenological sequences (i.e., onset of green-up, first budding-set, first flowering, first fruiting-set, nutrition after fruiting-set, first coloring, and complete coloring). We further proposed some scientific questions and prospects to promote the development of plant phenological studies in China.

    Factors affecting soil organic carbon density of Pinus tabuliformis aerial seeding plantation.
    ZHANG Junyu, WU Puxia, BU Yuankun, SU Shaofeng, LI Weizhong
    2024, 43(3):  895-903.  doi:10.13292/j.1000-4890.202403.043
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    Soil carbon pool is an important component of forest ecosystem carbon pool, which plays an important role in regulating carbon cycling of terrestrial ecosystems and atmospheric CO2 concentration. Previous studies mainly investigated the relationships between forest soil carbon and various factors (such as topography, vegetation, soil physical and chemical properties). However, key factors in the multiple factors and their interaction mechanisms are still unclear. Based on the observed data of 50 plots of Pinus tabuliformis aerial seeding plantation in Danfeng County, Shangluo City, Shaanxi Province, we used structural equation model to explore the influencing factors of soil organic carbon density. A total of 23 indices including stand structure, species diversity, biomass and soil physicochemical properties were selected as observation variables, and four latent variables including tree characteristics, shrub, herb and litter characteristics, other soil physicochemical properties, and soil organic carbon density were formed. A partial least square structural equation model was constructed. The results showed that: (1) 12 observation variables were included in the final structural equation model. Three observation variables were screened out from other soil physicochemical properties, namely, soil total nitrogen, soil total phosphorus, and soil water content. Five observation variables were selected from the latent variables of shrub, herb and litter characteristics, including shrub Simpson index, herb Simpson index, herb Margalef index, herb biomass, and litter layer thickness. Three observation variables were screened out from the latent variables of tree characteristics, including tree Simpson index, neighborhood comparison and number of tree species. (2) Other soil physicochemical properties were the direct influencing factors of the latent variable of soil organic carbon density (path coefficient of 0.877, P<0.01). Shrub, herb, and litter characteristics and tree characteristics were considered as the indirect influencing factors of the latent variable of soil organic carbon density (path coefficient of 0.552 and -0.299 respectively, both P<0.01). (3) The characteristics of shrub, herb, and litter affected the latent variable of soil organic carbon density by directly affecting other soil physicochemical properties (path coefficient of 0.630, P<0.01), and tree characteristics affected the latent variable of soil organic carbon density by directly affecting shrub, herb, and litter characteristics (path coefficient of -0.541, P<0.01). In conclusion, this study provides new insights into the relationship between different driving factors and has important implications for understanding soil organic carbon regulation in aerial seeding plantations.

    Refined meteorological risk analysis and zoning of Anji white tea.
    LI Shirui, ZHU Lanjuan, ZHAO Liang, BAI Jia, HU Bo, XU Jinping, SUN Rui
    2024, 43(3):  904-912.  doi:10.13292/j.1000-4890.202403.037
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    Meteorological disasters seriously threaten the high-quality development of tea industry. The refined assessment of meteorological disaster risks can provide scientific basis for the precise prevention and control of tea production disasters. Based on the natural disaster risk theory, the daily meteorological data of seven standard meteorological stations in Anji County and its surrounding areas from 1971 to 2020 as well as 23 automatic meteorological stations in Anji County from 2012 to 2020, statistical data of agricultural socioeconomy of 15 townships, and the multi-source information such as tea planting distribution map interpreted from GF-2 satellite remote sensing data and digital elevation model (DEM) data were adopted for calculation. We used the weighted comprehensive index method, fuzzy hierarchy analysis method, and Geographical Information System (GIS) technology to analyze the refined meteorological disaster risk and zoning for Anji white tea. The results showed that the maximum risk of the disaster factor and the maximum exposure of the disaster environment of Anji white tea were distributed in the high-altitude mountainous areas of the south, the highest value of the vulnerability of the disaster bearing body was distributed in the central plain, and the highest value of disaster prevention and mitigation ability was distributed in the central and eastern plain. Considering the comprehensive risk of each factor, the meteorological disaster risk of Anji white tea could be classified into three levels: low risk, medium risk, and high risk. The low-risk areas were mainly distributed in the north-central plain of Anji, accounting for 66.55% of the total area of Anji County. The medium-risk areas were mainly distributed in the middle and high altitude areas in the west and south of Anji County, accounting for 30.54% of the total area. The high-risk areas were mainly located in the high-altitude mountainous areas in the south, accounting for 3.01% of the total area. According to the tea planting map, 61.21%, 38.17%, and 0.62% of tea gardens in Anji County were distributed in low-risk, medium-risk, and high-risk areas, respectively. The refined risk zoning of meteorological disasters based on tea planting map could provide more accurate scientific basis for the management of Anji white tea.