Table of Content

10 January 2020, Volume 39 Issue 1

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Changes of fractional vegetation coverage after returning farmland to forests and its response to climate in Shaanxi.

LI Deng-ke, WANG Zhao

2020, 39(1):  1-10. 

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Vegetation coverage of Shaanxi Province has been gradually increased since 1999 due to the implementation of largescale ecological construction and protection projects such as returning farmland to forest and grazing prohibition. To provide basis for ecological constructions and planning, we analyzed the spatiotemporal variations of vegetation coverage from 2000 to 2017 in Shaanxi using pixel dichotomy method and its response to climate change through spatial interpolation method, spatial correlation analysis and statistical methods based on MOD13Q1 data and meteorological data. The results showed that vegetation coverage in Shaanxi presented a fluctuational increase during 2000 to 2017 and peaked in 2012. The area with increased vegetation coverage and that with decreased coverage accounted for 82.4% and 17.6% of the total land area, respectively. The vegetation coverage in Northern Shaanxi increased obviously, while there was a decreasing trend in some areas when it reached the maximum value. The regions with large coefficient of variation of vegetation coverage mainly spread over the windblown and sandy areas, hilly and gully regions and surrounding cities along the Great Wall of Northern Shaanxi. There was no positive correlation between vegetation coverage and precipitation or air temperature in Shaanxi on an annual scale. The multiple correlation space between vegetation coverage and precipitation and temperature in the areas which accounted for 98.4% of the whole province failed to pass the 0.05 significance test. Our results indicated that ecological construction projects such as returning farmland to forest play an important role in promoting vegetation restoration and growth, and to a certain extent, reducing the sensitivity of vegetation growth to climatic factors. In the future, there will be a decreasing trend of the vegetation coverage in Shaanxi with the resources and environment constrains of ecological construction projects, and the expansion of urban land use. How to slow down such decreasing trend is an important issue for ecological construction and protection in Shaanxi Province.

Spatial and temporal dynamics and its driving factors of vegetation cover before and after the establishment of Poyang Lake Eco-economic Zone.

LIU Hai, ZHENG Liang, HUANG Yue-fei, WANG Min

2020, 39(1):  11-22. 

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Poyang Lake Eco-economic Zone is one of the accelerating poles of growth in central China. Understanding vegetation changes will provide support for more reasonable regulation and control of economic development and ecological protection in the Eco-economic Zone. Based on MODIS NDVI from 2000 to 2017, we explored the temporal and spatial characteristics of NDVI before and after the establishment of the Eco-economic Zone by using the slope of least square method and quantitatively examined the effects of climate and human factors on NDVI changes by means of correlation analysis. The results showed that before (2000-2008) and after (2009-2017) the establishment of the Zone, the overall vegetation showed an increasing growth trend. The NDVI growth showed a trend of 0.052 10 a^-1 (P<0.05) and 0.025 10 a^-1 (P<0.05) before and after the establishment of the Eco-economic Zone, respectively. After the establishment of the Eco-economic Zone, the growth of NDVI slowed down. Spatially, vegetation degradation occurred around prefectural cities and the provincial capital before the establishment of Eco-economic Zone, which intensified after its establishment. Furthermore, after the establishment of the Zone, vegetation degradation expanded to area around the lake, northern region and southern farming areas. In terms of influencing factors, on the regional scale, climatic factors were the dominant factors for NDVI change, with the influence of temperature on NDVI being greater than that of precipitation. In areas where NDVI changed significantly, human activities were the main factors affecting NDVI changes. Before the establishment of the Eco-economic Zone, the acceleration of urbanization was the main human factor causing the regional vegetation degradation. After the establishment of the Eco-economic Zone, vegetation degradation in the farming and lake areas, non-agricultural construction land occupation of other types of land, and rural homestead occupation of grassland were important anthropogenic factors inducing regional vegetation degradation.

The responses of gross primary production to drought in terrestrial ecosystems of China during 1980-2013.

DU Wen-li, SUN Shao-bo, WU Yun-tao, SONG Zhao-liang

2020, 39(1):  23-35. 

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Drought can substantially alter composition, structure and function of terrestrial ecosystems, and thus significantly affects terrestrial carbon cycle. Gross primary production (GPP), reflecting the productivity level of terrestrial ecosystems, is the largest component of the global terrestrial carbon fluxes. Here, we investigated the spatiotemporal patterns of GPP and drought in China during 1980-2013 and quantitatively analyzed the responses of GPP to drought at different temporal scales. Processbased model (DLM GPP) and eddy-covariance flux tower measurements (FLUXCOM GPP) were used to simulate GPP, while a drought index (standardized precipitation evapotranspiration index, SPEI) was employed to reflect the intensity of drought. The results showed that the two GPP estimates had similar spatio temporal patterns, characterized by increasing trends in southwest China but decreasing trends in most of areas in northeast China. Overall, there was a slight decrease in droughtimpacted areas in China, with most significant decrease in northwest inland. However, the south of Qinling Mountains-Huaihe River was becoming drier. The temporal variation of the two GPP estimates were generally consistent with SPEI, and displayed significant decreases in 1986, 1997, 2001 and 2011 due to severe drought events in these years. At the spatial scale, GPP estimates were correlated positively with SPEI in most regions of northern China, but they were negatively correlated in many areas of southern China. The effects of drought on GPP were more obvious in the semiarid regions. The responses of GPP to drought were closely related to temporal scales of drought index. There were differences in the drought response and sensitivity of GPP estimated by the two models. Therefore, to get a more accurate estimation of GPP, there is an urgent need to improve the current GPP models and establish more flux observation sites.

Species composition and diversity of plant community at different restoration stages of karst graben basin.

HA Wen-xiu, XIAO Gui-ying, CAO Jian-hua, LIU Yu-guo, CUI Ming, ZHOU Jin-xing

2020, 39(1):  36-45. 

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Understanding changes in species composition, community structure and biodiversity during natural vegetation restoration can provide important basis for the selection of tree species and the optimization of community structure in artificial vegetation restoration. In this study, different natural vegetations (herbosa, shrub and forest) in Jianshui County of Yunnan, a typical area of karst graben basin, were phytocoenologically investigated using the method of space substitutetime. Plant communities were stratified into tree, shrub, and herb layers at different restoration stages. The species composition, horizontal and vertical structure, and biodiversity of plant communities at different restoration stages were analyzed. The results showed that a total of 94 vascular plant species belonging to 43 families and 72 genera were recorded in 12 plots with a total area of 3200 m². Dominant species were mainly from Fagaceae,Rhamnaceae, Myrsinaceae, Rosaceae, and Oleaceae. During the herbosa shrubforest restoration, the number of families, genera, and species in community composition increased, the proportion of short and smallstature individuals decreased, but the whole community was still dominated by short and smallstature individuals. Richness and Shannon index of herbaceous plants were the highest in the early stage of vegetation restoration, i.e., the herbosa stage, while evenness was the highest in the shrub stage. Richness and Shannon index of woody species increased gradually with vegetation restoration, but evenness decreased gradually with vegetation restoration. With vegetation restoration, the ecological dominance of herbaceous layer and tree layer increased and that of shrub layer decreased. The herbaceous plants changed from the early annual or perennial herbs which were heliophilous, droughtresistant and tolerant of poor soil to the perennial herbs with strong resistance, and gradually changed to the neutral and sciophilous. Among them, Arundinella setosa could well adapt to the environment. The heliophilous tree species such as Rhamnus leptophylla,Myrsine africana,Carissa spinarum and Osteomeles anthyllidifolia were the pioneer species in this area. Their presence created conditions for other species, and they were gradually replaced by sciophilous species. These species could be used in the early stage of vegetation restoration. In the later stage of vegetation restoration, Quercus cocciferoides (Fagaceae) became a dominant species, which could be used in the shrub stage of vegetation restoration, or in the condition of artificial afforestation when conditions permitted. In the whole process of vegetation restoration, the predominance was shifting from short and small-stature species to tall and large-stature species, with increasing life span.

Differential vertical distribution of functional traits of fine roots of four cultivated tree species in the upper reaches of Minjiang River.

HU Hui, BAO Wei-kai, LI Fang-Lan

2020, 39(1):  46-56. 

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Functional traits of fine roots (≤2 mm in diameter) and their vertical distribution patterns reflect plant resource absorption strategy and determine belowground ecological processes in forests. A stratified excavation method was used to examine fineroot functional traits, vertical distribution and architecture of four cultivated trees (Cercidiphyllum japonicum, Betula platyphylla, Pinus armandii,andP. tabuliformis). The results showed that root length density, fine root biomass, specific root length (SRL) and specific root surface area (SRA) of broadleaf species were higher than those of coniferous species and that average diameter of fine root was smaller in broadleaf species. Root length density and fine root biomass of all the four species decreased significantly with increasing soil depth and concentrated in 0-20 cm soil layer. Moreover, trees grown in high elevation areas had higher root length density and fine root biomass than those in low elevation. There were no significant differences in SRL, SRA and fine root diameter among soil layers or elevations. There were significant differences of fine root architecture among species, with the highest first-order root number, tip density and bifurcation being found in Betula platyphylla, and the highest branching ratio inCercidiphyllum japonicum.However, fine-root architecture did not differ across the elevations. The SRL was positively correlated with the number of firstorder roots and tip density, the branching ratio was positively associated with root length density and fine root biomass, but all functional traits decreased with bifurcations. These results indicated that fine root architecture had significant effects on their vertical distribution and resource acquisition strategy.

Response of tree ring width in Cryptomeria japonica to climatic factors atdifferent elevations in Lushan Mountain.

BAI Tian-jun, DENG Wen-ping, KUANG Yuan-wen, LIU Yuan-qiu, YE Qing, NIU Jie-hui, WEN Lin-sheng, HUANG Rong

2020, 39(1):  57-66. 

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A total of 138 Cryptomeria japonica cores were collected at three different elevations in Lushan Nature Reserve. The relationship between radial growth and seasonal and monthly climate factors was analyzed by dendrography. Tree ring width of C. japonica at low elevation was more sensitive to changes of climatic factors than that at medium and high elevation. Radial growth was positively correlated with spring relative humidity at low elevation and middle elevation (P<0.05), negatively correlated with sunshine hours in spring and autumn mean temperature at low elevation (P<0.05), and negatively correlated with summer mean temperature and autumn mean temperature at middle elevation (P<0.05). There was a certain correlation between radial growth and climate factors in each season at high elevation, but the correlation was not significant. Radial growth was positively correlated with mean temperature of three different elevations in January (P<0.05) and negatively correlated with mean temperature in July of previous year and July of current year at low and middle elevation (P<0.05). High temperature would inhibit tree growth. Radial growth was negatively correlated with relative humidity, precipitation (P<0.05), positively correlated with sunshine hours (P<0.05) in April at low elevation, and decreased with the increase of elevation. The correlation between radial growth of C. japonica and main climatic factors in Lushan Mountain varied among different seasons. Radial growth was mainly influenced by the temperature in July and July of the previous year and the relative humidity in April. Elevation was an important factor affecting the response of radial growth to climatic factors. The standard annual ring width chronology established here was suitable for the study of tree ring climatology.

Changes of photosynthesis characteristics and chlorophyll fluorescence of Paranephelium hainanensis,a species withextremely small population. 

HONG Wen-jun, LUO Jin-huan, HE Shu-fen, MAI Zhi-tong, LIU Jun

2020, 39(1):  67-72. 

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To provide scientific basis for the protection and utilization of Paranephelium hainanensis, a species with extremely small population in Hainan Province, we explored its photosynthetic physiological characteristics. The seasonal and daily dynamics of photosynthesis characteristics and chlorophyll fluorescence parameters of adult trees and understory seedlings of P. hainanensis were measured by Li-COR portable photosynthetic apparatus and FC1000-H portable plant fluorescence imaging system. The daily variation of net photosynthetic rate (P_n) and transpiration rate (T_r) of both adult trees and seedlings showed an obvious “double peak” curve in July and November. The maximum P_n and T_r of adult trees were 9.24 mol·m^-2·s^-1 and 3.34 mol·m^-2·s^-1, respectively, resulting in a stronger photosynthetic capacity than that of understory seedlings. The mean value of maximum initial fluorescence (F₀) of adult trees was 323.04 and 135.87 in July and November, respectively. The average maximum fluorescence (F_m) of adult trees was 502.78 in July and 307.76 in November. Both F₀ and F_m of seedlings were lower than that of adult trees. TheF_v/F_m curve of adult trees showed a “singlevalley” pattern in July, and displayed a daily fluctuation with a trend of decline first, then rise and decline again in November. Results of correlation analysis showed that P_n of adult trees was positively correlated with T_r and F_v/F_m, and that P_n of seedlings was positively correlated with F₀ in July. In November, P_n of adult trees was positively correlated with T_r and F_m, and negatively correlated with F_v/F_m. The P_n of seedlings was significantly positively correlated with F_m. Our results suggest that P. hainanensis is a lightdemanding tree species, with specific photosynthetic characteristics and chlorophyll fluorescence parameters in July and November to adapt to environments. Water may be the key factor causing seasonal changes of photosynthetic rate and chlorophyll fluorescence parameters inP. hainanensis.  

Variation of flavonoid content in Taxus cuspidata seedlings and its responses to climate factors.

ZHANG Shi-hang, LIU Yan-hong

2020, 39(1):  73-81. 

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Plants form a defense system that responds to environmental change during evolutionary adaptation. Flavonoids, as vital secondary metabolites in plants, are important indicators of plant chemical defense capability in the defense system. In this study, seedlings ofTaxus cuspidatafrom five provenances were transplanted to four sites (37°N—43°N). The flavonoid content in leaf epidermis of T. cuspidata seedlings was determined by Multiplex-3 (Force-A, France) non-destructively. We analyzed the change patterns of flavonoid content in the leaf epidermis of T. cuspidata seedlings which was influenced by climate factors in the test sites and provenances. The relative contribution rate of environmental change in the test sites to the changes of flavonol index (FLAV) and anthocyanin index (ANTH) of T. cuspidata seedlings were higher than that of environmental change in the provenances and the interaction effect between the test sites and the provenances. The explanatory rates of climate factors in the test sites on FLAV and ANTH (49.8%, 55.4%) were higher than those of climatic factors in the provenances (35.3%, 29.2%). The FLAV and ANTH of T. cuspidataseedlings decreased with the increase of latitude in the test sites. The results of variation partitioning of climate factors in the test sites indicated that illumination had the highest explanation rate for the changes of FLAV and ANTH. The results of variation partitioning of climatic factors in the provenances revealed that waterrelated factors had the highest explanation rate for the change of FLAV and ANTH. The environmental change in the test sites played a leading role in driving the change of flavonoid content in T. cuspidataseedlings.T. cuspidata seedlings had stronger chemical defense ability in low latitude test sites. Illumination played a dominant role in driving the changes of flavonoid content in T. cuspidata seedlings in the short term, whereas water played a dominant role in the long term.

Responses of related products and key enzyme genes in sucrose metabolic pathway to high temperature in Jerusalem artichoke.

WEN Fen-liang, LONG Xiao-hua, YUE Yang, HE Teng-fei, GAO Xiu-mei, ZHOU Zhao-sheng

2020, 39(1):  82-92. 

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Sucrose is an important type of carbohydrates, the metabolism of which is closely related to plant growth, development and stress adaptation. Sucrose synthases (SUS), sucrose phosphate synthases (SPS) and sucrose invertases (INV) are three kinds of key enzymes involved in sucrose metabolism. Based on the transcriptome data, we identified 2 SUS, 2SPS and 7 INV genes (GenBank No: MK38694353) from Jerusalem artichoke, a bioenergy plant species. Bioinformatics analysis showed that SUS, SPS, and INV belonged to hydrophilic proteins, whose amino acid sequences had high similarity with other species. The three kinds of genes exhibited different expression patterns in the leaves of Jerusalem artichoke seedling treated at 25 ℃ and 30 ℃ for 10, 15, and 20 days, respectively. However, the product contents associated with sucrose metabolism, such as fructose, sucrose, and 1-kestose, had no significant changes, except for the total soluble sugar, the content of which was significantly reduced. This result indicated that these key enzyme genes responded to high temperature, and that sucrose metabolism was in a balanced state, reflecting that Jerusalem artichoke had a good tolerance ability to high temperature.

Effects of nitrogen fertilizer reduction on photosynthesis and nitrogen use efficiency in tea plant.

LI Wei, XIANG Fen, ZHOU Ling-yun, LIU Hong-yan, ZENG Ze-xuan

2020, 39(1):  93-98. 

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To examine the effects of nitrogen application level on the growth and nitrogen use efficiency of tea plant, we set four nitrogen fertilization treatments in the field: no nitrogen application (CK), applying pure nitrogen 16 kg·667 m^-2 (reducing nitrogen by 55.6%, treatment A), applying pure nitrogen 26 kg·667 m^-2(reducing nitrogen by 27.8%, treatment B) and applying pure nitrogen 36 kg·667 m^-2 (conventional fertilization, treatment CF). We examined the effects of different nitrogen application amounts on photosynthesis, yield, nitrogen absorption, and nitrogen use efficiency of tea plants. The results showed that treatment B promoted the chlorophyll content, net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r), but decreased the intercellular CO₂ concentration (C_i) and water use efficiency (WUE), compared to treatment CF. The yield of tea plant was the highest under treatment B, the agronomic efficiency of applied nitrogen fertilizer was the highest, the surplus of soil nutrients was less, and the efficiency of nitrogen utilization was high. The yield of tea plant was not significantly increased under treatment CF, the agronomic efficiency of applied nitrogen fertilizer was decreased, and there were more unutilized nutrients in soil. Therefore, compared with conventional fertilization, the yield of tea plant could be guaranteed and nitrogen use efficiency could be significantly improved under the condition of reducing nitrogen by 27.8%, which is beneficial to the sustainable development of tea industry.

Regulation of α-naphthaleneacetic acid on cold resistance of Brassica campestris seedlings under low temperature stress.

LUO Dan-yu, ZHANG Xiao-hua, LI Qiao-li, WANG Juan, ZHENG Sheng, ZHANG Teng-guo

2020, 39(1):  99-109. 

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We investigated the regulation of α-naphthaleneacetic acid (NAA) on cold resistance of Brassica campestris variety ‘Longyou 6’ seedlings by measuring parameters, including reactive oxygen (H₂O₂ and O₂^-_·) content, antioxidant enzyme activities, contents of malondialdehyde (MDA), soluble sugar, proline and chlorophyll, the expression level of antioxidant enzymes genes (APX, CAT, GR,SOD), RbohA-F, MAPK3/4/6, CBF and ICE1genes. Six treatments were applied to both leave and root tissues: 4 ℃, NAA+4 ℃, NAA+4 ℃+DPI (NADPH oxidase inhibitor), NAA+4 ℃+DMTU (H₂O₂ scavenger), NAA+4 ℃+U0126 (MAPK inhibitor), and NAA+4 ℃+Tungstate (NO production inhibitor). The results showed that cell viability, H₂O₂ and O₂^-_· contents, and MDA content in leaves decreased under NAA+4 ℃ treatment compared with 4 ℃ treatment. Antioxidant enzymes (CAT, SOD, APX and POD) in roots as well as soluble sugar, proline, chlorophyll contents and related genes expression in leaves increased. These results indicated thatBrassica campestris seedlings treated with α-naphthaleneacetic acid could significantly improve their antioxidant capacity, photosynthetic capacity, and the expression of related genes, and consequently enhance their cold resistance. Compared with NAA+4 ℃ treatment, chlorophyll content, antioxidant enzymes genes (APX, CAT, GR, SOD), RbohA-F,MAPK3/4/6, CBF andICE1 decreased in seedlings treated with NAA+4 ℃+inhibitors (DPI, DMTU, U0126 and Tungstate) to different extents, indicating that H₂O₂ and NO signaling molecules, NADPH oxidase and MAP kinase cascades are all involved in the regulation of αnaphthaleneacetic acid on cold resistance of Brassica campestris seedlings.

Growth and physiological responses of Scirpus mariqueter to extremely high temperatures.

LIU Xiao-tong, LI Xiu-zhen, YAN Zhong-zheng, XIE Zuo-lun, LIN Shi-wei

2020, 39(1):  110-119. 

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Extreme weather events are becoming more and more frequent in the context of global climate change, but we know little about the responses of salt marsh plants to extreme weather conditions. In this study, a 7-day controlled greenhouse experiment was conducted to investigate the response of growth, physiology and photosynthetic parameters of Scirpus mariqueter, a typical estuary salt marsh plant species, to extremely high temperatures (40, 45, 50 ℃). Results showed that high temperature (45-50 ℃) significantly enhanced the root to shoot ratio of S. mariqueter and that more biomass was allocated to underground to cope with the damage induced by the high temperature. The content of chlorophyll a, chlorophyll b and total chlorophyll decreased with the increases of temperature, indicating that high temperature inhibited the synthesis of chlorophylls. High temperature stress affected the physiology of S. mariqueter, malondialdehyde content in leaves and roots decreased significantly when exposed to high temperature (45-50 ℃), which indicates that S. mariqueter has a certain heat tolerance. The content of proline was significantly higher in high temperature treatment (40-50 ℃) than in control, soluble sugar content decreased significantly in leaves and increased in roots, suggesting that the osmotic adjustment substances produced by S. mariqueterwere active in resisting stress. Compared with that in control, net photosynthesis rate of S. mariqueter increased at 40 ℃, but decreased significantly at 45 and 50 ℃, accompanied by the decreases of stomatal conductivity, intercellular CO₂ concentration, transpiration rate, and water use efficiency, suggesting that photosynthesis rate of S. mariquetercan be promoted under a certain range of high temperature but be inhibited under extremely high temperature. Stomatal restriction was found to be the major limiting factor. Our results can provide a reference for understanding the adaptation mechanism of salt marsh plants to extremely high temperature in the context of climate change.

Seasonal variation in canopy conductance of urban green land and its environmental control.

BAI Yu-jie, ZHU Yuan-jun, MA Jing-yong, LIU Peng, YANG Rui-zhi, LI Cheng, ZHA Tian-shan

2020, 39(1):  120-129. 

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Canopy conductance (g_c) is a sensitive index indicating ecosystem response to environment. Understanding the response of canopy conductance to environmental factors is crucial for modelling ecosystem processes. We analyzed the seasonal dynamics of canopy conductance and its relationship with daily mean air temperature (T_a), photosynthetically active radiation (PAR), vapor pressure deficit (VPD) and soil water content (VWC) in Beijing Olympic Forest Park in the growing season from April to October 2012-2016 using eddy covariance technique. Regressions were used to test the effects of environmental factors on canopy conductance and the effects of canopy conductance on gross ecosystem productivity (GEP). The results showed that mean annual g_c was 3.97, 3.28, 2.13, 3.95 and 5.071 mm·s^-1 in 2012-2016, respectively, with a mean value of 3.69±1.99 mm·s^-1. The g_c started to increase in April and peaked in July orAugust, then gradually decreased at intraannual scale. VWC and T_a were the main factors affecting seasonal variation in g_c, which increased as increasing VWC and T_a. The effects of PAR and VPD on g_c varied yearly.GEP significantly increased with increasing g_c during the five years. Elevated soil water content and air temperature enhanced canopy conductance, and thus promoted GEP on a seasonal scale in urban green land.

Effects of reducing nitrogen combined with application of different types of organic fertilizers on  dry matter allocation, transport, and yield of maize.

LIU Bin-xiang, WANG Xing-long, ZHOU Fang, DU Lun-jing, JIN Rong, FENG Dong-ju, YUAN Ji-chao, KONG Fan-lei

2020, 39(1):  130-138. 

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To advocate for reduced use of chemical nitrogen fertilizers and explore scientific fertilization patterns and finally to achieve the planting goals of green, stable and high yield, an experiment with two factors of nitrogen reduction ratio and organic fertilizer application were conducted for two years, with blank treatment (CK₀) and routine nitrogen application rate (CK₁) as two controls. There were two levels of nitrogen reduction ratios, 20% (A₁) and 40% (A₂), and three levels of organic fertilizer, without organic fertilizer (B₀), common organic fertilizer (B₁), and bioorganic fertilizer (B₂). We examined the effects of nitrogen reduction with application of different organic fertilizers on the accumulation, allocation, and transport of dry matter and on the yield of maize. The results showed that the accumulation of dry matter and maize yield decreased with decreasing nitrogen application. Application of organic fertilizer significantly increased dry matter accumulation, allocation ratio in grain, contribution rate of dry matter to grains after silking, and yield. Treatments A₁B₁ and A₁B₂ increased dry matter accumulation in two years on average by 31.38% and 46.29%, and yield by 19.57%, 23.78%, respectively (P<0.05), compared with A₁B₀; and increased yield by 7.15% and 10.95%, respectively, compared with CK₁. Treatments A₂B₁ and A₂B₂ increased dry matter accumulation in two years on average by 19.68% and 35.13%, and yield by 6.33% and 7.48% (P<0.05), respectively, compared with A₂B₀; while decreased yield by 10.42% and 9.44%, respectively, compared with CK₁. Appropriate reduction of nitrogen fertilizer combined with application of organic fertilizer could improve dry matter accumulation, improve panicle traits, and ultimately increase yield of maize. In this study, application of 1500 kg·hm^-2 organic fertilizer with 20% reduction of chemical nitrogen fertilizer increased maize yield, which shows the best effect of bio-organic fertilizer application on the yield.

Morphology and leaf C, N and P stoichiometry of Pinus yunnanensis and their elevational variations.

LIU Jun-yan, DONG Ting-fa

2020, 39(1):  139-145. 

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Pinus yunnanensis, an endemic conifer species in southwestern China, is important for regional economic development and soil and water conservation. Here, we investigated the elevational variations of diameter at breast height (DBH), tree height, leaf morphology and carbon (C), nitrogen (N) and phosphorus (P) concentrations of mature individuals of P. yunnanensis in natural secondary forests of northeast Yunnan. We analyzed adaptive responses of foliar C∶N∶P stoichiometry along the elevation gradient. The results showed that DBH, tree height, leaf P concentration and C∶N ratio increased first and then decreased with elevation, while C∶P and N∶P ratios exhibited an opposite pattern. In addition, leaf length per bundle, specific leaf length, and concentrations of C and N were lower at higher elevation, while dry mass per bundle increased with elevation. Leaf N∶P (mean 5.82±0.10) in each elevation was lower than 14, which was significantly negatively correlated with DBH and tree height. These results suggest that P. yunnanensis showed adaptive growth and leaf nutrient balance with elevation. The growth of P. yunnanensis was limited by N, supporting the growth rate hypothesis where growth rate is expected to be negatively related with plant N∶P. The elevational patterns of stoichiometric characteristics of P. yunnanensis revealed in this study could be helpful for vegetation management.

Effects of two endophytic bacteria on mineral elements uptake of xanthoceras sorbifolia seedlings.

HAO Sha-sha, WU Yan, QIN Cai, WANG Ya-jing, HOU Zhi-xia, SU Shu-chai

2020, 39(1):  146-154. 

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We used Pseudomonas sp. XSB5 and Yorkella sp. GG10 as the test strains to explore the effects of endophytic bacteria with the ability of phosphorus solubilization and production of siderophore and IAA on nutrient uptake of Xanthoceras sorbifolia Bunge seedlings. The seeds of X. sorbifolia were immersed in the bacterial solution. After the first euphylla grew, X. sorbifolia seedlings were treated with the same amount of bacterial solution or water, and the growth of X. sorbifolia was analyzed four months later. The results showed that root and aerial part dry weights of X. sorbifolia were significantly increased after treated with XSB5 bacterial solution. After treated with GG10 bacterial solution, root and aerial part dry weights of X. sorbifolia were increased, and the root part dry weights increased significantly. The accumulation of nitrogen, phosphorus, and magnesium in X. sorbifolia was significantly enhanced, and the accumulation of iron varied with the treatment duration. The translocation factors of those four mineral elements were different depending on the treatment duration of different bacterial solutions. The available nitrogen and phosphorus contents in the culture substrate were significantly increased (except XSB530 treatment), and the available magnesium and iron contents were not significantly different compared to the control. Our results indicated that the inoculation of two endophytic bacteria could affect mineral elements in the culture substrate, increase the uptake of mineral elements by X. sorbifolia, change the transport capacity of mineral elements upwards, and promote the growth of X. sorbifolia. This study provides substaintial basis for the screening of the growthpromoting bacterial fertilizer.

Community characteristics of nematodes in agricultural soil of watermelon and melon with different cultivation years in Jiangsu Province.

GAO Fei, ZHAO He, ZHOU Feng, NI Wei, LI Hui-xin, JIAO Jia-guo, SUN Xing-xiang

2020, 39(1):  155-163. 

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This study aimed to explore the effects of cultivation years on the community structure of nematodes in agricultural soils of watermelon/melon. Soils from cropland planted with watermelon/melon for different cultivation years were collected in the main watermelon/melon production area of Jiangsu Province. We examined the populations, community structure and ecological index of soil nematodes. Results showed that 54 genera of soil nematodes were recorded, with an average abundance of 682 per 100 g dry soil. The dominant genera were Protorhabditis,Acrobeloides, andTylenchorhynchus. While nematode populations did not change with increasing cultivation years, the abundance of bacterivores and omnivorespredators significantly decreased and that of plant-parasites increased significantly. The populations of Tylenchorhynchus and Meloidogyne gradually increased. With increases of cultivation years, Shannon index (H), Wasilewska index (WI) and freeliving nematode maturity index (MI) decreased significantly, while the nematode channel ratio (NCR), plant parasitic index (PPI) and PPI/MI increased significantly. Results of correlation analysis showed that nematode populations were positively correlated with soil pH, available phosphorus, available zinc and available boron. The dominant genera of soil nematodes were largely affected by soil pH, organic matter, total nitrogen, available potassium, available boron and available zinc. The comprehensive analysis suggested that continuous planting of watermelon/melon can increase the abundance of plant-parasites in the soil, which may result in continuous cropping obstacle. Soils continuously planted with watermelon/melon for 6-10 years had a lowest diversity and a worst stability of nematodes, leading to soil deterioration.

Temporal and spatial variation of quantitative characteristics of arbuscular mycorrhizal fungi in Seriphidiumdominated desert grassland under different grazing intensities.

LI Na-na, LU Wei-hua, CHEN Yi-shi, SUN Hai-rong, JIN Sheng-fei, CHE Zhao-bi

2020, 39(1):  164-171. 

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We evaluated the response of rhizosphere AM fungi, root infection rate and seasonal dynamics to grazing. Three dominant plant species (Seriphidium transiliense, Stipa capillata, Festuca ovina, Carex liparocarpos) in theSeriphidiumdominated desert grassland were selected as the research materials. The results showed that the spore density and species richness of AM fungi and root colonization rate of plants decreased significantly with increasing grazing intensity (P<0.05), and diversity index decreased significantly under overgrazing (P<0.05). The spore density, species richness and root colonization rate in the 0-10 cm soil layer were significantly higher than those in the 10-20 cm and 20-30 cm soil layers (P<0.05) under the same grazing intensity. The diversity index showed no significant change with increasing soil depth (P>0.05). Meanwhile, different host plants had different dependence on AM fungi, and the colonization rate was in order of S. transiliense>F. ovina>C. liparocarpos. The spore density, species richness, root colonization rate of arbuscular mycorrhizal fungi had a seasonal variation. All three characters showed a “double peak” phenomenon, reaching the peak in June and September, which were almost synchronized with the growth rhythm of vegetation. Temperature had no significant effect on the spore density, richness and colonization rate of AM fungi, while rainfall had a significantly positive effect on the colonization rate (P<0.01).

Biomass of typical submerged macrophyte beds and shellfish communities in the Pearl River network in China.

ZENG Yan-yi, YANG Wan-ling, WANG Chao, PENG Song-yao, LI Yue-fei, LAI Zi-ni

2020, 39(1):  172-179. 

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The spatial-temporal variations of biomass of typical submerged macrophyte beds (SMBs) in four sampling sections (Zuotan, Xiaotang, Waihai, and Lanhe) of the Pearl River network were investigated in early December of 2015 and 2018. Meanwhile, the biomass variations of dominant shellfish species in sampling sections with SMBs and in adjacent areas without SMBs were investigated. The effects of hydrological, water quality, and sedimentary factors on the biomass of submerged macrophytes and dominant shellfish were analyzed by canonical correspondence analysis (CCA). The results showed that dominant species of typical SMBs in the Pearl River network was Vallisneria spinosa, which occasionally occurred with Ceratophyllum demersum, Myriophyllum spicatum, and Hydrilla verticillata. Both the species and biomass of SMBs in Zuotan, Waihai and Lanhe sections decreased during the two investigations except for Xiaotang section, where the biomass of SMB maintained a relatively stable level of up to 9 kg·m^-2 (wet weight). The biomass of shellfish in Xiaotang section was the highest, with an average value of 968.8 g·m^-2. The biomass of shellfish in the areas with SMBs was higher than that without SMBs. In the areas with SMBs, biomass of submerged macrophytes increased gradually with increasing water depth, whereas biomass of shellfish decreased. In the same sampling sections, biomass of shellfish in the areas without SMBs was significantly lower than that in the areas with SMBs, indicating that SMBs provided suitable habitats for the growth and reproduction of shellfish. The CCA results showed that changes in runoff and water level might be the main driving factors for the interannual succession of SMBs communities in the Pearl River network and that the maintenance of dominant species in SMBs may be regulated by the size fraction of sediment particle and water flow velocity.

Acclimation of Crested Ibis (Nipponia nippon) in Beidaihe wetland.

XIE Peng, ZHAO Hai-tong, Liu Dong-ping, ZHOU Liang, ZHAO Guo-li

2020, 39(1):  180-185. 

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Crested Ibis (Nipponia nippon) is one of the most endangered species in the world and a First-class National Protected Animal in China. To expand their distribution range, 20 Crested Ibises were introduced to the Beidaihe National Wetland Park in July 2018 from Yangxian Crested Ibis Breeding Center. To assess their adaptability to the simulated habitat of Beidaihe wetland, we investigated behaviors and habitat utilization of Crested Ibis in the acclimation cage from July to October 2018. During the acclimation, Crested Ibis quickly acquired flight skills to avoid collision with the net of the cage. The average flight duration increased from 106.8±93.4 s at the earlier stage to 145.8±118.1 s in the later stage. In the first day of the acclimation, 70% of the individuals nocturnally roosted on trees, while the rest on grassland or artificial roost bars. All Crested Ibis acquired the ability to roost on trees within 30 days of acclimation. Compared with the early stage, foraging time increased from 55.4% to 58.3%, and the percentage in the utilization of shallow water significantly increased in the later period. The alert time significantly increased in the later stage and showed a defensive response to predators such as raptors. After 87 days of acclimation, the behavior and habitat utilization of the individuals changed greatly and tended to be stable, indicating an adaptation to the new habitat. For the acclimation of the Crested Ibis, feeding method should be improved to increase the difficulty of foraging and feeding experiment of locally specific food should be conducted.

Nest site selection and niche differentiation of Eophona migratoria andDicrurus macrocercus in Yancheng coastal seawall forest.

LIU Bin, XU Peng, XUE Dan-dan, AN Yu-ting, LU Chang-hu

2020, 39(1):  186-193. 

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Nest site selection of birds during reproductive period is affected by many factors. Many kinds of passerines nest on the tree. Due to the lack of natural woodland in open coastal areas, the artificially planted seawall forests could provide essential nesting grounds for many passerine birds. In this study, nest distribution and nest site selection of two dominant breeding species (Eophona migratoria and Dicrurus macrocercus) were studied in seawall forest near Jiangsu Dafeng Milu National Nature Reserve from April to August 2018. A total of 127 nests belonging to 10 species were recorded, with the height of the most nests being above 5 m. The results of principal component analysis (PCA) showed that the main factors affecting nest site selection of E. migratoria were the traits of nested tree and shrub, and the secondary affecting factors were nest location, number of tree and safety (the cumulative contribution rate of the first five principal components was 71.9%). Similarly, traits of nest tree and shrub were the main factors affecting the nest selection of D. macrocercus, while nest direction and number of trees were the secondary factors (the cumulative contribution rate of the first five principal components was 78.0%). With the niche differentiation of nest sites, significant differences were detected in nest direction factor (U_test,Z=-3.013,P<0.01), nest height factor (U_test, Z=-6.718,P<0.01), nest location factor (U_test, Z=-5.402, P<0.01), and concealment factor (U_test,Z=-4.081, P<0.01). The niche overlap values of the two species were large (from 0.500 to 0.998) in most factors of nest site selection, indicating strong interspecific competition between them.

Habitat suitability assessment of shorebirds in Bohai Bay coast using MaxEnt Model.

ZHAO Ning, XIA Shao-xia, YU Xiu-bo, DUAN Hou-lang, LI Jin-pu, CHEN Ya-heng

2020, 39(1):  194-205. 

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Bohai Bay coast is one of the most important habitats for migratory shorebirds along the East AsiaAustralasian Flyway. However, the habitats are facing severe degradation and loss due to human activities. Assessing habitat suitability and identifying key areas are of great importance for the biodiversity conservation. We evaluated habitat suitability of Bohai Bay coasts in 2000 and 2015 with MaxEnt model based on the datasets including shorebirds occurrence data and environmental factors. The results showed that land use/cover, NDVI, mean annual temperature and aspect were the main factors affecting the distribution of shorebirds. Shorebirds mainly distributed at the coastal wetlands of southern Tangshan and Tianjin. From 2000 to 2015, the area of suitable habitats for shorebirds varied among different regions. The increments of suitable habitats were mainly located in southern Tianjin and southeastern Shandong, while the decrements were mainly located in Fengnan and Huanghua of Hebei, and Ninghe County of Tianjin. By identifying the distribution range of suitable habitats of shorebirds in the Bohai Bay, our results provide supports for shorebirds conservation and habitat management.

Effects of long-term reclamation on soil organic and inorganic carbon contents of aggregates in a saline wetland in Tianjin.

ZHU Yuan-shan, WANG Yi-dong, GUO Chang-cheng, SHANG Yun-tao, XUE Dong-mei, LI Jun, WANG Zhong-liang

2020, 39(1):  206-216. 

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The effects of reclamation on soil organic carbon (SOC) in marsh wetlands have been widely investigated, while research on coastal saline marshes is scarce, especially for soil inorganic carbon (SIC). Thus, it is difficult to comprehensively evaluate the impacts of reclamation on soil total carbon (TC). In this study, soil samples from 0-15 and 15-30 cm layers of Qilihai saline marsh wetland and the corresponding long-term reclaimed farmland (about 60 years) in Tianjin were collected and subsequently separated into four aggregate-size classes using wet sieving: >2, 0.25-2, 0.053-0.25 and <0.053 mm. After long-term reclamation, mass proportions of macroaggregates (>2 mm) decreased significantly (-48.1% and -58.1%) while microaggregates(0.053-0.25 mm) increased significantly (+166.1% and +70.0%) in the surface and subsurface soils, respectively. SOC contents decreased by 31.2%-56.8% in all aggregate sizes. The content of SIC in small macroaggregates (0.25-2 mm) and mineral fractions (<0.053 mm) increased significantly (+85.4% and +75.4%) in the surface soil. SIC contents increased significantly by 182.3%-448.2% in all aggregate sizes in the subsurface soil (15-30 cm). The TC content of large macroaggregates (>2 mm) and small macroaggregates (0.25-2 mm) reduced significantly in the surface soil (-12.9% and -21.9%), but TC contents of microaggregates (0.053-0.25 mm) and mineral particle fractions (<0.053 mm) in the surface soil and soil aggregates in the subsurface soil did not change. SIC contents demonstrated a significant compensation for the reduction of SOC contents following reclamation, which slows down or restrains TC loss in coastal salinized marsh wetlands. Therefore, the reclamation induced dynamics of SIC and its impact on total C should be paid more attention in future, especially in coastal saline areas.

Spatial distribution of soil nitrogen under the influence of drainage gully on alpine peatlands.

ZHU Yao-jun, MA Mu-yuan, GUO Jia, MAJI Cuo, ZHUOMA Jie

2020, 39(1):  217-223. 

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The spatial distribution characteristics of nitrogen in peatland soil around a drainage gully were analyzed to clarify the impacts of drainage gully on alpine peatland under the background of global change. The results would provide decision support for ecological restoration of degraded peatlands in Zoige plateau. A drainage gully was selected in the Zoige Wetland Nature Reserve as study area. Soil samples were collected on both sides of the drainage gully by ring knife. The contents of total nitrogen and alkalihydrolyzable nitrogen in the soil were measured. The results showed that soil total nitrogen content was 0.34-21.86 g·kg^-1, with an average of 11.26±6.22 g·kg^-1. Soil alkalihydrolyzable nitrogen content was 28.35-1965.60 mg·kg^-1, with an average of 889.53±470.31 mg·kg^-1. Soil nitrogen content was lower at higher altitudes and decreased along the direction of water flow in gully. The ratio of alkali-hydrolyzable nitrogen to total nitrogen was positively correlated with elevation. There were differences in nitrogen content between different distances in the direction perpendicular to the gully. The total nitrogen content was higher at sampling sites close to the gully, but with no statistical significance (P>0.05). The alkali-hydrolyzable nitrogen content on the left bank with lower elevation was smaller than that on the right bank. The alkali-hydrolyzable nitrogen in the surface soil near the ditch was the lowest (P<0.05). The ratio of alkali-hydrolyzable nitrogen to total nitrogen showed a “V” shape on both banks, decreasing first and then increasing with the distance from the gully. Both soil total nitrogen and alkali-hydrolyzable nitrogen were the highest in the surface layer and decreased with the soil depth. The distribution of soil nitrogen on the continuous block of terrace swamp decreased with the elevation. The surface soil nitrogen content was the highest, and the vertical change trend was inconsistent with the soil depth. Generally, drainage gully significantly reduced soil nitrogen content in the surface layer in the peatland. The impact of drainage gully on spatial distribution pattern of soil nitrogen in peatland varied with the distance from gully.

Correlation between ecosystem health conditions and land use in Dawen River basin.

SHEN Qi, WEI Jie, WU Wei, SHEN Chen-chen, WANG Tian-yi, WANG Li

2020, 39(1):  224-233. 

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To understand water ecological environment of Dawen River and the influence of land use type along the riparian zone, we conducted a survey on water ecology of Dawen River basin in April 2017. Principal component analysis and correlation analysis were used to screen and optimize a total of 19 candidate indicators in five aspects including watershed topography, hydrology, water environmental factors, major aquatic biological factors, and habitat quality. By analyzing weight coefficient of those indicators, a multiindicator assessment system for river ecosystem health in the Dawen River basin was constructed. The results showed that water environmental factors and aquatic organisms had a large weight in the health evaluation index system. The health status in the basin was dominated by general and poor grades, accounting for 58.33% and 20.83% of the total sampling points, respectively. The upper section of Yingwen River and southern tributaries of Dawen River, and the lower section of the main stream of the Dawen River were at excellent or good level. The area of urban village, industrial and mining land, farmland and traffic land were negatively correlated with water ecological health comprehensive index of Dawen River, which were the main factors responsible for the destruction of water ecosystems of the basin.

Removal of Cr(VI) from aqueous solution using nano δ-Bi₂O₃ loaded porous zeolite sphere fillers: Adsorption characteristics and influencing factors.

WANG Hong-sheng, WANG Sen, LI Yue, ZHANG Yu, YANG Jing-xuan, KONG Fan-long

2020, 39(1):  234-242. 

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Nanoδ-Bi₂O₃loaded porous zeolite sphere fillers (Bi-PZSF) were synthesized under hydrothermal conditions. Adsorption properties of Bi-PZSF for Cr(VI), including adsorption kinetics, equilibrium capacity and stability, were analyzed. The factors affecting the adsorption, such as dissolved oxygen, pH and competitive anions, and the adsorption mechanism was examined. The adsorption process was well described by the Langmuir model and the pseudosecondorder model. Dissolved oxygen had little effect on adsorption rate under neutral conditions. Adsorption capacity of Cr(VI) was 955.69 mg·kg^-1, which was nearly 120 times higher than that of natural zeolites. Bi-PZSF maintained excellent stability after adsorption and exhibited strong selective absorption of Cr(VI) in NO₃^-and SO₄^2- solutions. The removal rates of Cr(VI) were always above 97%. The removal of Cr(VI) by Bi-PZSF mainly depended on nanoδ-Bi₂O₃ adhering to the sphere, which was achieved by exchanging hydroxyl groups from the surface of δ-Bi₂O₃.

Effects of rhamnolipids with different structure ratios on the emulsification activity and oily sludge cleaning.

BAO Hong-xu, ZHANG Xin, ZHAO Feng, ZHAO Jin-yi, Li Guo-qiao, SHI Rong-jiu, HAN Si-qin, LI Ping, ZHANG Ying

2020, 39(1):  243-251. 

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Physicochemical activities and oily sludge cleaning effect of rhamnolipids with different structure compositions were examined using crude oil and oily sludge of Daqing Oilfield. Meanwhile, the parameters of oily sludge cleaning were optimized. Results showed that there was a positive relationship between the proportion of monorhamnolipids and surface activity of rhamnolipids. The proportion of di-rhamnolipids was positively correlated with emulsifying ability of rhamnolipids to crude oil. Different ratios of mono-rhamnolipids and di-rhamnolipids affected oily sludge cleaning effect. The cleaning efficiency was the highest at a ratio of 50:50. The optimized cleaning parameters were as follows: rhamnolipids concentration of 1.0 g·L^-1, hot wash time of 1.5 h, hot wash temperature of 65 ℃, eluting power of 220 r·min^-1, and solid liquid ratio of 1:5. The cleaning efficiency was up to 81.3% under optimized conditions. After cleaning process, oil content of the ground oily sludge was reduced from 29.6% to 5.5%. The oil recovery efficiency was 87.3%. The washed crude oil has no obvious emulsification and is easy to separate. Different ratios of mono-rhamnolipids and di-rhamnolipids affect their physicochemical properties and the oily sludge cleaning effect.

Responses of growth and physiology of rice (Oryza sativa L.) seedling roots to MWCNTs-COOH combined with Cd stress.

LIU Ling, DAI Hui-fang, TANG Feng-xue, ZHANG Jin, XU Ting-ting, LIU Hai-yan

2020, 39(1):  252-259. 

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To investigate the effects of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) combined with cadmium (Cd) stress on plant growth and physiology, we measured the changes of root growth, oxidative damage, activity of antioxidant enzymes, and contents of cadmium in roots of rice (Oryza sativa L.) seedlings treated with MWCNTs-COOH (0-12.0mg·L^-1) and Cd (10 μmol·L^-1) for three weeks. The results showed that: (1) Root length and fresh weight in MWCNTs-COOH treatment were lower than those of the control, and they increased first and then decreased over time. When the concentration of MWCNTs-COOH reached 12.0 mg·L^-1, root length and fresh weight were lower than those of the control, with a reduction of 9.3% and 15.2%, respectively. (2) Root length, fresh weight and dry weight of rice seedlings treated with the combination of MWCNTs-COOH and Cd were lower than those of the MWCNTs-COOH treatment alone. Under MWCNTs-COOH stress, superoxide radicals (O₂^-_·) accumulated significantly, and superoxide dismutase (SOD) and peroxidase (POD) activities of rice increased. SOD and POD activities were the highest under 3.0 and 6.0 mg·L^-1 MWCNTs-COOH treatments; (3) SOD and POD activities of rice roots under MWCNTs-COOH combined Cd stress were lower, while malondialdehyde (MDA) and carbonylation protein contents were significantly higher than those under Cd stress alone. (4) When rice was treated with combination of MWCNTs-COOH and Cd, the death of root tip cells accelerated. Most of the root cap cells treated with 10 μmol·L^-1 Cd+12.0 mg·L^-1 MWCNTs-COOH were stained with Evans Blue. (5) After treated with 1.5-6.0 mg·L^-1 MWCNTs-COOH and Cd, the cadmium contents in the roots of rice seedlings showed an increasing trend, and reached a maximum of 303.30 μg·g^-1 at the concentration of 6.0 mg·L^-1. Our results indicated that high concentrations of MWCNTs-COOH and its combination with Cd are toxic to rice roots.

Isolation of high molecular weight PAHs degrading bacteria and its application in the electro-bioremediation of contaminated soil.

ZHANG Jin-bao, LI Feng-mei, GUO Shu-hai, LU Wen-jie, SUN Zi-cheng, ZHAO Ming-yang

2020, 39(1):  260-269. 

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Nine high molecular weight (HMW) PAH degrading bacteria were isolated from PAH contaminated soil of a coking plant site using the enrichment procedure and detection of polycyclic aromatic hydrocarbon dioxygenase gene. The degradation ability of HMW-PAHs was examined in flasks with pyrene as carbon source. The results showed that strains J6, S5, S4, S2 and B4 had stronger degradation ability for pyrene. After 21 days, the degradation rates of pyrene in all treatments were higher than 55%. The degradation rate of pyrene in B4 treatment was the highest, reaching 70.2%. We further analyzed the degradation ability of five strains and their mixture in pyrenecontaminated soil. Results showed that the degradation rate of pyrene in the treatment inoculating mixed bacteria were higher than that inoculating single bacterium. Among them, the treatments H4 (mixture) and B4 had better degradation rate of pyrene, and the degradation rates of pyrene reached 29.3% and 18.3% after 49 d, respectively. J6, S5, S4, S2 and B4 were identified as Rhodococcus ruber, Bacillus sp.,Sphingopyxissp., Sphingopyxissp. and Pseudomonas sp. respectively based on sequence analysis of 16S rRNA. The abundance and activity of microorganisms in the H4 and B4 treatments under electric field conditions were significantly increased, and the degradation rates of pyrene were 32.9% and 20.1% higher than those without electric field conditions. This indicated that  five strains of HMW-PAH degrading bacteria had strong electric field adaptability and could be applied in the electro bioremediation of HMW-PAHs contaminated soil.

Research progress on input of plant community-derived soil organic carbon and its responses to climate warming.

MA Zhi-liang, ZHAO Wen-qiang

2020, 39(1):  270-281. 

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Plant communities, as one of the main source of soil organic carbon, can transport organic carbon into soils through litter decomposition, fine root turnover, and root exudation. Global climate warming is profoundly changing the distribution, structure and function of plant communities, with consequences on the amount and quality of plant communityderived soil organic carbon inputs through changing aboveand below ground litter production and decomposition and root exudation processes. In this review, we systematically summarized research progress on soil organic carbon inputs by plant communities and its responses to climate warming. Climate warming could directly affect litter production and root exudation processes by changing plant growth, and indirectly affect carbon inputs by changing the biotic and abiotic factors affecting litter decomposition, such as microenvironmental condition, litter quality and structure and activity of decomposers. Climate warming could indirectly affect carbon inputs from plant roots by affecting root traits and root exudate composition. However, the potential mechanisms need to be further explored. Future studies should focus on the mechanisms underlying the effects of climate warming on plant community structure, which could affect soil organic carbon inputs and the contribution of coarse woody debris to soil organic carbon. The integration of litter decomposition and root exudation processes should be conducted to better understand the contribution of plant communities to soil carbon pool and carbon cycling processes under climate warming.

Research advances of invasive alien plant Amaranthus retroflexus L.

WEI Ying, LI Qian, LI Yang, MAO Zhu-xin, WANG Yu-chao, YUE Ming

2020, 39(1):  282-291. 

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We reviewed research progress on the biological characteristics, invasion and expansion history, possible distribution area, environmental limiting factors, control methods and application ofAmaranthus retroflexusL. The results showed that A. retroflexus could adapt to a wide range of germination conditions, especially at high temperature. A. retroflexus can adjust its biomass allocation and physiological and biochemical processes to cope with environmental change. This species has strong phenotypic plasticity. Under global climate change, its invasion is continuing and it will expand to southwest China. Developing and screening new herbicides and exploring the application methods are the solutions to reply the resistance to drugs of A. retroflexus.A. retroflexus has high nutritional and medicinal value, as well as potential use in phytoremediation. Current research on this species is still insufficient; following issues should be strengthened: (1) adaptive evolutionary mechanism under environmental pressure and molecular basis of rapid adaptation; (2) its effect on soil microbial community, plant community structure and animals in the invaded area and the underlying mechanism; (3) balancing between the application and prevention of A. retroflexus invasion.

Demand, achievement and issues of fish passage facilities in China.

CAI Lu, ZHANG Peng, HOU Yi-qun, JIN Yao, YAO Jun, HUANG Ying-ping

2020, 39(1):  292-299. 

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We summarized the effects of water resources and hydropower engineering on river connectivity and the strategies in construction of fish passage facilities. We further analyzed demands for facilities construction in China from the aspects of river fragmentation and fish migration, and introduced the achievements of facilities construction in China. We had recommendations on six issues of fish passage facilities: (1) Scientifically select target fish species using quantitative and multifactorial methods. (2) Conduct experiments on fish swimming behaviors under more natural conditions, using large swim channels and more complex flow patterns. (3) Invest in large fishways with high flows (>1% river flow) to attract and pass more fish. (4) Build facilities that could assist downstream passage of fish and allow fish to pass low head hydraulic structures. (5) Expand data collection by increasing the number of monitoring sites and the duration and frequency of monitoring. (6) Work cooperatively on fish habitat restoration, breed/release programs, ecological operation of dams, and stratified water intakes to improve fish passage facilities and fish stocks.

Overview of fire management in the Wildland-Urban Interface of the United States and its enlightenment to China.

ZHENG Wen-xia, GUO Xin-bin, GUO Lin-fei, MA Yuan-fan, GUO Fu-tao

2020, 39(1):  300-307. 

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With the growth of global population, the expansions of Wildland-Urban Interfaces (WUIs) are accelerating worldwide. In the United States, WUIs are widely distributed with large population. They are highly vulnerable to wildfire due to its direct connection with the forests. The human life and property in the WUIs is facing a great threat. With a long history of management practice, the United States has formed a relatively complete management system on wildfire prevention and suppression in WUIs. We summarized the management system of wildfire in WUIs of the United States from the aspects of formation of WUIs, wildfire situation, and the measures of wildfire prevention and suppression. In addition, current situation and problems of wildfire management in WUIs of China were analyzed. Based on the experience from the United States, we proposed suggestions for improving the fire management of WUIs in China: (1) developing fire management plan for the WUIs; (2) rationally utilizing the prescribed burning; (3) developing early fire warning system; (4) improving the capability of wildfire prevention in WUI community; (5) improving the fire fighting level of firefighters; (6) promoting fire fighting strategy in WUIs.

Plant phenotypic measurement of Solidago canadensis using Terrestrial LiDAR Scanning.

ZHOU Zhi-yu, CHEN Bin, ZHENG Guang, WU Bing-xiao, MIAO Xin-yu, YANG Dan, XU Chi

2020, 39(1):  308-314. 

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Plant phenotype as a function of the interactions between its genotype and environment reflects plant adaptive strategies in the environment. Precise measurements of plant phenotypic traits are the basis for accurate determination of plant morphology, structure, growth and development. In this study, 20 individuals of Solidago canadensis were cultivated for three months, and they were scanned in situonce a month at nine different scanning stations using Terrestrial LiDAR Scanning (TLS) system, which presented a repeated measurement of three-dimensional point cloud data during plant growth. Plant height was obtained by constructing normal vectors with threedimensional coordinates of multiple endpoints. The leaves were reconstructed by threedimensional point cloud data. Based on the Delaunay triangulation method, leaf point cloud was encapsulated to pursue the data of leaf area, leaf inclination angle and azimuth angle. In addition, we measured these traits with traditionally hand-based (THB) methods, i.e. using ruler for plant height, leaf area meter for leaf area, and compass and protractor for leaf inclination angle and leaf azimuthal angle. By comparing the results obtained with TLS and THB methods, we found that the similarity in trait values for plant height, leaf area, leaf inclination angle and leaf azimuthal angle were 0.991, 0.989, 0.949 and 0.871, respectively. Therefore, our results suggest that the LiDAR scanning method can provide accurate and multi-type phenotypic traits of plants in a fast scanning event. As a non-destructive method, it is suitable for long-term repeated observations of plant phenotypic traits.

Comparative analysis of sensible heat flux observed by large aperture scintillometer and eddy-covariance system in Nanjing.

WANG Liang, HU Ning, WANG Yong-wei, WANG Lu-yao, ZHAO Xiang, LIU Shou-dong

2020, 39(1):  315-325. 

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Turbulence is one of the key processes for energy exchange between land surface and atmosphere. Accurate observation on turbulent fluxes has been an important issue in the researches on urban boundary layer. Based on simultaneous observation of a large aperture scintillometer (LAS) and an eddy covariance system (EC) installed in the campus of Nanjing University of Information Science and Technology, we compared sensible heat flux measured by those two systems. The effects of underlying surface heterogeneity on the sensible heat flux were analyzed combined with the normalized vegetation index (NDVI) and the normalized building index (NDBI). The results showed that LAS and EC had a good correlation (R²=0.76), with a regression slope of 0.95. During the daytime, sensible heat flux obtained from LAS was larger than that by EC, and their difference varied between 18.8 and 39.4 W·m^-2. At night, both of them fluctuated around zero, and the difference varied between 4.8 and 28.7 W·m^-2. On the monthly scale, the difference between LAS and EC was the largest in August, followed by July and April, and the least in June. The difference attributed to the different footprints caused by the changes of wind direction. NDVI in the footprint was negatively correlated with sensible heat flux to net radiation (k=-0.34, P<0.05). NDBI in the footprint was significantly positively correlated with ratio of sensible heat flux to net radiation (k=1.15, P<0.05).

Ecological security evaluation and prediction based on ARIMA-ANN model: A case study of Hexi Corridor urban agglomeration.

WANG Yi, WEI Jiang-chao, SUN Qi-yuan, WANG Fei-feng

2020, 39(1):  326-336. 

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Ecological security is the prerequisite for sustainable development of society and economy. It is of great significance to study the historical evolution and development trend of regional ecological security. An ecological security evaluation index system was established based on PSREES model. The comprehensive index method was adopted to calculate the ecological security values of five cities in the Hexi Corridor urban agglomeration from 2008 to 2017. ARIMA-ANN composite model was used to predict the future trend of regional ecological security. The ecological security in Hexi Corridor showed a fluctuating and rising state. The evolution characteristics were consistent with the regional ecological protection planning and policy. The ecological security level of each city was different from the ideal state. The security value of pressure layer in Zhangye, Jingchan and Jiuquan were relatively low, with some potential ecological risk. The ecological security trends in the Hexi Corridor urban agglomeration were predicted using ARIMA model and ARIMA-ANN model, with the results showing the average relative error and correlation coefficient of 2.01%, 0.8852 (ARIMA), and 1.09%, 0.9665 (ARIMA-ANN). Moreover, the ARIMA-ANN composite model predicted that ecological security value of Hexi Corridor would reach 0.8107 (level V) in 2020. This study verified the high accuracy and precision of ARIMA-ANN composite model for evaluating regional ecological security evolution and predicting development trend. It is of vital practical value for the optimization of regional ecological spatial layout and security management.

Aboveground biomass modeling and allometric growth characteristics of Artemisia capillaris Thunb. under different water availabilities.

LI Lang, LI Yi-bo, MA Quan-hui, YU Hong-ying, LIU Xiao-di, QI Miao, XU Zhen-zhu

2020, 39(1):  337-348. 

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Establishing plant biomass models to explore plant allocation strategy and allometric growth relationships under various environments is of importance for better understanding plant community structure and function, and the storage and allocation mechanism of carbon. An in situ field experiment was conducted to examine the effects of water availability on plant biomass and allocation strategy in a desert steppe in northern China. Several key but easily measured parameters of a common species, Artemisia capillaris Thunb., in the desert steppe, including height, basal diameter, number of branches, crown, and biomass under different precipitation levels were used to construct plant biomass models. The allometric growth relationship of A. capillaris was analyzed using a standardized major axis regression. The results showed that the optimal parameters for biomass models along the gradient of water availability changed a lot. The allometric growth relationships within plant organs and that between plant organ and aboveground biomass were quite discrepant, with isometric growth relationships under extremely increased and decreased 50% precipitation amounts relative to the ambient. It indicated that there was a tradeoff of carbon allocation between plant organs under different water conditions, in accordance with the hypothesis of the best optimal resource allocation. However, the allocation competition may attenuate under extreme climatic conditions. The findings suggest that it is necessary to incorporate environmental factors such as precipitation for conducting biomass models of herbs in desert steppe. Our results can provide methodological support and theoretical basis for constructing biomass assessing models and understanding the adaptation of allometric growth to environment for herbs in arid ecosystems.