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    10 April 2020, Volume 39 Issue 4
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    Effects of forest fire on carbon density of Eucalyptus robusta forest ecosystem in Guangdong Province.
    HU Hai-qing, LUO Si-sheng, LUO Bi-zhen, WEI Shu-jing, WANG Zhen-shi
    2020, 39(4):  1067-1074. 
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    As a non-continuous ecological factor, forest fire affects carbon pool and carbon distribution in forest ecosystems, and alters forest succession and carbon sequestration capacity. In this study, the burned sites ofEucalyptus robusta forests with different fire intensities were selected as the research object. A comparison method of adjacent plots was used in combination with field sampling and laboratory analysis, to investigate the effects of different forest fire intensities on the variation and spatial distribution patterns of carbon density of different ecosystem components in forest ecosystems. We found that forest fire reduced vegetation carbon density (P<0.05). Carbon density of vegetation in the plots with light, moderate and high fire intensities was 67.88, 35.68 and 15.50 t·hm-2, with a decrease of 15.86%, 55.78% and 80.79% compared to that of the control, respectively. After interference of light, moderate and high forest fire intensities, carbon density of litter was 1.43, 0.94 and 0.81 t·hm-2, respectively, with a reduction of 28.14%, 52.76% and 59.30%, respectively. Soil organic carbon density in forests with different forest fire intensities was lower than that of the control, and the reduction amplitude gradually became smaller with increasing soil depth. Soil organic carbon density of E. robusta forests was 103.30, 84.33 and 70.04 t·hm-2, respectively, which decreased by 11.67%, 27.89% and 40.11%, respectively. In forests with light, moderate and high forest fire intensities, ecosystem carbon density was 172.61, 120.95 and 86.35 t·hm-2, respectively, which decreased by 13.53%, 39.41% and 56.74%, respectively. In summary, forest fire disturbance reduced carbon density of E. robusta forests, which decreased with increasing forest fire intensity. Compared with the control, lightintensity forest fire interference had no significant effect on ecosystem carbon density (P>0.05), while moderateand highintensity forest fire interference had a significant effect on ecosystem carbon density (P<0.05).
    Restoration dynamics of near tonature forests in Shanghai.
    SONG Kun, GUO Xue-yan, WANG Ze-ying, HUANG Sha-sha, YAN Jia-yu, YE Jian-hua4, LE Ying5, YAN Ming5, WU Mei6, DA Liang-jun
    2020, 39(4):  1075-1081. 
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    Construction of near to nature forests is an important way to restore vegetation in cities. This method has been used in several Chinese cities, with new afforestation models beingemerged recently. To assess restoration dynamics of near to nature forests using different afforestation models, we carried out longterm monitoring on two near to nature forests in Shanghai, which were constructed by the Miyawaki model and a new deciduousevergreen bi cohortandsynusia model respectively. The restoration dynamics were compared between the two models in terms of species composition, vertical structure, life form component and population size of target species. The results showed that species composition became more similar with increasing recover years between the two forests. Over a decade, both models created a kind of mixed forests with deciduous trees dominating the canopy and evergreen trees dominating the understory. The new bi-cohort andsynusia model was better for the recovery of evergreen tree species, especially for the constructive species, Machilus thunbergiiand Cyclobalanopsis myrsinifolia. This study provides empirical evidence that near to nature restoration method could shorten restoration time from bare ground to later succession stage in subtropical region. We recommend restoring urban vegetation by the new bi-cohort and synusia model to construct near to nature forests.
    Carbon sequestration rate of Pinus sylvestris var.mongolica plantation and its responses to climate factors in Hulunbuir Sandy Land.
    CAO Gong-xiang, GUO Zhong, WANG Yun-ni, JI Meng, HAN Shan-shan, GENG Qing-chun, FENG Li-hong, LIU Hai-li
    2020, 39(4):  1082-1090. 
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    Pinus sylvestris var.mongolica is one of the main native plantation species in Hulunbuir Sandy Land. Understanding the response of biomass carbon density of Pinus sylvestrisvar.mongolicaplantation to changes of climatic factors is important for rational management to enhance carbon sequestration. We set three 30 m×30 m plots in plantation with stand age of 41 years in Hulunbuir Sandy Land. Using dendrochronological methods and empirical biomass equations, we estimated biomass, carbon density, and net vegetation carbon sequestration rate (CSR) of Pinus sylvestris var.mongolicaplantation in the past 41 years. Further, we analyzed the relationship between CSR and climatic factors, including monthly air temperature, humidity and precipitation. The results showed that carbon density increased with increasing stand age, with 2.58 t·hm-2 in 1977 to 87.97 t·hm-2 in 2017. The interannual variation of CSR showed a trend of increasing first and then decreasing. The average CSR was 2.13 t·hm-2·a-1, within a range of 1.37-3.21 t·hm-2·a-1. The CSR of Pinus sylvestrisvar. mongolicaplantation was positively correlated with precipitation in the growing season of previous year and current year, and negatively correlated with precipitation in the non-growing season. The CSR was negatively correlated with precipitation in last December and that in current March. The CSR was positively correlated with the average daily air relative humidity from August to September in previous year and current year. The CSR was negatively correlated with monthly average temperature, monthly average minimum temperature, and monthly average maximum temperature. In general, the CSR is affected by temperature and precipitation, with higher sensitivity to temperature. Our results highlight that CSR of Pinus sylvestrisvar.mongolica plantation could decrease in the future due to potential warming in Hulunbuir.
    Seed bank and seedling regeneration of Calamus tetradactylus in Ganzhaling, Hainan Province.
    2020, 39(4):  1091-1100. 
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    To reveal soil seed bank size and seedling regeneration capacity of Calamus tetradactylus in Ganzhaling of Hainan Province, we investigated seed distribution and natural regeneration seedlings of C. tetradactylus(≤40 cm) by setting up 30 grid plots (20 m × 20 m) and seven 1 m × 1 m quadrats in each plot along the diagonal. Random Forest method was used to analyze the effects of environmental factors on the abundance of seeds and seedlings. The results showed that seed distribution in soils was not uniform. Seeds in the soil seed bank were mainly concentrated in the litter layer. Class Ⅰ (0-9 cm) of C. tetradactylus seedlings was the main component of the regenerating seedlings, with a contribution of 61.63%. The conversion rate of class Ⅰ to class Ⅱ seedlings was low (39.18%), which was a key factor limiting C. tetradactylus seedling’s natural regeneration. Among all the examined environmental factors, canopy height, canopy density, litter thickness, and stand density were the main ones affecting seed distribution and seedling quantity. In summary, natural regeneration capacity of C. tetradactylus was low under natural conditions, and thus manual intervention and control measures should be adopted to promote the regeneration. To promote the successful natural regeneration ofC. tetradactylus, it is necessary to consider sitespecific environmental factors, such as pruning tree crown and thinning seedlings, which would improve the bedding environment of seeds and the conversion rate of C. tetradactylus seedlings.
    Effects of nitrogen addition on growth, photosynthetic characteristics and saponin content in two-year-old Panax notoginseng.
    CUN Zhu, ZHANG Jin-yan, CHEN Jun-wen
    2020, 39(4):  1101-1111. 
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    To provide a theoretical basis for rational fertilization, we explored the effects of different nitrogen (N) levels on growth, photosynthetic characteristics and saponin content of medicinal plants Panax notoginseng. Pot experiments were conducted to investigate leaf anatomy, root morphological characteristics, biomass, photosynthetic efficiency and saponin content in two-year-old P. notoginseng treated with different nitrogen levels (0 kg·hm-2, LN; moderate nitrogen, 225 kg·hm-2, MN; high nitrogen, 450 kg·hm-2, HN). The results showed that the thickness of upper epidermis, lower epidermis, palisade tissue and sponge tissue reached the highest value in the HN individuals. Total root length, main root length, root surface area, number of fibrous roots, root length, root length density, root mass ratio, root shoot ratio and specific leaf area reached the maximum value in the LN individuals. Root system activity was significantly higher in the MN individuals than in the other two treatments (P<0.05). With respect to the responses of photosynthesis to light and CO2 level, net photosynthetic assimilation, maximum photosynthetic assimilation at saturating light, carboxylation efficiency, maximum electron transfer rate and maximum carboxylation efficiency of MN individuals were significantly higher than those in the other two treatments (P<0.05). Nitrogen content per unit leaf area, chlorophyll content and the allocation of leaf N to photosynthetic tissues were highest in the HN treatment. Photosynthetic N use efficiency was the highest in the LN treatment, and total N content in roots was the highest in the MN treatment. Saponin content in roots of P. notoginseng was the lowest in the HN treatment. N surplus or N deficiency is unfavorable to growth and photosynthetic performance ofP. notoginseng. Decreased leaf thinness under LN or increased leaf thickness under HN treatment would inhibit CO2 diffusionin leaves. Under N deficiency, more saponinlike defensive compounds are needed for the survival of P. notoginseng. Under excessive N condition, saponin biosynthesis is weakened due to lower C/N ratio.
    Seasonal changes of soil organic acid concentrations in relation to available N and P at different stages of vegetation restoration in a karst ecosystem.
    PAN Fu-jing, ZHANG Wei, LIANG Yue-ming, WANG Ke-lin, JIN Zhen-jiang
    2020, 39(4):  1112-1120. 
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    Soil organic acids released by plants are important for improving soil nutrient availability. To clarify the relationships between soil organic acids and the concentrations and ratios of nutrients at different stages of vegetation restoration in a karst ecosystem, we measured the concentrations of oxalic acid, malic acid, acetic acid, organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrogen (AN) and phosphorus availability (AP), and microbial biomass carbon (MBC) in rhizosphere soils and bulk soils of six plant species (three for shrubland and three for primary forest) in dry and wet seasons. Our results showed that the oxalic acid concentrations of rhizosphere soils in primary forest were higher than those in shrubland in both seasons, whereas the concentrations of malic acid and acetic acid showed an opposite trend. Moreover, the concentrations of oxalic acid in rhizosphere soils in both vegetations were higher than those of bulk soils in both seasons. The concentrations of oxalic acid of rhizosphere and bulk soils were higher in the wet season than that in the dry season, whereas those of malic acid and acetic acid were lower. Furthermore, the oxalic acid concentrations were significantly positively correlated with SOC, TN, TP, AN, and N∶P ratios, and significantly negatively correlated with C∶N ratios. Soil AN and AP concentrations were significantly positively correlated with oxalic acid concentrations and MBC. Our results suggest that seasonal changes in organic acid exudate may be related to soil nutrient status and plant nutrition requirements, and that the interactions between organic acids and soil microorganisms may enhance nitrogen and phosphorus availability. Therefore, seasonal changes in organic acid concentrations of rhizosphere soils may be an important mechanism for plant adaption to soil nutrient limitations in karst ecosystems.
     
    Spatial and temporal variations of surface soil freezing days in Chang Tang Natural Reserve of Tibet during 1981-2018.
    DU Jun, ZHOU Kan-she, Ciwangdunzhu
    2020, 39(4):  1121-1129. 
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    The nearsurface soil freezing/thawing status is an important indicator of climate change. Based on the daily minimum surface soil temperature and air temperature data in the period 1981-2018 from five meteorological stations in Chang Tang Natural Reserve of Tibet (CTNRT), the spatiotemporal distribution of the number of freezing days for the ground surface under the scenarios of 1.5 ℃ and 2 ℃ warming were analyzed with the methods of linear regression method and MannKendall test. The results showed that: (1) In the past 38 years, the first date of nearsurface soil freeze had been significantly postponed at a rate of 7.72 d·10 a-1, and the last date of nearsurface freeze had been advanced at a rate of 8.17 d·10 a-1. The duration days and freeze days exhibited declining trends, with a rate of 14.69 and 11.19 d·10 a-1,respectively. The average rate of change for most near-surface freezing variables in CTNRT was generally higher than that over the Qinghai-Tibet Plateau. (2) In terms of inter-decadal variation, the first date had been delayed, as opposed to the advanced last date, while the duration days and freeze days had been shortened in CTNRT. (3) The trend reversal for the near-surface freeze parameters occurred in the early 21st century, with the abrupt point being later than thatover Qinghai Tibet Plateau. (4) The values of near-surface freeze parameters in CTNRT are similar under theRCP4.5/RCP8.5 scenarios of 1.5 ℃ warming: the first date is delayed by 25 days, the last date becomes earlier by 22 days, and the duration and freeze days are shortened by 46 and 28 days, respectively. Under the RCP4.5/RCP8.5 scenarios of 2.0 ℃ warming, the first date is postponed by 35 and 33 d, the last date is advanced by 30 and 29 d, the duration is shortened by 64 and 62 d, and the number of days is reduced by 40 and 39 d.
    Dynamics of water-soluble matters during leaf litter decomposition under different habitats in an alpine forest.
    LIU Bo-wen, ZHANG Li, WU Fu-zhong, NI Xiang-yin, XU Zhen-feng, TAN Bo, YUE Kai
    2020, 39(4):  1130-1140. 
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    Watersoluble matter (WSM) released during litter decomposition is an important source of carbon and nutrient in different forest aquatic and land habitats. Using litterbag method, leaf litter decomposition of four dominant species (i.e., Salix paraplesia, Rhododendron lapponicum, Sabina saltuaria, and Larix mastersiana) was examined in an alpine forest. We investigated the dynamics of WSM and water soluble carbon (WSC) contents and their related influencing factors during litter decomposition in stream, riparian zone, and forest floor at different periods (i.e., prefreezing period, freezing period, melting period, growing season, and late growing season). After two years of decomposition, we found that stream significantly promoted the release of WSM and WSC in leaf litter. The losses of WSM and WSC contents of the same litter species were significantly differed among different habitats (P<0.05), with stream>riparian zone>forest floor. The content of WSM decreased remarkably at the initial stage of decomposition. Across the whole decomposition process, changes in the contents of WSM (-70.43%) and WSC (-84.31%) showed a similar decreasing trend. In addition, the releases of WSM and WSC during leaf litter decomposition were significantly affected by decomposition period, litter species, and local environmental factors such as temperature, pH, and nutrient availability. These results suggested that WSM and WSC in decomposing leaf litter were easy to transfer to the downstream ecosystems with water flow. Environmental factors played an important role in the release of WSM and WSC during leaf litter decomposition, which provided useful information for our better understanding of material fluxes in alpine forests.
    Fractal and hydrophysical characteristics of soil particles in different forest stands in south subtropical China.
    LIN Li-wen, DENG Yu-song, YANG Gai-ren, XU Zhen-xin, LIU De-yang, WEI Guo-yu, HUANG Zhi-gang
    2020, 39(4):  1141-1152. 
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    Based on the theories and methods of soil fractal and forest hydrology, we examined soil particle composition and hydrophysical characteristics of six different forest types (Pinus massoniana forest, Cunninghamia lanceolata forest,Eucalyptus urophylla× E. grandis forest, Mytilaria laosensis forest, Castanopsis hystrix forest and natural secondary forest) in Nanning Stateowned Gaofeng Forest Farm of Guangxi. Clay was the main component of soil particles in the study area, followed by silt and fine sand particles, while the content of coarse sand particles was relatively low. The fractal dimension of soil particles ranked with following order: natural secondary forest, C. lanceolata forest, M. laosensis forest, C. hystrix forest, P. massoniana forest andE. urophylla ×E. grandis forest. There were significant differences in soil hydrophysical characteristics across different forest types. Water storage capacity was following the order of natural secondary forest, M. laosensis forest, C. lanceolata forest,C. hystrix forest,P. massoniana forest, and E. urophylla×E. grandis forest. Moreover, water storage capacity of surface soil layer (0-10 cm) was better than that of lower layer (20-50 cm). The fractal dimension of soil particles was mainly affected by clay content. Fractal dimension had a significant positive correlation with clay content, total porosity and saturated water storage, and a significant negative correlation with soil density. There was no significant relationship between fractal dimension and noncapillary porosity, noncapillary water storage, and organic matter content. The fractal dimension of soil particle distribution can be used as a comprehensive index to reflect the soil hydrophysical properties of forest plantations in the subtropical red soil area.
    Effects of labile organic carbon application rates on the priming effect at different soil depths in an evergreen broadleaved forest of Wuyi Mountain.
    QIU Qing-yan, YANG Yu, WANG Hao, HU Ya-lin
    2020, 39(4):  1153-1163. 
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    The mineralization of soil organic carbon (SOC) plays an important role in soil carbon and nitrogen cycling. Inputs of labile organic C can stimulate or mitigate SOC mineralization through positive or negative priming effect. While previous studies on the effects of the amount of labile organic carbon input on soil priming effect focused more on the topsoil, less attention has been paid to the deep soil. We carried out a 13C labeling experiment to investigate the effects of labile organic carbon input on the priming effect at topsoil and subsoil layers which were collected from an evergreen broadleaved forest in Wuyi Mountain. We examined the changes in microbial community composition and soil available N content to clarify the underlying mechanisms. The results showed that the input of glucose inhibited SOC mineralization (i.e., a negative priming effect), but the priming magnitude  varied across different amounts of glucose input and soil depths. The magnitude increased with the amount of glucose input for topsoil, but remained stable in deep soil. Moreover, glucose input had no significant effect on soil microbial biomass and community composition (i.e., total PLFA content, bacteria, fungi, actinomycetes, and the ratio of bacteria to fungi). The magnitude of priming effect was not dependent on the amount of glucose input and microbial community composition, but dependent on soil available nitrogen content, which accounted for 90.8% and 63.4% of the variation in the magnitude of priming effect for the topsoil and subsoil, respectively. Glucose input led to a decline in soil available N, but was not associated with microbial N immobilization, indicating that soil available N can meet microbial demands. The negative priming effect observed in this study might be attributed to preferential substrate utilization.
    Spatial and temporal distribution of soil conservation and its driving forces in the Three Gorges Reservoir Area.
    TIAN Yu, ZHU Jian-hua, LI Qi, FENG Yuan, LI Chen-yu, XIAO Wen-fa
    2020, 39(4):  1164-1174. 
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    Combining ArcGIS with the Universal Soil Loss Equation (RUSLE), we examined the temporal and spatial dynamics of soil conservation in the Three Gorges Reservoir Area (TGRA) from 1990 to 2015, and analyzed the effects of climatic, hydrologic, topographic, and social factors on soil retention. The mean annual soil conservation was 5.79×109 t (1004.23 t·hm-2) in the TGRA during 1990-2015. Soil conservation services in forests, shrubs, grasslands, cropland, and unused land were successively declined. In the past 25 years, the value of soil conservation per unit area in the TGRA fluctuated within the range of 818.73-1280.50 t·hm-2, with the highest value in 2000. The soil conservation service was higher in the northeast but lower in the southwest, the bank area of the Yangtze River, and the main urban area of Chongqing. Soil holding capacity first increased and then decreased with increasing altitude, with the strongest capacity in the areas of 1000-1500 m above sea level. Soil holding capacity gradually increased with the slope. Elevation, slope, annual precipitation, and vegetation cover contributed greatly to changes in soil retention. Anthropogenic disturbance was the main driving force for changes of soil retention. Therefore, it is necessary to strengthen ecological protection and restoration, implement coordinate management, reduce anthropogenic disturbance, in order to improve the ecologicalsecurity in the TGRA.
    Effects of different improvement regimes on organic carbon pools of soils newly developed from parent material of Mollisols.
    YUAN Ya-ru, HAN Xiao-zeng, LI Na, YOU Meng-yang, ZOU Wen-xiu
    2020, 39(4):  1175-1182. 
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    The fractionation technique of aggregate and occluded microaggregate was used to separate soil organic matter into three carbon (C) fractions: total coarse particulate organic matter (total cPOM) as labile C pool, total fine particulate organic matter (total fPOM) as slow C pool, and total silt and clay particles (total S&C) as passive C pool. We examined the effects of different management practices on soil organic C (SOC) pools after 8-year soil development from parent material of Mollisols, aiming to provide reference for the rapid restoration of soil fertility of seriously eroded black soil. There were six treatments: no-tilled vegetation restoration under natural fallow (NatF), no-tilled vegetation restoration under alfalfa plantation (Alfa), tillage under corn-soybean cropping system without chemical fertilizers application (F0C0), tillage under corn-soybean cropping system with chemical fertilizers application (F1C0), tillage under cornsoybean cropping system with chemical fertilizers plus fixed amount of maize straw and simulated organic manure (F1C1), tillage under corn-soybean cropping system with chemical fertilizers plus all biomass (all crop shoots, roots and seeds) returned (F1C2). The results showed that SOC pools (total C pool, labile C pool, slow C pool, and passive C pool) in all treatments were significantly improved after 8year soil development from parent material of Mollisols. F1C2 and F1C1 had the highest SOC content among all the treatments. Compared with NatF, SOC contents in F1C2, F1C1 and Alfa treatments were increased by 60.7%, 41.2% and 18.2%, respectively. There was no significant difference in SOC content between NatF and F0C0 or F1C0 treatments. The C contents in total cPOM, total fPOM and total S&C in F1C2 and F1C1 treatments were significantly higher than that in other treatments. F1C2 had higher C contents of the three C fractions than F1C1. Compared with NatF, the increment of C in Alfa treatment was mainly attributed to the enhancement of C in total S&C. There was no significant difference in C contents in total fPOM and total S&C between NatF and F1C0 or F0C0 treatments. The C content in total cPOM in F1C0 and F0C0 treatments was significantly lower compared with NatF. These results suggested that higher amount of C input combined with chemical fertilizer in agricultural ecosystem of black soil under corn-soybean rotation and traditional tillage systems could increase both labile and recalcitrant C pools, which could accelerate the improvement of parent material of Mollisols and thus be an effective measure to improve soil organic matter in seriously degraded black soil region.
    Effects of biochar addition on the availability of heavy metals and soil quality in red paddy soil.
    WEN Xin, CHEN Xiao-min, GUO Bi-lin, JING Feng, HU Shi-min, LI Lian-qing
    2020, 39(4):  1183-1190. 
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    A field experiment was conducted to examine the impacts of biochar addition on soil physicochemical properties, concentrations of heavy metals, and soil quality of a red paddy soil in Hunan Province, China. Biochar was added at dosage of 0, 10, 20, 30, and 40 t·hm-2 before the rice was transplanted in 2017. Soil samples in tilled layer (0-17 cm) and plow solelayer (17-29 cm) were collected in September 2018. Soil quality was evaluated by soil quality index (SQI). The results showed that biochar addition reduced soil bulk density but increased soil porosity, soil pH, the concentrations of organic matter and dissolved organic carbon (DOC). The contents of ammonium and available phosphorus were the highest at the treatments of 10 and 30 t·hm-2. Biochar addition enhanced the activities of soil urease, catalase and sucrose. The concentrations of cadmium (Cd), arsenic (As) and lead (Pb) in the red paddy soil werereduced by biochar addition, especially at the 40 t·hm-2 treatment. The concentrations of heavy metals and their influence factors were analyzed by stepwise regression. In the tilled layer, the contents of available Cd, As and Pb were significantly correlated with urease activity, soil pH, and sucrose activity, respectively. However, the contents of available Cd, As and Pb were significantly correlated with urease, catalase activities and available phosphorus content in the plow sole layer, respectively. The values of SQI among treatments decreased in the order: A40>A30>A20>A10>CK, with corresponding value of 0.641, 0.638, 0.579, 0.533, and 0.464, respectively. This result indicates that the quality of red paddy soil was the highest at the application amount of biochar is 40 t·hm-2. In conclusion, biochar addition can effectively reduce the availability of heavy metals and improve soil quality.
    Effects of plastic film mulching and organic manure application on  C， N， P stoichiometry of soil and crop.
    WANG Qing-lu, ZHU Peng-fei, DING Fan
    2020, 39(4):  1191-1197. 
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    To examine the effects of plastic film mulching and organic manure application on C, N, and P stoichiometry of soil and crop, we collected soil and corn tissues (root, stem, leaf, and seed) in 2015 from a longterm experiment at Shenyang Agricultural University, which was initiated in 1987. We measured C, N and P concentrations in soil and crop tissues. Results showed that the main and interactive effects of long-term film mulching and manure application on soil pH were statistically significant. Film mulching did not affect soil C, N, P, available N and P concentrations, and soil C∶N∶P ratios (P>0.05). Manure application significantly increased soil total C, N, P, available N, and available P concentrations (P<0.01), and significantly decreased soil C/P and N/P ratios (P<0.01). Film mulching did not affect the stoichiometry of C, N, and P in all plant tissues except for leaf N and seed P concentration and C/P ratio. Organic fertilizer application significantly increased N concentration and decreased C/N ratios in all tissues (P<0.05). Manure application increased root and seed P concentrations (P<0.05) and decreased seed C/P ratio (P<0.001). In conclusion, soil and crop C, N, and P stoichiometry could be affected by long-term organic fertilizer application but not by plastic film mulching.
    Screening of straw degrading microbial strains and their degradation effects.
    MA Xin-yu, SUN Li-na, LU Shan, HE Peng, ZHOU Yi-ping, LIU Xing-yi
    2020, 39(4):  1198-1205. 
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    Improper disposal of crop straw might have negative effects on rural ecological environment. At present, the main way of straw disposal in Northeast China is to smash and return the straw to the field directly. However, the straw is not easily decomposed in natural environment, which affects the spring ploughing. Therefore, it is important to find new types of culturable strawdegradation bacteria from the perspective of adding exogenous microorganisms to promote straw insitu decay. In this study, the potential highefficiency cellulose degrading bacteria were isolated and screened from the rotten straw and cattle intestines by enrichment culture, primary screening of Congo red culture medium, and disintegration test of filter paper. The optimum growth temperature and pH were assessed. The actual degradation ability of the strains was investigated in liquid fermentation culture. Five strains with high degradation ability of corn straw were obtained. The growth peaks of the five strains occurred in the range of temperature 20-30 ℃, pH 7.5-8.5. After 15 days of liquid fermentation, the weight loss rate of straw by the five strains was in the order of NX9 (53.88%) > NF6 (51.36%) > JF3 (46.97%) > JZ8 (45.2%) > JX4(35.79%)> CK (23.88%). Among them, strain NX9 (temperature 30 ℃, pH 7.5) had the strongest degradation ability to straw hemicellulose and lignin, with the degradation rate of 48% and 37.7% in 15 days, respectively. Strain NF6 and JF3 belong to cold resistant bacteria. Especially, strain NF6 can grow and propagate at 4 ℃. Our results provide a basis for developing the technology of “exogenous microorganism promoting straw in situ decay” in northern China.
    Feeding rhythm of Anoplophora chinensis (Coleoptera: Cerambycidae) adults and their behavioral responses to two kinds of crude extracts from Melia azedarach.
    PENG Han, LIU Ya-lin, GENG Xian-sheng, FANG Lin-xin, ZHANG Shou-ke, ZHANG Wei, SHU Jin-ping, WANG Hao-jie
    2020, 39(4):  1206-1213. 
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    Anoplophora chinensis Forster is one of the most serious wood-boring pests. Behavioral manipulation is an important way to control the beetle. Aiming to develop an effective “attract and kill” strategy with plant-derived attractant against the beetle, feeding behaviors ofA. chinensis adultswere observed and the alluring effects of different kinds of extracts of Melia azedarach L. were examined. The results showed that feeding behavior ofA. chinensis existed both in the light and dark (15L∶9D), with no significant difference in feeding consumption between light and dark (P>0.05). In the light, peak feeding period of female adult A. chinensis was from 13:00 to 14:30, but there was no feeding peak of the male. In the laboratory, crude oil by Soxhlet extraction was more attractive to adult A. chinensis than that by steam distillation. Adult A. chinensis settled significantly more time on the filter paper treated with crude oil by Soxhlet extraction (15.19±2.09 min) than that treated with crude extract by steam distillation (8.94±1.26 min, P<0.05). Adult A. chinensis could be trapped by both extracts in forests. There was no significant difference between the number of beetles trapped by the two kinds of extracts (P>0.05), with 3.0±1.15 beetles being captured with the crude oil by Soxhlet extraction per trap and 2.0±0.58 adults being captured with the crude extract by steam distillation per trap.
    Effects of AM fungi on alfalfa leaf spot caused by Phoma medicaginis and pea aphids Acyrthosiphon pisum.
    Li Ying-de, Duan Ting-yu
    2020, 39(4):  1214-1221. 
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    The leaf spot caused byPhoma medicaginisis a common disease of alfalfa, which usually cooccurs with pea aphid (Acyrthosiphon pisum). To clarify the regulation role of AM fungi, we investigated the defense mechanism of AM fungiinoculated plants after infected byP. medicaginis, and the subsequent damage of pea aphids to plants. The results showed that AM fungi significantly reduced plant disease index (P<0.05). AM fungi regulated the response of plants to leaf spot and aphids by promoting plant growth (P<0.05), changing activities of plant defensive enzyme superoxide dismutase (SOD) and catalase (CAT) and the concentrations of salicylic acid (SA) concentration (P<0.05). Infection of pathogen enhanced the activities of plant antioxidant defense system, including peroxidase (POD), SOD, CAT and PPO (P<0.05), thereby increasing the resistance of plants to subsequent aphids feeding. AM fungi played an active role in defence against pathogen, significantly increased the SOD and CAT activities (P<0.05), and inhibited the damage of leaf spot by P. medicaginis. The aphids further aggravated plant damage and reduced the regulative role of AM fungi and the resistance of alfalfa to pathogen infection.
    Effects of nitrogen level on population dynamics of adult Q-typeBemisia tabaci from tomato seedlings.
    HE Yun-chuan, SONG Xian-mei, LI Nan, WANG Xin-pu, XIN Ming, JIA Yan-xia
    2020, 39(4):  1222-1230. 
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    Bemisia tabaci is a major agricultural pest. To reduce the application of chemical pesticides, it is important to take ecological controlling measures for cultivation management. Here, we investigated five agronomic traits of tomato seedlings and Q-type B. tabaci population for nine times in greenhouses. Our aim was to probe into the relationship of B. tabaci population density from tomato seedlings and nitrogen levels (i.e., 1134 mg·L-1, high; 945 mg·L-1, standard; 756 mg·L-1, low) by using principal component analysis, linear regression analysis, and Pearson correlation analysis. The results showed that the five traits including plant height, stem diameter, leaf area, chlorophyll relative content, and leaf total nitrogen content followed a similar trend with the order of high nitrogen level > standard nitrogen level > low nitrogen level. The population density of B. tabaci from tomato seedlings at the peak stage for nine times showed the same order of high nitrogen level > standard nitrogen level > low nitrogen level. The results of linear regression analysis and Pearson correlation analysis showed a high correlation between B. tabaci population density and the chlorophyll relative content and leaf total nitrogen content. The results of principal component analysis showed that leaf chlorophyll relative content was the key factor driving B. tabaci population density across nitrogen levels. It was suggested that nitrogen level was one of key factors affecting the growth of tomato and B. tabaci population density: the higher nitrogen level, the better growth of tomato seedlings and the greater density of B. tabaci. Leaf total nitrogen content and chlorophyll relative content were suggested to be the ecological control index to monitor the fluctuation of Q-type B. tabaci population density.
    Daily and seasonal variation of activities of Tibetan Macaque (Macaca thibetana) based on infrared camera trapping.
    LIU Bang-you, WANG Cheng, ZHANG Ting-yue, LIANG Sheng, SU Hai-jun, ZHANG Ming-ming, ZHOU Da-qing, HU Can-shi
    2020, 39(4):  1231-1237. 
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    The dynamics of daily activity are the activity intensity and periodic change pattern of animals in different periods of the day, which are closely related to metabolism control and energy expenditure cost. From August 2015 to August 2017, the daily activities of Macaca thibetana in different seasons were examined in Chishui Alsophila National Nature Reserve, with infrared camera monitoring. A total of 105 independent pictures of M. thibetana(out of 687 recognizable pictures) were collected with a sampling effort of 6370 camera-days. The analysis of daily activity patterns showed that M. thibetanawas a typical diurnal animal, with daily activity peaks at 12:00-16:00 with the shape of ‘M’. There was no significant difference of daily activity between rainy and dry seasons (P>0.05). In dry season, daily activity time was decreased in the sunrise period and the activity peaks delayed from midday to afternoon as compared to rainy season. Temperature range of daily activity was -2 to 34 ℃ along with the change of annual temperature, among which 15-25 ℃ accounted for 59%. Our results reveal the seasonal variation of daily activity patterns of M. thibetana based on the infrared camera and provide scientific basis for the indepth understanding of the behavioral ecology ofM. thibetana.
    Functional and phylogenetic diversity of birds in urban habitat patches in Macao, China.
    2020, 39(4):  1238-1247. 
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    Understanding how communities assemble is a central and fundamental question inecology, which is critical for explaining species coexistence and maintenance of species diversity, and for improving biodiversity conservation practice and policy. Compared with species diversity (species richness and other species diversity indices), functional and phylogenetic diversity consider the differences of species in traits and evolutionary history that closely correlated with ecosystem services and functioning, providing insights into the mechanisms driving community clustering or overdispersion. We used line transects to collect data on bird species richness andabundance in five urban habitat patches in Macao, China (Ecological Zone I: STQ；Lu’niaolin: LNL; tidal flat wetland nearby Saimachang: SMC; tidal flat wetland nearby port: GZ; mangrove forest under Lianhuaqiao: LHQ) from May 2014 to January 2017. Surveys were conducted during the breeding season in 2014, 2015, and 2016, and during the wintering season in 2014, 2015, 2017, and were repeated for 14 times. Species diversity was estimated as species richness and abundance, while functional and phylogenetic diversity were estimated using functional richness (FRic) and Faith’s PD, respectively. Abundance weighted mean pairwise functional distance (MFD) and mean pairwise phylogenetic distance (MPD) were calculated to evaluate changes in the functional and phylogenetic structure of bird community, respectively. The results were as follows: (1) A total of 98 bird species were recorded, belonging to 14 orders and 32 families. Passerines and Ardeidae had the highest species richness (15 and 11 species, respectively). In addition,Egretta garzetta was the most abundant species (849 individuals). (2) Bird species richness (PD and MPD) was the highest in STQ (species richness was 68), whereas abundance was the highest in LHQ (2940 individuals), FRic and MFD was the highest in SMC. (3) Patch area was important factor in explaining the richness, abundance, FRic and PD of birds, whereas vegetation area and tidal flat area had important effects on MFD and MPD, respectively. (4) SES.MFD were significantly clustered in GZ and LHQ, and SES.MPD were significantly clustered in LNL and LHQ, indicating that functional clustering occurred in GZ and LHQ might be a result of environmental filtering. Taken together, our findings suggest that the differences in habitat characters lead to changes in community assembly mechanisms, which is difficult to provide by just considering species diversity. Our results highlight that the necessity of integrating multiple dimension of biodiversity.
    Understory seed removal of Chinese yew (Taxus chinensis) by rodents and ants in patchy habitats.
    LI Ning, ZHANG Na, XU Jing-wen, BAI Bing, LU Chang-hu
    2020, 39(4):  1248-1253. 
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    Chinese yew (Taxus chinensis) is an endangered species and prone to extinction in China. While the contribution of birds to the recruitment of bird-dispersed trees, the effects of post-dispersal seed removal by rodents and ants were overlooked. In this study, we investigated post-dispersal seed removal by understory animals for T. chinensis in a seed placement experiment. Seven species (four rodent species, i.e. Callosciurus pygerythrus, Tamiops swinhoei, Rattus tanezumi, Niviventor confucianu and three ant species i.e. Aenictus bobaiensis, Monomorium floricola, Odontomachus monticola) could remove seeds in the ground. Seed removal by rodents was the main factor for the disappearance of T. chinensis seeds, with seed disappearance rate varying among patches and edge habitats. Mother tree forest and bamboo forest were main foraging habitats for rodents, with feeding rate in both habitats being significantly higher than that in pecan plantation. The edge habitats were corridors instead of foraging fields for rodents. Callosciurus pygerythrus presented frequently in habitats outside the mother tree patch. For other species, habitat fragment preferred mother tree patch and bamboo forest but evaded pecan plantation. Seed removal by rodents could reduce the density of seed bank in the bamboo patches, thus affect recruitmentof T. chinensis. Our results highlight the importance of understory seed removal in the plant recruitment in the patchy environment.
    Fish community structure and diversity in Daya Bay in summer.
    XU Shan-nan, GUO Jian-zhong, FAN Jiang-tao, XU You-wei, LI Chun-hou
    2020, 39(4):  1254-1264. 
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    We investigated the composition, diversity, and structural characteristics of fish resources in summer in Daya Bay, South China Sea, based on data collected from one otter trawl survey in August 2018. The results showed that 56 species were collected in 2018, belonging to 47 genera, 34 families, and 9 orders. Among them, species of Perciformes (39 species) were predominant, accounting for 69.64% of the total species richness. Dominant species included Leiognathus brevirostris, Siganus oramin, Parachaeturichthys polynema,Polynemus sextarius, and Evynnis cardinali, which are lowvalue fish with small stature. There was significant spatial variation in fish species diversity, with the greatest value in the mouth area, followed by that of the coastal waters, and the lowest in the central area. The fish community structure could be roughly divided into two groups: bay type with brackish water and bay mouth type with seawater. Compared with the summer survey data of 1985-2017, fish species diversity in the Daya Bay had been decreased over the past 30 years. The compositions of dominant fish species had been changed significantly, from large-stature pelagic economic fish to small-stature and low-value fish in bottom and near-bottom layer. The main reason for such changes was anthropogenic disturbance, especially the fishing activities, which led to simpler fish community structure.
    Antarctic krill (Euphausia superba) aggregation types and affecting factors around the South Shetland Islands, Antarctic during austral summer-autumn 2018.
    ZHU Guo-ping, LI Hui-ting, LI Ye, YANG Yang
    2020, 39(4):  1265-1272. 
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    As a typical aggregating marine organism, aggregation characteristics of Antarctic krill (Euphausia superba) is an important part of behavioral ecology researches. Antarctic krill are distributed around the South Shetland Islands with high density. The mechanistic explanations of the shape and size of Antarctic krill aggregation remain controversial. The acoustic data of Simrad EK80 collected from the water around the South Shetland Islands were analyzed using Echoview V6.16. Antarctic krill aggregations were classified into 13 types. The effects of environmental (sea surface temperature and sea condition) and spatialtemporal variables on aggregation type were examined by principal coordinate analysis (PCoA). The results showed that sea condition (wave) was the most important fact affecting the aggregation type of Antarctic krill, followed by the illumination intensity. Patched smallsized aggregation had a wide distribution at the spatialtemporal level, with higher proportion both at night and daytime (>30%). Smallsized aggregation often occurred during the daytime, whereas largesized aggregation occurred at night. Krill aggregation in February was significantly associated with sea condition and latitude, significantly associated with brightness in March, and significantly associated with both brightness and sea condition in April.
    Deposition characteristics of microplastics in benthic animals from the main estuaries of Poyang Lake.
    JIANG Wei-qun, LIU Shu-li, JIAN Min-fei, HU Qi-wu
    2020, 39(4):  1273-1280. 
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    Microplastics are a kind of widespread environmental contaminants, with serious threat to aquatic environment. In this study, three benthic species (Corbicula fluminea, Unio douglasiaeand Cipangopaludina cahayensis) were sampled from the estuary of Raohe River to Poyang Lake and the estuary of the middle tributary in lower Ganjiang River to Poyang Lake. The samples were screened by tissue digestion, and then filtered through the filter membrane. The membranes were dried and observed under metallographic microscope to identify plastic fragments. The abundance and types of microplastics in the benthic animals were analyzed. Microplastic deposition was found in all the three benthic species, particularly in their digestive tracts, with their deposition abundance descending as follows: C. fluminea >C. cahayensis >U. douglasiae. The microplastics deposited in the three benthic species can mainly be divided into four types, including particles, chips, films, and fibers, with fibers being the dominant type. The dominant colors of the microplastics were transparent, blue, red, and purple. The abundance of microplastics with particle size less than 1 mm was the highest. The microplastic abundance in the benthic animals decreased with increasing particle size. Spatially, the microplastic abundance of benthic species from the estuary of Raohe River to Poyang Lake was higher than that from the estuary of the middle tributary in lower Ganjiang River. It is concluded that the microplastic pollution in Poyang Lake has resulted in microplastic deposition in benthic species. More attention therefore should be paid on controlling the intake of aquatic products from the lake. In comparison with other studies, the microplastic pollution of benthic animals in this study is at the medium level.
    Assessment of ecosystem health in the Dulong River.
    AO Si-cheng, HU Jian-cheng, LI Xian-fu, TAN Lu, YE Lin, CAI Qing-hua
    2020, 39(4):  1281-1287. 
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    We investigated river physical habitat, water physicochemical properties, and benthic macroinvertebrates in the main and tributaries of the Dulong River from October to November 2018. Based on the characteristics of the Dulong River, we developed a comprehensive assessment index of river ecosystem health to evaluate its ecosystem health. The results showed that 85.2% of the sites in the survey were in health status. The sites near the densely populated towns were at the status of sub-health. Specifically, the worst unhealthy sites were found in the Dulongjiang Township with the most developed tourism industry. Rivers are important carrier of freshwater resources. Under the background of continuous development of tourism, a scientific-evaluation of river health status can provide scientific basis for ecosystem restoration, rational exploitation and utilization of water resources, and sustainable development of Dulong River.
    The chemical weathering characteristics of different lithologic mixed small watersheds in Southwest China.
    CHEN Shuai, ZHONG Jun, LI Cai, WANG Wan-fa, XU Sen, YAN Ze-long, LI Si-liang
    2020, 39(4):  1288-1299. 
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    Chemical weathering affects global carbon cycle and climate change, and thus the rates and controlling factors of which are research hotspots. To explore the chemical weathering rates and their influencing factors in basins with different rock lithology, we collected river water samples and analyzed hydrochemical characteristics in the Yinjiang River basin, Shiqian River basin and Yuqing River basin in September 2018. The results showed that the average total dissolved solids (TDS) in river water was 244 mg·L-1, which was much higher than global mean value (100 mg·L-1). The spatial difference in TDS values showed that the lithologic distribution caused a large variation in ion concentration. The most abundant anion and cation in basins were HCO3- and Ca2+, respectively, indicating that the weathering of carbonate rock in these basins played a leading role in river water chemistry. The forward model was used to estimate the contribution of different endmembers (atmosphere, anthropogenic activities, silicate rock, and carbonate rock) to the total dissolved cations in the river. We found that the contributions of carbonate rocks in the tributaries showed significant variations (55.0%-93.9%), which was mainly affected by lithology distribution. The silicate weathering rates in Yinjiang River, Shiqian River and Yuqing River were 4.4, 2.8 and 2.5 t·km-2·a-1, and the corresponding CO2 consumption rate was 45×103, 18×103 and 16×103 mol·km-2·a-1, respectively. The carbonate weathering rates were much higher, being 43.7, 24.7 and 29.8 t·km-2·a-1 for the Yinjiang River, Shiqian River and Yuqing River respectively. The corresponding CO2 consumption rates for the threerivers were 498×103, 284×103 and 354×103 mol·km-2·a-1, respectively. The spatial variations of weathering under the same climatic conditions highlighted the importance of lithology on chemical weathering. Our results suggest high spatial variations of chemical weathering under various lithologic conditions, which can be used for assessing regional water environmental quality and its effect on global carbon cycle.
    Dynamic stability of sand-accumulation belt along the upwind edge of Minqin Oasis.
    CHANG Zhao-feng, ZHU Shu-juan, ZHANG Jian-hui, ZHAO Peng, DUAN Xiao-feng
    2020, 39(4):  1300-1308. 
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    Drifting sand accumulation belts are formed after 60 years of desert control along the edge of the upwind direction of the oasis in Hexi Corridor, Gansu Province. Among them, the sand accumulation belts on the edge of the upwind direction of Minqin oasis are the largest and most continuous. To reveal the stability dynamics of sand accumulation belts, 11 sampling lines were set on the upwind edge of Minqin oasis, with which we observed wind erosion/sand accumulation and characteristic points of sand surface displacement for seven times from early November 2016 to early April 2019. The sand accumulation belts on the edge of upwind direction of Minqin oasis could be divided into three types based on their formations: Sand accumulation belt of artificial sand-fixing forest, of natural shrub, and of tree-shrub mixed single-row forest. Wind erosion is the most serious and the forward moving speed is the fastest in the sand accumulation belt of artificial sand-fixing forest, followed by that of natural shrubbery. The lighter the degree of wind-erosion on the sand surface, the slower the sand accumulation belt moves forward. The higher the coverage of herbaceous plants, the lighter the degree of wind erosion on the sand surface, and the more slowly the sand accumulation belt moves forward. The coverage of herbaceous plants and the stability of sand surface complement each other. The windward slope of sand accumulation belt is wind erosion surface, while leeward slope is sand accumulation surface. One side of wind erosion and the other side of accumulation maintain the forward movement and dynamic stability of sand accumulation belt.
    Spatial relationship of greenspace landscape pattern with land surface temperature in three cities of southern Fujian.
    SHEN Zhong-jian, ZENG Jian, LIANG Chen
    2020, 39(4):  1309-1317. 
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    Exploring the effects of greenspace landscape pattern on thermal environment is of great significance to improving urban ecological environment. Based on Landsat remote sensing data in Xiamen, Zhangzhou and Quanzhou of southern Fujian, landscape ecology and spatial autocorrelation theory were used to quantify spatial distribution characteristics of greenspace landscape and land surface temperature. Further, we used bivariate spatial autocorrelation and spatial autoregressive model to analyze the spatial relationships. The results showed that both of greenspace and land surface temperature had significant spatial autocorrelation. In the inland areas with high elevations, greenspace was significantly concentrated with relatively low land surface temperature, while in urban areas, towns and large areas of cultivated land, greenspace was less distributed and relatively high land surface temperature. Greenspace landscape pattern had stronger effects on the land surface temperature in Zhangzhou and Quanzhou than in Xiamen. The percentage of landscape, largest patch index, aggregation index and mean patch area of greenspace were negatively correlated with land surface temperature, whereas patch density was positively correlated with land surface temperature. The correlation between edge density, mean shape index and land surface temperature is uncertain. Spatial lag model and spatial error model performed better in explaining the spatial relationship between greenspace landscape pattern and land surface temperature.
    Spatial variation of forest litter nutrients and its controlling factors.
    QIN Qian-qian, WANG Hai-yan
    2020, 39(4):  1318-1329. 
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    Litter, as a principal resource for improving forest quality, plays a major role in the sustaining of ecosystem function, including nutrient return, soil and water conservation, toxic substances filtration, food resource of animals and microorganisms, seed germination, keeping temperature and humidity of surface soil. Spatial variation of litter nutrients refers to the difference and diversity of litter nutrients in different spatial locations within a certain region, which could affect community distribution and is a common but very important feature in forest ecosystems. Here, we reviewed the spatial variation of forest litter nutrients and its relationship with natural and anthropogenic factors. Current research on the spatial variation of forest litter nutrients gave priority to the two quantitative description methods (classical statistics and geostatistics), involved community, landscape, regional, and global scales, and related to factors such as plant, soil, terrain, climate, forest structure, and disturbances. The results of spatial variation of forest litter varied with methods, objects, purposes, research areas or scales of different studies. Therefore, we need to strengthen studies on the standardization and comprehensive application of quantitative methods and select appropriate methods to describe spatial variation. It is worthy to investigate the spatial variation of forest litter and its relation to environmental factors at multiplescale for the determination of research scales and corresponding affecting factors.
    Research advance of mangrove wetlands models.
    2020, 39(4):  1330-1337. 
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    Mangroves, forested wetland ecosystems located along the coasts, have various ecological functioning including reducing the energy of wind and current, protecting coastlines, and sequestering carbon dioxide to mitigate global climate change. Due to the special geographicalenvironmentof their habitats, studies on mangrove wetland model are still limited compared to inland wetland. To promote the researches on mangrove wetland models, we classified current models in mangrove studies into three types based on their function, including vegetation growth and production models, hydrological models, and material and energy flow models. We further reviewed the research progress of related models. We proposed that: (1) the effectiveness of current mangrove wetland models in different regions and scales should be further verified, and (2) further investigation should focus on model researches related to ecosystem services and vegetation restoration projects.
    Research progress on “methane paradox” phenomenon in lake surface waters.
    2020, 39(4):  1338-1348. 
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    The traditional paradigm in aquatic sciences holds that microbial methanogenesis happens primarily in the anoxic conditions. The widely reported paradoxical supersaturation of CH4 in oxygenated surface waters challenges such traditional paradigm. Here, I summarized two new concepts in literature, i.e, external source hypothesis and insitu produced hypothesis, to explain the “methane paradox” phenomenon. The former supports that the lateral input of CH4 is from the surrounding littoral zone (FL), which could be important for small lakes with an organic-rich littoral zone. The latter believes in-situ production in the oxic surface waters (P), which accounts for large, deep lakes in the valleys. The external inputs from the upstream rivers (FR), turbulent diffusion from the sediments and metalimnion layers (FZ), the dissolution of bubbles (FD) are all contributed to the supersaturated CH4 concentrations in the oxic surface layers. CH4 emission flux at the airwater interface (E) and CH4 oxidation (O) can lead to CH4 loss in the oxic surface layers. The construction of CH4 mass balance model will be helpful for understanding the supersaturation of CH4 in oxygenated surface waters. Actually, the supersaturated CH4 concentration in the surface waters is related to environmental characteristics of lakes. However, differences in data analysis methods, sampling periods, and lake environments can result in the debates of two hypotheses.
    Advances in research on the effects of testosterone on bird breeding.
    DONG Fei, WAN Dong-mei, WANG Juan
    2020, 39(4):  1349-1355. 
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    Steroid hormone testosterone is one of the most important sex hormones affecting bird reproduction, which is closely related to breeding behavior. Testosterone affects sexual selection by changing feather color, song and so on. Meanwhile, testosterone could regulate the tradeoff between sexual selection and reproductive input. Testosterone affects reproductive efficiency, including nestling size, fledging size, and hatching success rate. Testosterone also affects the immune activity and survival rate of individuals. Most studies of bird breeding are based on exogenous implantation of testosterone. The results from literature had no consensus. The changes of testosterone level under natural conditions and the influencing factors are not well understood. The effects of testosterone on the reproductive process differed between male and female birds. Further studies on the effect of testosterone on breeding birds are critically needed.
    Comparison of different methods for determining plant water sources based on stable oxygen isotope.
    ZHANG Yu, ZHANG Ming-jun, WANG Sheng-jie, GUO Rong, CHE Cun-wei, DU Qin-qin, MA Zhuan-zhuan, SU Peng-yan
    2020, 39(4):  1356-1368. 
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    Using stable isotope technique to determine the sources of plant water is essential to improve our understanding of ecohydrological process and ecological management in arid and semiarid regions. There are many methods for determining plant water sources using stable isotope technique, but few studies have tried to compare outcomes of different methods. Based on empirical data, we used direct comparison method, multivariate linear mixed model (IsoSource), Bayesian mixing models (MixSIR, MixSIAR) and water absorption depth model, analyzed the water sources of vegetation, and compared the merit and demerit of each method. The results showed that Bayesian mixing models (MixSIR, MixSIAR) performed better in water source apportionment than IsoSource. The Bayesian models have higher requirements for data. The smaller the standard deviation of isotopic composition of vegetation xylem water and potential water source, the higher the reliability of model operation results. Bayesian hybrid model (MixSIR) is the optimal solution in this study. When determining plant water source by stable isotopes of hydrogen and oxygen, the potential water source of vegetation can be determined by direct comparison method. Furthermore, the contribution rate and range for each potential water source of plants could be calculated by the multivariate linear mixed model (IsoSource), and Bayesian mixing models (MixSIR, MixSIAR). When needed, the optimal model of quantitative analysis of plant water sources should be selected by evaluating the performance of models. If plant mainly absorbs soil water at different soil depths, the average depth of soil water absorbed by plants can be calculated by combining water absorption depth model. This study provides theoretical basis for the selection of method for identifying plant water sources by isotope techniques in arid and semiarid regions.
    Comprehensive evaluation of plough layer structuring effect based on radar chart method.
    BAI Wei, SUN Zhan-xiang, ZHANG Li-zhen, ZHENG Jia-ming, FENG Liang-shan, CAI Qian, XIANG Wu-yan
    2020, 39(4):  1369-1376. 
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    Improving plough layer structuring is an effective approach to solve the problems of shallow, compacted and lacked plough layer, which is of great significance to reasonable plough layer construction and soil health development of drylands in north China. To examine the effects of plough layer structuring of rainfed croplands, we designed an experiment with four treatments including up loose and down compaction plough layer (ULDC, as a control), furrow loose and ridge compaction plough layer (FLRC), all loose plough layer (AL) and all compaction plough layer (AC) in a longterm experimental station in Fuxin of Liaoning Province from 2015 to 2016. We measured nine parameters, including yield, water use efficiency, biomass, leaf area index, photosynthetic rate, soil bulk density, soil threephase structure distance, root weight density, root surface area density. According to the comprehensive evaluation function of vectors, comprehensive evaluation values of FLRC, AL, AC and ULDC were 0.8222, 0.7174, 0.6903 and 0.6455, respectively. After comprehensive analyses, FLRC is the best structure of the plough layer in the drylands of northern China. Our results provide a theoretical and technical reference for establishing a scientific soil tillage system and soil sustainable development in the region.
    Predicting spatial distribution of cation exchange capacity in silt loam soil under Lycium barbarum of Zhongning, Ningxia.
    BAO Wei-bin, BAI Yi-ru, YANG Fan, ZHONG Yan-xia, XIA Zi-shu, WANG You-qi
    2020, 39(4):  1377-1386. 
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    Soil cation exchange capacity (CEC) is the basis for soil fertilization and improvement, and thus an evaluation index of soil quality. Studies on the spatial heterogeneity of soil CEC can provide scientific basis for soil nutrient monitoring, management, and precision agriculture implementation. Spatial distribution of CEC in silt loam soil of Lycium barbarum in Zhongning was investigated based on the analysis of autocorrelation and interaction correlation. The CoCriging, ordinary least squares (OLS), geographically weighted regression Kriging (GWR) and Random Forest (RF) models were applied to perform regression analysis. After that, spatial interpolation mapping effect and the accuracy of the models were compared. The results showed that the average silt loam soil CEC in L. barbarum was 13.12 cmol·kg-1, belonging to moderately fertility. The distribution of soil CEC had spatial autocorrelation. There were different spatial relationships among CEC, pH, soil organic matter, clay and electrical conductivity in different lag distances. The prediction map of RF model avoided the large fragmentation and obvious mutations which occurred on both sides of the CEC map boundary in the prediction maps of CoKriging, OLS and GWR models. Consequently, soil CEC appeared as a natural and gentle transition in the spatial variation map. The RMSE of the RF model was 33.82%, 20.55% and 19.81% lower than that of CoKriging, OLS and GWR models, and R2 was increased by 8.84%, 51.92% and 7.69%, respectively. The RF model considered the location of sample space, and obviouslyimproved the accuracy of interpolation, making the mapping more smooth.
    Estimation and spatial distribution of carbon storage in urban greenspace.
    TANG Yu, SHI Tie-mao, BU Ying-jie, SHI Yu
    2020, 39(4):  1387-1398. 
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    Improving carbon (C) storage capacities of urban greenspace is of great significance to reduce atmospheric carbon dioxide (CO2) in urban areas and to mitigate the pressure of climate change. We established an estimation model with stepwise regression analysis on the aboveground carbon storage (AGC) of Shenyang urban greenspace within the thirdring road by field survey and remote sensing technology. Then, we examined the spatial distribution characteristics and put forward the strategies for improving AGC of urban greenspace. The total AGC of urban greenspace in Shenyang was 1.437 Tg, with a C density of 31.73 t·hm-2. The AGC in the eastern part of Shenyang was higher than that in the western part, which gradually decreased from the thirdring region to the city center. The AGC and C density of urban greenspace varied across different land use types. The residential land and regional traffic land had the highest and the lowest AGC, respectively (34.2×104 t, 2.57×104 t). The agricultural land and forest land had the highest C density (75.40 t·hm-2), while the residential land had the lowest (21.54 t·hm-2). Upgrading the vegetation coverage of the urban greenspace and increasing the DBH of trees can effectively improve carbon storage capacity. The upgrading of the lowcoverage areas in urban greenspace and the low and middlecoverage areas in residential greenspace can increase the AGC of urban greenspace by 7.21×104 t and 49.7×104 t, accounting for 5% and 34.6% of the total AGC in urban greenspace.