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Table of Content

    10 April 2019, Volume 38 Issue 4
    Effects of short-term warming and nitrogen addition on CO2 emission during growing season in an alpine swamp meadow ecosystem of Qinghai-Tibetan Plateau.
    BAI Wei, XI Jing-yang, WANG Gen-xu
    2019, 38(4):  927-936. 
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    To investigate the interactive effects of global warming and increased nitrogen deposition on ecosystem respiration, a short-term experiment was carried out during growth season in an alpine swamp meadow of Qinghai-Tibetan Plateau, using open top champers (OTC) and nitrogen addition to simulate warming and nitrogen deposition, respectively. Warming, nitrogen addition, and their interaction significantly increased ecosystem respiration rate by affecting plant biomass, soil microbial quantity and activity, and soil nutrient status. The correlations between ecosystem respiration and each of the environmental factors were exponential or quadric multinomial, with the significance levels of such regressions declining with the increases of complexity of treatments. As soil water availability is sufficient in swamp meadow, air temperature and soil temperature at the depth of 5 cm could explain 80% of the variations of ecosystem respiration. Warming significantly increased above and below-ground biomass, and enhanced the proportions of below-ground biomass. Nitrogen addition significantly increased above-ground biomass and had no effect on below-ground biomass. Under warming condition, nitrogen addition significantly increased above and below-ground biomass, but with no impacts on biomass allocation.
    Spatial structure of standing dead trees in Pinus tabuliformis mixed forest in western Beijing.
    ZHANG Lian-jin, WANG Tian-gang, FENG Huan-ying, DU Man-yi, LAI Guang-hui, XIN Xue-bing, KONG Qing-yun
    2019, 38(4):  937-944. 
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    Standing dead trees are an important component of forest ecosystems, with a critical role in the stability and development of forest ecosystems. Based on survey data of a 1.08 hm2 plot inPinus tabuliformis mixed forest in western Beijing, the spatial structure of standing dead trees was analyzed, including tree species composition, diameter structure, height structure, univariate and bivariate distribution of spatial structure parameters. There were 191 standing dead trees, with a density of about 177 stems·hm-2. Pinaceae, which accounted for 64% of standing dead trees, was the dominant family. Larix principis rupprechtiiis the dominant species. The diameter distribution was an inverted “J” type, dominated by small trees with diameter less than 11 cm. The tree height distribution presented as unimodal with a narrow range. L. principisrupprechtii, Syringa pekinensis and P. tabuliformis distributed in most diameter and height classes. The standing dead trees were generally in a state of random distribution with significant size differentiation and low mingling, and they were mostly surrounded by living trees. The structural characteristics of L. principis rupprechtii, P. tabuliformis, S. pekinensis and Armeniaca sibiricawere roughly similar to the overall pattern. Most standing dead trees, which were surrounded by the same species or only one other species, were in a state of low mingling and disadvantage. About half of standing dead trees showed a random distribution, and most of them were at a disadvantage status and their surroundings were mostly living trees of the same species. There were different frequencies of standing dead trees with different dominance, but the number of non-dominant trees was higher than that of dominant trees. The spatial structure of standing dead trees in P. tabuliformis mixed forest reflected that intraspecific competition under density restriction was the main reason for the formation of standing dead trees. Our results would provide scientific basis for the protection and sustainable management of coniferous-broadleaved mixed forest.
    Effects of gold nanoparticles on seed germination and seedling growth of mung bean (Phaseolus radiatus) and the underlying physiological mechanism.
    SHI Xia-ming, GAO Chao, QIAO Ning-ning, WANG Jing-jing, ZHU Jin-miao, CHEN Yan-song, CAI Xu-ran, XU De-cong, WANG Meng-jun, XU Zhong-dong
    2019, 38(4):  945-952. 
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    The phytotoxicical effects of gold nanoparticles on Phaseolus radiatus and the underlying physiological mechanism were examined in a seed germination and seedling cultivation experiment. The results showed that gold nanoparticles inhibited seed germination and seedling growth of P. radiatus. Seed germination characteristics (including seed germination potential, germination rate, germination index, and vigor index) and seedling growth indices (including seedling height, root length, and fresh weight) significantly decreased with the increasing concentration of gold nanoparticles. The decrease in root length and root fresh weight was more significant than that in seedling height and shoot fresh weight. An increased mortality rate of seedlings was associated with an elevated concentration of gold nanoparticles. The physiological characteristics of P. radiatusseedlings were significantly affected by gold nanoparticles. With the increasing concentration of gold nanoparticles, chlorophyll and nitrogen contents in leaves decreased, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in both shoot and root increased first and then decreased, and malondialdehyde (MDA) contents increased. The activities of those three anti-oxygen enzymes in shoot were higher than those in root, while the MDA content in shoot was lower than that in root. In conclusion, the phytotoxicity of gold nanoparticles was stronger in root tissues than in shoot issues, and this effect was concentration-dependent. Decreased chlorophyll and nitrogen contents in leaves and altered oxidative stress levels contributed to the morphological changes of seedlings. Our findings provide an important insight for the safe application and potential ecological risk assessment of gold nanoparticles.  
    Effects of utilization regimes on spatial heterogeneity of the  dominant species Cleistogenes squarrosa in Stipa grandissteppe.
    ZHANG Feng, YANG Yang, QIAO Ji-Rong, JIA Li-Xin, ZHAO Tian-Qi, ZHAO Meng-Li
    2019, 38(4):  953-960. 
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    A field experiment was carried out to evaluate the changes of spatial distribution of Cleistogenes squarrosa population on Stipagrandis steppe under different utilization regimes (exclosure, mowing, and grazing) in Maodeng ranch, Xilingol, Inner Mongolia. With geostatistics, the semivariance function, fractal dimension and Kriging interpolation method, we analyzed the effects of small-scale spatial heterogeneity of C. squarrosa population in exclosure, grazing, and mowing treatments. The results showed that population density of C. squarrosa followed the order: grazing (28.63 plants·m-2) > exclosure (13.60 plants·m-2) > mowing (3.85 plants·m-2) (P<0.05). Grazing increased while mowing reduced population density of C. squarrosa (both P<0.05). Population densities of C. squarrosa under the treatments of exclosure, grazing and mowing were consistent with exponential model, spherical model and spherical model, respectively. According to the results of spatial distribution pattern analysis, the structural ratio ofC. squarrosa population under mowing, grazing and exclosure was 91.9%, 75.3%, and 71.1%, respectively. The spatial autocorrelations of grazing and mowing treatments were higher mainly due to structural factors, while that of the exclosure treatment was moderate and affected by random factors. Combined with the fractal dimension and 2D and 3D views, the spatial structure of the three plots was good with simple spatial distribution, indicating that reasonable grazing and mowing did not impact the distribution of C. squarrosa population. Compared to the exclosure treatment, grazing increased and mowing reduced the spatial heterogeneity of C. squarrosa population.
    Flavonoid components and their relationship with flower colors in five species of CamelliasectionChrysantha.
    LI Xin-lei, WANG Jia-tong, SUN Zhen-yuan, WANG Jie, YIN Heng-fu, FAN Zheng-qi, LI Ji-yuan, JIANG Chang-jie, HUANG Xiao-na
    2019, 38(4):  961-966. 
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    The flower colors, flavonoid components and contents in five species of Camellia section Chrysantha, including Camellia nitidissima, C. microcarpa,C. achrysantha, C. longruiensis and C. longzhouensis, were measured. The flower colors were measured by CIE L*a*b*scale, and flavonoid components and contents were measured by ultra-performance liquid chromatography quadrupoletime offlight mass spectrometry. The relationship between flower colors and flavonoid components was explored by multiple linear regression analyses. Eight flavonoids weredetected in the five species. The flavonoids including pelargonium-3-O-glucoside (Pg3G), luteolin-7-O-rutinoside (Lu7R), narirutin and erodcyol were identified in the five speciesfor the first time. The quercetin-3-O-glucoside (Qu3G), quercetin-7-O-glucoside (Qu7G), quercetin-3-O-rutinoside (Qu3R) and kaempferol-3-O-glucoside (Km3G) were identified in C. microcarpa and C. achrysantha for the first time. Among the five species, the total flavonoid content of C. nitidissima was the highest, followed by C. achrysantha and C. microcarpa, and that of C. longruiensisand C. longzhouensiswere lower. Qu3G, Qu3R and Pg3G were the main flavonoid components in C. nitidissima and C. microcarpa. Qu3G and Qu7G were the main flavonoid components in C. achrysantha. Erodcyol and narirutin were the main flavonoid components in C. longruiensisand C. longzhouensis. We conclude that Qu3G and Qu3R were the important pigments determining the yellow coloring of petals of Camellia section Chrysantha. Erodcyol had a significantly positive correlation with red coloring of petals. Pg3G affected the brilliance of flower colors.
    Fine root adaptation strategy of moso bamboo during its expansion into Chinese fir forest.
    CAI Chun-ju, FAN Shao-hui, LIU Xi-zhen, LIU Guang-lu
    2019, 38(4):  967-972. 
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    Fine roots are important for the function of individual plants. To better reveal the fine root strategy of bamboo expansion, we explored its plasticity in the process of Phyllostachys edulis expanding into Chinese fir forest. We compared the functional traits of fine roots of moso bamboo in different stages and explored the morphological plasticity when it expanded into Chinese fir forest. The fine root biomass (FRB), root length density (RLD), specific root length (SRL), key nutrient contents and their ratios were measured. The results showed that the FRB and RLD increased with moso bamboo expansion. The SRL and the content of N and P decreased with moso bamboo expansion. The FRB and RLD at final expansion stage were 7.03 times and 1.57 times of that at the initial expansion stage. The FRB and RLD at final expansion stage were 1683.04±188.17 g·m2 and 6483.14±846.82 m·m-3, respectively. The SRL decreased from 2.61±0.20 m·g-1 at initial expansion stage to 0.70±0.06 m·g-1 at the final expansion stage, with the former being 3.73 times that of latter. The N content decreased by 41.11%, from 5.06 g·kg-1 at initial expansion stage to 2.98 g·kg-1 at the final expansion stage. The P content decreased by 43.33%, from 0.30 g·kg-1 at initial expansion stage to 0.17 g·kg-1 at final expansion stage. There were significant correlations between N, P, K contents, C∶N and the FRB and SRL, indicating that the morphological traits and nutrient contents of fine roots varied with environmental changes and that the fine roots of moso bamboo had higher plasticity. The moso bamboo can grow quickly and use soil resources efficiently in new environment by increasing the SRL and N and P contents.
    The responses of carbon and nitrogen pool composition to plant diversity in typical grasslands of Henan Province.
    ZHAO Wei, LI Lin, WANG Yan-jie
    2019, 38(4):  973-982. 
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    With field investigation and laboratory analysis, the relationships of plant diversity with carbon and nitrogen pool composition in four typical grassland ecosystems including warmtemperate tussock (WT), warmtemperate shrub tussock (WS), tropical tussock (TT) and tropical shrub tussock (TS) in Henan Province were explored through redundancy analysis (RDA). The results showed that plant species diversity in the shrub tussocks was higher than that of the tussocks. The plant functional groups in Henan grasslands were conformed to the regional characteristics. The proportion of C3 plants was much higher than that of C4 plants, while the weeds accounted for 64%-73%. The proportion of plant species with sexual and asexual reproduction patterns was up to 49%-56%. The composition of life forms was complex. Warm grassland was dominated by perennial herbs and shrubs, and tropical grassland was dominated by annual orbiennial herbs and perennial herbs. The results of RDA analysis showed that nitrogen density in the vegetation of WT and WS was positively correlated with Shannon and Pielou indices. Community carbon density was negatively correlated with soil nitrogen density and Shannon and Pielou indices. There was a positive correlation between carbon and nitrogen density and species richness of TT, a positive correlation between soil nitrogen density and Shannon and Pielou indices, and a negative correlation between vegetation nitrogen density and Shannon and Pielou indices. Soil carbon and nitrogen density of TS was positively correlated with Shannon index, and community carbon and nitrogen density was negatively correlated with species richness and Shannon index. That is, species diversity and vegetation composition of different grassland types co-affected carbon and nitrogen density of vegetation and soil. The composition of carbon and nitrogen pools in Henan grassland ecosystems was the result of a combination of plant species abundance and distribution uniformity.
    Effects of biochar on Sb accumulation and biochemical characteristics of Lycopersicum esculentum in Sb-contaminated soil.
    ZHANG Huan, HUA Li, LUO Ting
    2019, 38(4):  983-994. 
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    Sb-contaminated soils incubated with/without wheat straw-derived biochar (SBC) and fruit tree-derived biochar (FBC) were used to plant Lycopersicum esculentum. Sb- fractions in soil were measured by sequential chemical extractions. The correlation between the contents of Sb fractions in soil and the accumulation of Sb in L. esculentum was analyzed. The chlorophyll content, antioxidant system,and root cell morphology of L. esculentum were investigated to examine the effects of biochar on biochemical characteristics of L. esculentum in Sb-contaminated soil. Compared to the control, the accumulation of Sb was decreased by 66% (P<0.01) in treatment with 10% SBC and 32% (P<0.01) in treatment with 10% FBC, respectively. Sb accumulation distribution was in order of root>leaf>stem for all treatments. Sb fraction was changed by biochar, and FBC had greater effect on Sb fraction than SBC. The correlation analysis showed that the change of Sb fraction in soil induced by biochar affected the phytoavailability of Sb. Biochar increased chlorophyll content and CAT activity, while reduced SOD and POD activities of L. esculentum. Stressed root cell morphology by Sb was alleviated by biochar.
    Phospholipase is involved in the allelopathy of diterpenoid oridonin to Arabidopsis thaliana.
    AN Yan-huang, ZHAO Qi-an, CHEN Lu, ZHAO Min, ZHANG Li-huan, YANG Ning
    2019, 38(4):  995-1003. 
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    We investigated the allelopathy mechanism of the diterpenoid oridonin to Arabidopsis thaliana. The germination rate, seedling growth, electrolyte leakage (EL), malondialdehyde (MDA), and three phospholipase activities (PLA1, PLA2 and PLC) of four Arabidopsis thaliana lines (the Colombia ecotype WT, and three phospholipase deletion mutants pla1, pla2and plc1) were measured under different oridonin concentrations (10 and 60 μmol·L-1). The results showed that germination was inhibited by oridonin, and PLA1 and PLA2 participated in this process. The growth of root and hypocotyl showed a “lowpromotion and high-inhibition” effect. PLA1 was involved in the regulation of roots. PLC was involved in the regulation of hypocotyl. The activities of different phospholipases changed greatly under different oridonin concentrations. The EL and MDA increased and were positively correlated with treatment concentration and duration. The stimulation of EL by 10 μmol·L-1 of oridonin was regulated by PLA2. The stimulation of EL by 60 μmol·L-1 of oridonin was co-regulated by PLA1 and PLA2. PLA1 and PLA2 regulated the MDA accumulation under oridonin treatment. Our results showed that phospholipase involves in the allelopathy of diterpenoid oridonin to Arabidopsis thaliana. Different phospholipases have different roles in regulating the response of plant to oridonin during its growth.
    Stomatal and non-stomatal limitations on photosynthesis of flag leaf of medium mature indica rice at early earring stage under natural conditions.
    YE Zi-piao, ZHENG Zhou, KANG Hua-jing, WANG Fu-biao, AN Ting, DUAN Shi-hua
    2019, 38(4):  1004-1012. 
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    This study aims to explore the characteristics of stomatal and non-stomatal limitations on photosynthesis of flag leaves of medium mature indica rice (Oryza sativa) under natural conditions in Jiangxi. Leaf gas exchange of four rice cultivars (i.e.restorer line R7-35, sterile line Jingda 3S, F1 hybrid of Jingda 3S/R7-35, and CK 9311) at the early earring stage were examined using a LI-6400 portable photosynthesis analyzer. The light-response curves of net assimilation rate (An), stomatal conductance (gs), intercellular CO2 concentration (Ci) and stomatal limitation value (Ls) were measured. The results showed that the saturated light intensity (Isat) values, corresponding to the maximum An, for the four cultivars were 1500, 1800, 1200, and 1200 μmol·m-2·s-1, respectively. The gs of R7-35, Jingda 3S and 9311 increased with the increases of light intensity (I). At higher I levels, non-stomatal limitation played a major role in limiting An of the four cultivars. The I values corresponding to the minimum Ci were 1600, 1600, 1400, and 1600 μmol·m-2·s-1, respectively. The saturation I values corresponding to the maximum Ls were 1400, 1200, 1400, and 600 μmol·m-2·s-1, respectively. If the decrease ofCi and the increase of Ls were the main reasons for the decreases of photosynthetic rate, the criterion of stomatal factor would be biased. Cultivar 9311 showed a decrease ofCi with the increases ofI until reaching 1600 μmol·m-2·s-1, an increase of Ls with the increases of I until reaching 600 μmol·m-2·s-1, and a nonlinear increase ofAn with the increases of I until reaching 1200 μmol·m-2·s-1. These results indicated that a combination of Ci decrease and ofLs increase would not necessarily lead to a decrease in An. Accordingly, we propose a new criterion for determining non-stomatal limitation whether it had Isat and for determining stomatal limitation whether it had the maximum gs.
    Phytoplankton functional groups of Xin’anjiang River Basin (Anhui section) and its tributaries in flood season.
    HU Chang-yu, FANG Jian-xin, LI Wei, WANG Ya-kun, PENG Ting, WANG Li, QIAN Li-ping
    2019, 38(4):  1013-1021. 
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    To understand the characteristics of phytoplankton community structure in Xin’anjiang River Basin (Anhui section) and its tributaries, water samples were collected from 15 stations in both main stream and tributaries in flood season of 2016 and 2017. The functional groups were classified based on the phytoplankton community composition. The results showed that phytoplankton belonged to six phyla and fifty-five genera. Species in Bacillariophyta, Cyanophyta and Chlorophyta were in dominant groups. Higher relative abundance was found in Navicula, Gomphonema, Synedra and Cyclotella in Bacillariophyta, as well as Closterium in Chlorophyta and Euglena in Euglenophyta. There were some differences in phytoplankton community structure between different sampling stations and different years. Across all river stations, the dominant species could be classified into 27 functional groups, among which MP, D, B, J, P, Tb and W1 were distributed in all sampling stations. The MP, D, B and Tb functional groups had both higher frequency of distribution and higher relative abundance. The low or mesotrophic status of nutrients reflected by dominant phytoplankton functional groups had well correspondence with the measured water chemical parameters. Water quality in studied stations fell between type I and type III, with a few stations falling to type III. Results of redundancy analysis (RDA) showed that NH3-N, TN, TP, and CODMn were the key environmental drivers determining the dominant  phytoplankton groups. Our results suggest that phytoplankton functional groups can indicate the habitat characteristics of Xin’anjiang River Basin and its tributaries. Combining phytoplankton functional groups and water chemical parameter measurement can provide sound data and basic theory for water quality monitoring and aquatic ecosystem protection in Xin’anjiang River Basin.
     
    Nutrient dynamics of litter-soil system during litter decomposition in coastal wetlands of Jiaozhou Bay.
    XI Min, LI Mao-mao, CHEN Ting, LI Yue, KONG Fan-long
    2019, 38(4):  1022-1030. 
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    To classify the nutrient dynamics of litter-soil system during litter decomposition, a 52-day laboratory experiment was conducted to simulate the litter decomposition process of Spartina alterniflora, Suaeda glauca, and Phragmites australis in coastal wetlands of Jiaozhou Bay. The contents of organic carbon (TOC), nitrogen (N) and phosphorus (P) in litter and soil were measured. The results showed that carbon loss of S.alterniflora, S. glauca, andP. australis litter after 52-day incubation accounted for 24.44%, 74.20%, and 49.75% of the initial total C contents, respectively. There was a net C accumulation in the soil. Nitrogen in the S. alterniflora litter had a net accumulation, but an opposite trend was found in the S. glauca litter. In addition, N in the P. australis litter accumulated first and then released. The N loss accounted for 37.93% and 4.81% of the initial litter N content of S. glauca and P. australis, respectively. Nevertheless, N in soil had a net accumulation during incubation. Phosphorus had a net release both in litter and soil. The P release from S.alterniflora, S. glauca, and P. australis litter accounted for42.37%, 59.27% and 28.48% of the initial total P content, respectively. The dynamics of C, N, and P in litter-soil system were closely related to litter and soil properties, which were mainly determined by microbial activity and nutrient demand.
    Characteristics of carbon, nitrogen and phosphorus leaching from litters of typical vegetation types in eastern Liaoning mountain water conservation forests and affecting factors.
    CHENG Zhi-hui, LI Fa-yun, LI Hai-yan, ZHANG Ying, LI Xia, LIN Li-tao, SUN Xue-kai
    2019, 38(4):  1031-1040. 
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    To understand the characteristics of nutrient leaching of litter and its affecting factors in the water conservation forests, we investigated the leaching of litter C, N and P of typical forests (Acer mono, Quercus mongolica, Larix olgensis, and Pinus koraiensis forest) in the upper reaches of Taizi River, eastern Liaoning Mountain area and the effects of solution pH, temperature, and leaching time on it. The results showed that the total leaching amount of total C, N, and P accounted for 0.24%-1.28% of the dry mass and there were significant differences (P<0.05) in the leaching rate and leaching amount from litter among different vegetations, with the order on the leaching amount of Acer mono>Pinus koraiensis>Quercus mongolica>Larix olgensis. The TP leaching (47.71 mg·kg-1) was higher in Acer mono litter than other species. There was the lowest NO3--N (14.95 mg·kg-1) and TN release (82.50 mg·kg-1) in Larix olgensis litter among the four vegetations. The litter TN and TP release was increased with decreasing pH value and the DOC, TN and TP release from litter was increased with rising temperature. The optimal temperature for the litter NH4+-N and NO3--N release differed among four vegetation types. The time when leaching reached stable was 12-24 h, whereas Quercus mongolica litter took a longer time on NH4+-N, NO3--N and TN leaching than the others. Our results provided a basis for better understanding the characteristics of nutrient leaching from litter.
    C∶N∶P stoichiometry in roots, stems, and leaves of four mangrove species.
    FAN Yue, PAN Yun-long, CHEN Zhi-wei, LIN Han, XU Ran, WU Cheng-zhen, HONG Tao
    2019, 38(4):  1041-1048. 
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    We analyzed the C, N and P concentrations and stoichiometric ratios (C∶N∶P) in roots, stems, and leaves of Kandelia candel, Bruguiera gymnorrhiza, Aegiceras corniculatum and Acanthus ilicifolius in Zhangjiang Estuary, subtropical China. The C concentrations in stems and leaves were significantly higher than those in roots of K. candel, A. corniculatum, and A. ilicifolius. The N and P concentrations ofK. candel, B. gymnorrhiza, and A. corniculatum were the highest in leaves, followed by stems and roots. In A. corniculatum and A. ilicifolius, the variation coefficient of stem C concentrations was significantly lower than that of roots and leaves. The variation coefficient of N concentration in K. candel, B. gymnorrhiza, A. ilicifoliusand that of P concentration in K. candel, B. gymnorrhiza, A. corniculatumwere the lowest in leaves. InK. candel, B. gymnorrhiza, and A. ilicifolius, the variation coefficient of C∶N ratio was significantly higher in roots and stems than that in leaves. Among the four mangrove species, foliar and root P concentrations in A. ilicifoliuswere significantly higher than those in the other species, and stem P in A. ilicifoliuswas slightly higher than in the other species. The variation coefficients of C, N, P concentrations in roots and C and P concentrations in leaves were higher in A. ilicifoliusthan in other species. C∶N∶P ratio in leaves (151∶9∶1) of four mangrove species was significantly lower than that in roots (187∶4∶1) or stems (239∶5∶1), suggesting that ecological stoichiometry of leaves was relatively stable. Our results provide theoretical basis for the large-caleresearch of ecological stoichiometry of mangrove and a scientific guidance for the conservation and sustainable management of mangrove plants.
    Effects of silicon application on cadmium uptake and translocation of rice under cadmium stress.
    PENG Ou, LIU Yu-ling, TIE Bai-qing, DONG Si-jun, WEI Xiang-dong, LIU Xiao-li, ZHOU Xi-hong
    2019, 38(4):  1049-1056. 
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    Effects of four concentrations of silicon (Si0, Si1, Si2, Si3) on cadmium (Cd) accumulation in rice “Taiyou 390” under three Cd concentrations (Cd1, Cd2, Cd3) were investigated. The results showed that rice yield increased with the increases of Si concentration. The Cd concentration in various parts of rice significantly decreased. Si application significantly reduced the transport coefficient in different parts of the rice, prevented the transfer of Cd to the aboveground part, and reduced Cd concentration in rice wound fluid. Si application effectively prevented and controlled Cd absorption in rice, with the magnitude of such effects increasing with Si concentration. With the consideration of cost, corresponding amount of Si should be applied to the pollution degree of Cd in order to reach the limit standard of the pollutants in foods. Meanwhile, there was an interaction between Si and Cd stress on rice agronomic trait, Cd uptake and transport. Our results provide basis for scientific management and rational utilization of heavy metal contaminated soil by proper application of Si fertilizer, which has significance for the production of rice with suitable food safety.
    Simulation of greenhouse gas fluxes in rice fields based on DNDC model.
    ZHAO Miao-miao, SHAO Rui, YANG Ji-lin, ZHAO Fen, XU Ming
    2019, 38(4):  1057-1066. 
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    It is an arduous scientific task to understand the mechanism of land use change process affecting ecosystem biogeochemical cycles and to use models to simulate the impacts of land use change on greenhouse gas flux. Using the DNDC model, a biogeochemical process based modeling, and meteorological, soil and management data, we estimated the greenhouse gas fluxes of CH4, CO2, and N2O in both new and old rice fields. Compared with the observed data, the DNDC model performed better in the old rice fields (R2>0.89, n=40, P<0.01) than in the new paddy fields (R2> 0.79, n=265, P<0.01), indicating that the model has limitations in capturing the land use change effects on greenhouse gas effluxes. The model performed better for CH4 and CO2 than for N2O. Changing soil SOC concentration and pH value is not enough to fully capture the land use change effect on greenhouse gas emissions, suggesting that soil biota associated with land use change have to be considered in the future to improve the model. Using model to simulate the effects of land use change on greenhouse gas effluxes may contribute to the national greenhouse gas emission inventories and the formulation of greenhouse gas management policy.
    Isolation of Aspergillus niger SY1 and its role in bioleaching of heavy metals from contaminated river sediments.
    DIAO Wei-qiang, WANG Zu-wei, XU Zhe, YU Xiao-man, ZHANG Qian-ru, ZENG Xiang-feng
    2019, 38(4):  1067-1074. 
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    Bioleaching, especially heterotrophic bioleaching, is a promising way to reduce heavy metals in contaminated medium. However, such method has not been widely used in the treatment of contaminated sediments. In this study, the contaminated sediments were collected from the dredging of the Xihe River (Shenyang). A heterotrophic fungus named SY1 was isolated from the sediments and identified as Apergillus niger through morphological and molecular methods. Its growth and acid production characteristics, as well as its role in leaching heavy metals from contaminated soil were investigated using shake flask culture. The results showed that the sediments were seriously contaminated by Cd, with a concentration of 33.3 mg·kg-1 and mainly in the bioavailable state. A. niger SY1 well adapted to a wide range of temperature from 25 to 30 ℃ and optimal initial pH value of 6.0-7.0. A large amount of glucose acid and oxalic acid (as high as 14.7 and 6.4 g·L-1 respectively) was generated in the bioleaching process. Under the optimal conditions (sediment concentration of 20 g·L-1, sugar concentration of 100 g·L-1, and spore concentration of 2×107 ind·mL-1), 93.5% Cd, 11.4% Pb, 62.3% Cu and 68.2% Zn were leached out after incubating SY1 for eight days. Therefore, A. nigerstrain SY1 is a cost-effective and efficient bioleacher of heavy metals, which could be used in the remediation of heavy metal contaminated dredged sediments.
    Mercury concentration in hair and its influencing factors in residents of typical origins of aquatic products in China.
    DING Li, CHEN Min, ZHANG Chan-chan, YANG Guang-hong, YAN Hai-yu, LI Ping
    2019, 38(4):  1075-1082. 
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    To evaluate health risks of mercury (Hg) exposure for residents in typical aquatic production areas in China, a total of 139, 136, and 159 human hair samples were collected from Wuhan, Qingdao, and Xiamen, respectively. Total mercury concentrations (THg) in hair samples were measured and the influencing factors were analyzed. The median (P25, P75) of hair THg concentrations in the whole population (n=434) was 0.435 (0.262, 0.820) μg·g-1. The medians (P25, P75) of hair THg concentrations in Wuhan, Qingdao, and Xiamen were 0.392 (0.253, 0.611) μg·g-1, 0.305 (0.204, 0.478) μg·g-1, and 0.814 (0.445, 1.350) μg·g-1, respectively. 7.2%, 5.9%, and 40.3% of population from the three areas with hair THg concentrations exceeded reference value (1 μg·g-1) set by U.S. Environmental Protection Agency, respectively. The highest mean value of hair THg was obtained in Xiamen. There were significant differences of hair THg concentrations between Xiamen and Wuhan, and between Xiamen and Qingdao (P<0.001). There was a significant correlation between hair THg and frequency of fish consumption (P<0.001). Hair THg varied among different age groups, with the highest value in the age group of 36-65 years. The averaged odds ratio (OR) (95% CI) value of increasing hair THg in population with rice consumption was 6.47 (4.07-10.29) compared with the population without rice consumption. In conclusion, population in Xiamen is at high risk of Hg exposure, while the population in Wuhan and Qingdao are at low risk of Hg exposure.
    Spatial and temporal dynamics of vegetation in Xishuangbanna from 2001 to 2015 based on MOD13Q1 data.
    ZHAO Ju-chao, ZHU Yan-hui, DUAN Guo-hui, YANG Kun
    2019, 38(4):  1083-1092. 
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    Xishuangbanna, the largest rainforest region in China, is one of the most important biodiversity conservation areas in the world. Studying the temporal and spatial variations of vegetation in Xishuangbanna and its relationship with climate factors can provide scientific supports for environmental management. This study, based on MODISNDVI dataset, aims to assess the spatialtemporal dynamics and spatial autocorrelation distribution pattern of NDVI and its response to thermalmoisture factors in Xishuangbanna from 2001 to 2015. Spatial autocorrelation analysis, linearregression analysis and partial correlation analysis were carried out. From 2001 to 2015, annual NDVI showed a slowly upward trend, with a rate of 0.11%·10 a-1 and the most pronounced enhancement in 2011-2015. NDVI had a “season inversion” phenomenon, i.e., the lowest NDVI value occurred in summer. In the past 15 years, mean NDVI of Xishuangbanna was 0.875, with a pattern of “high in the east and low in the west”. The NDVI threshold within 0.85-0.9 accounted for the largest proportion of the area. From 2001 to 2015, the Global Moran’s I of NDVI was greater than 0.65, showing a significant positive spatial autocorrelation, but the degree of spatial agglomeration of NDVI had weakened and tended to be fragmented. In 2013, the spatial heterogeneity of NDVI was the strongest. There were differences in vegetation change across different climate types. In the north tropical zone, the areas with improvement and degradation accounted for 28.74% and 9.40%, respectively. In the south subtropical and mid-subtropical zones, the deteriorated area was slightly higher than the improved area. Temperature was the dominant factor driving vegetation growth in Xishuangbanna, which was positively correlated with NDVI from December to February of the following year. Precipitation from June to November was significantly negatively correlated with NDVI.
    Spatiotemporal differentiation of vegetation coverage in Qinhe Basin.
    YUAN Li-juan, BI Ru-tian, XU Li-shuai, ZHU Hong-fen
    2019, 38(4):  1093-1103. 
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    With four images of Landsat TM/OLI as data sources, fractional vegetation coverage (FVC) in Qinhe Basin was estimated by dimidiating pixel model, and the spatiotemporal changes of vegetation patterns from 1993 to 2016 were analyzed using transition matrix, geo-spectrum and center of gravity migration model. The spatial variation of FVC at different attitudes, slopes, and aspects were explored based on topographic factors. The results showed that, spatially, FVC was higher in the north and lower in the south, and the vegetation with higher FVC was mainly transformed from those with lower FVC. During 1993-2016, the FVC in the Qinhe Basin showed an increasing trend with no significant fluctuation. The sum of areas with significant improvement (55.99%) and slight improvement (10.13%) were greater than that of areas with significant degradation (7.31%) and slight degradation (4.59%), reflecting good vegetation conditions. The center of gravity for FVC was migrated toward the southeast with 2.05 km, with the migrations of higher and highest FVC being the most obvious. FVC values were significantly positively correlated with elevation and slope. The area with remarkable improvement increased and then decreased with elevation and slope. The favorable terrain of vegetation in aspect was the area of the northeast, northwest and southwest. Our results will be helpful to the control of soil and water losses and ecological restoration in the study area.
    Dynamic estimation of forest ecological benefits in Shaanxi Province.
    ZHANG Gang-gang, HUI Gang-ying, YANG Ai-ming
    2019, 38(4):  1104-1112. 
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    As a carrier of ecological benefits, forest resources determine the value and services they provide. Based on forest area and forest volume, and the corresponding material quantity and values of forest ecological benefits of the 6th and 7th National Forest Inventory (NFI) in each province of China, we established an optimal prediction model of material quantity and values of forest ecological benefits, and applied this model to estimate the dynamics of material quantity and value of forest ecological benefits of the 2nd to 9th NFI in Shaanxi Province. The results showed that y=aS+bV+c was the optimal prediction model of the material quality and values of forest ecological benefits. The material quality of forest ecological functions in Shaanxi Province exhibited an obvious rising trend, especially in terms of nutrient accumulation and atmosphere environmental purification. The growth rate was high during the 5th NFI, between 9.45% and 30.35%. The simulated total values of forest ecological benefits in Shaanxi Province during the period from the 2nd to 9th NFI were 1979.66×108, 2061.41×108, 2064.46×108, 2324.02×108, 3085.11×108, 2394.08×108 (the actual value of 6th NFI), 3510.69×108, 3896.77×108,4069.95×108 yuan·a-1 respectively, showing an increasing trend. Among all forest ecological functions in Shaanxi Province, water conservation and biodiversity conservation accounted for a large proportion, which were 40.52%-40.70%, and 23.08%-26.50% respectively, followed by carbon sequestration and oxygen release, soil conservation, atmosphere purification, with the smallest proportion for nutrient accumulation. The optimal prediction model objectively reflected the synergy between forest ecological benefits and forest resources, providing an easy and feasible way to effectively estimate the dynamics of material quantity and values of forest ecological benefits in Shaanxi Province, and thus support for promoting the implementation of ecological GDP and ecological compensation system.
    Spatiotemporal variations of net primary productivity in new wetlands of the Yellow River Delta.
    LU Guang, HAN Mei, XU Ze-hua, ZHU Ji-qian, NIU Xue-rui
    2019, 38(4):  1113-1122. 
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    Based on field investigation and remote sensing, the spatiotemporal variations and primary influencing factors of net primary productivity (NPP) of new wetlands in the Yellow River Delta in recent 20 years were examined by using the CarnegieAmesStanford Approach (CASA). The correlation between observed and estimated NPP was significant (P<0.001), with averaged relative errors between -21.96 and 8.16. The NPP increased from coast to inland, and decreased from the banks along the river. The mean value of NPP and total NPP showed a downward trend from 1998 to 2016. The variation of mean NPP was relatively small, but the total NPP varied greatly, with the greatest total NPP occurring in 1998 and the smallest in 2010. The variation of NPP was obvious across seasons. The mean NPP was 74.25 g C·m-2 in spring, 101.58 g C·m-2 in summer, 41.83 g C·m-2 in autumn, and 13.10 g C·m-2 in winter. The estimated mean values of NPP differed with vegetation types. The estimated NPP values of various vegetations followed the Form. Robinia pseudoacacia > Form. Phragmites australis & Willow > crop > Form. Phragmites australis & Miscanthus saccharifleus & Imperatacy lindrica> Form.Phragmites australis & Tamarix chinensis> Form.Tamarix chinensis> Form. Suaeda heteroptera > Form. Spartana anglaca & Spartina alterniflora > Form.Tamarix chinensis & Suaeda heteropter a & Imperatacy lindrica. The correlation coefficient between NPP and soil soluble salt concentration was -0.389 (P<0.01). Therefore, reasonable “salt suppression with water” model can reduce soil salinity and promote the accumulation of plant organic matter.
    Remote sensing phenology of Larix chinensis forest in response to climate change in Qinling Mountains.
    GUO Shao-zhuang, BAI Hong-ying, Huang Xiao-yue, Meng Qing, Zhao Ting
    2019, 38(4):  1123-1132. 
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    Tree species at alpine timberline are sensitive to climate change, which are ideal species for studying climate change and phenological change. Based on the double Logistic curve fitting method, we reconstructed the MODIS EVI2 time series images from 2000 to 2015 and extracted key phenological parameters of Larix chinensis forest, combined with climatic data of the Taibai Mountain meteorological station, and analyzed the phenology of the L. chinensis forest and its responses to climate factors. From 2000 to 2015, the beginning time of growing period of L. chinensis forest was on about 120th day, and the ending time of growth period was on about 288th day, with an average growing period of 168 days. The rate of change was -0.65 d·10 a-1 at the beginning of the growing season with an advanced trend, and it was 0.35 d·10 a-1 at the end of the growing season with a delayed trend, with a delayed trend of 0.99 d·10 a-1 for the whole growing season. The areas with negative correlation between the start phenophase of L. chinensis forest and the temperature and precipitation in the same period accounted for 73.11% and 61.25% of the study area, respectively, while the areas with positive correlation between the start phenophase and the potential evapotranspiration accounted for 65.17% of the study area. The end of phenophase was positively correlated with temperature, precipitation, potential evapotranspiration, sunshine and wind speed in the same period, with area rates of 74.91%, 72.87%, 78.14%, 68.60% and 64.74%, respectively. Temperature was the major factor affecting the advance of the phenological stage of L. chinensis forest, while temperature, precipitation and potential evapotranspiration were the major factors affecting the late phenology.
    Soil organic carbon concentrations and the influencing factors in natural ecosystems of northern China.
    CHEN Xin-tong, XU Tian-le, LI Xue-jing, ZHAO Ai-hua, FENG Hai-yan, CHEN Bao-dong
    2019, 38(4):  1133-1140. 
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    Soil organic carbon (SOC) is the most active component in terrestrial carbon pool. Small variations in global SOC stock could result in significant impacts on the atmospheric CO2 concentration and contribute to global climate change. In this study, we collected 528 soil samples at 77 sites from different natural ecosystems (desert, grassland, shrubland, and forest) in northern China. We compared the differences of SOC concentrations in different ecosystems and analyzed the influencing factors on SOC concentrations. The results showed that SOC concentration was the highest in forests, with an order: forest > shrubland > grassland > desert. The SOC concentrations were significantly positively correlated with mean annual precipitation, clay content, silt content, NDVI, and plant species richness, but negatively correlated with mean annual temperature, soil pH, and sand content. We found a positive but insignificant correlation between SOC concentrations and plant species alpha diversity. The variations of SOC concentrations were mainly driven by soil, climate, and vegetation factors at regional scale.
    Effects of simulated acid rain and ectomycorrhizal fungi on soil nutrient, soil aggregate and organic carbon fraction under masson pine (Pinus massoniana) seedlings.
    YE Si-yuan, CHEN Zhan, CAO Ji-xin, SHANG He
    2019, 38(4):  1141-1148. 
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    Two-year-old seedlings of Pinus massoniana were planted in acidified soils to explore the effects of acid rain and ectomycorrhizal fungi (EMF) on soil organic carbon content, soil aggregate composition and soil nutrient (N, P, K) contents. We set up three levels of simulated acid rain \[pH 5.6 (CK), pH 4.5, and pH 3.5\] and applied two ectomycorrhizal treatments (inoculated, noninoculated) in each level of acid rain. The pH 3.5 treatment significantly reduced the contents of available P, total P, available K, ammonium N, nitrate N and total N in soil, while inoculation with EMF effectively alleviated such negative effects of pH 3.5 treatment. Acidification treatment increased the content of microaggregates (<0.053 mm, 0.053-0.25 mm) and reduced the content of macroaggregate (0.25-2 mm). Compared with control (pH 5.6), the pH 3.5 treatment significantly deceased the contents of organic carbon fractions, especially those with 0.25-2 mm size aggregate. Inoculation with EMF significantly increased the content of organic carbon. Acidification treatment significantly decreased the contents of soil light-fraction organic carbon (LFOC) and heavy-fraction organic carbon (HFOC), whereas inoculation with EMF significantly increased the contents of LFOC and HFOC. Our results indicated that inoculation with EMF could alleviate the negative effects of acid rain stress on soil quality.
    Horizontal ecological compensation method for water resources in the ecological core area of central Hainan.
    CHEN Yi-chen, LI Shuo, XU Hui-jun, QIAO Xue
    2019, 38(4):  1149-1156. 
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    The ecological compensation of water resources in basin is an essential measure to promote the protection of local environment and the sustainable development of regional economy. Here, we applied remote sensing, GIS, and soil and water assessment tool (SWAT) to explore the problems and solutions related to horizontal ecological compensation of water resources in Qiongzhong LiMiao Autonomous County, an ecological core area of central Hainan. The GIS watershed structure analysis and overlay analysis were conducted to delineate the boundaries and scopes of Wanquan River basin, Changhua River basin and Nandu River basin in the lower reaches of Qiongzhong, and to identify the spatial relationships among counties (cities) within each basin. The subject components of ecological compensation implementation were further clarified. By using the SWAT hydrological model, the calculated mean total water supply to the downstream counties (cities) from Qiongzhong County was 4.373 billion cubic meters per year, and the water transfer from Wanquan River basin, Nandu River basin and Changhua River basin accounted for 74%, 14% and 12% of the total water supply, respectively. Based on the input accounting of a number of water environment ecological protection projects such as afforestation, comprehensive improvement of rural environment and water source protection as well as the opportunity cost calculation under the “two suspensions” policy implemented in Qiongzhong County, a cost-based mathematic model of the total amount of horizontal ecological compensation for water resources of Qiongzhong County was constructed. By considering basins first and then counties (cities), the compensation sharing distribution model was constructed based on the indicators of water supply for each basin and production water consumption for each downstream county (city). The horizontal ecological compensation shared by the downstream counties (cities) was calculated. Our results provide useful reference for the implementation of horizontal ecological compensation for water resources in river basins.
    Responses of grassland to climate change and human activities in the area around Qinghai Lake.
    LI Ling, ZHANG Fu-ping, FENG Qi, WANG Hu-wei, WEI Yong-fen, LI Xiao-juan, NIE Shuo, LIU Jie-yao
    2019, 38(4):  1157-1165. 
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    The actual (NPPA) and potential (NPPP) net primary productivity in the area around Qinghai Lake were calculated based on MODIS NPP data, meteorological data and Thornthwaite model. The difference between NPPP and NPPA was used to quantify the impacts of human activities on net primary productivity (NPPH). The temporal and spatial changes of grassland NPPA, as well as the effects of climate change and human activities on grassland were analyzed. From 2000 to 2015, the average NPPA was 176.93 g C·m-2·a-1. In addition, NPPA exhibited a generally increasing trend between 2000 and 2015. In terms of spatial distribution, NPPA increased gradually from west to east. 87.42% of the grasslands were restored, whereas only 12.58% were degraded between 2000 and 2015. For the effects of climate change and human activities on grassland restoration, the climate change, human activities and their combined effect of climate change and human activities contributed to 10.98%, 5.27% and 83.75%, respectively. For the effects of climate change and human activities on grassland degradation, the climate change, human activities and the combined effect of climate change and human activities contributed to 6.28%, 50.75%, and 42.97%, respectively. It is concluded that the grassland degradation in this area was mainly caused by irrational human activities, such as overgrazing, grassland reclamation and land cover change.
    Seasonal stratification of waters in the Shennong Stream of the Three Gorges Reservoir.
    HUO Jing, CUI Yu-jie, SONG Lin-xu, LIU De-fu, JI Dao-bin, HUANG Jia-wei, WANG Yao-yao
    2019, 38(4):  1166-1174. 
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    The ecological environment of Shennong Stream has been greatly changed since the impoundment of the Three Gorges Reservoir. The vertical stratification and seasonal variation of water temperature (WT), dissolved oxygen (DO), and chlorophyll-a (chl-a) were measured by field monitoring in Shennong Stream in 2016. The results showed that the surface water temperature varied from 10.6 ℃ to 32.4 ℃. The water temperature structure was greatly affected by the hydrodynamic conditions. The vertical water temperature structure was “stepped” in spring under the reverse current density from the surface of mainstream, “doublemixed” distribution in summer under the reverse current density from the middle of mainstream, and was changed into “half a U-shape” in autumn and winter under the reverse current density from the bottom of mainstream. The vertical distribution of DO and chl-a concentration was affected by water temperature stratification. The DO was significantly stratified in spring and summer. The vertical distribution of DO was affected by chl-a concentration in spring and by water temperature in summer. Our results provide reference for analyzing the change of habitat conditions of Shennong Stream and for water environment management and water resources utilization in the Three Gorges Reservoir area.
    Monthly and seasonal variation of PM10 concentration and its relationships with meteorological factors in Shapoutou of Ningxia.
    LI Long, WANG Xu-Fu, ZUO Zhong
    2019, 38(4):  1175-1181. 
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    PM10 concentration and meteorological factors in Shapoutou of Ningxia were monitored from January to December of 2017. The variation of PM10 concentration in different months and seasons were analyzed using stepwise regression. The effects of meteorological factors on PM10 concentration were examined. Results showed that PM10 concentration exhibited a markedly temporal variation, being highest in May, followed by April and June, and lowest in August and September. The seasonal variation of PM10 concentration followed the order: spring > winter > summer > autumn. PM10 concentration was influenced by meteorological factors. PM10 concentration decreased with increasing wind velocity when wind velocity was lower than 1.5 m·s-1, but with an opposite trend when wind velocity was higher than 1.5 m·s-1. PM10 concentration was effectively dispersed by north wind but accumulated by east wind. Rain had significant removal effect on PM10, with a reduction of 46.5% in rain event. PM10 concentration presented a highest value when the relative humidity was about 50%, and then gradually decreased with increasing humidity. As a whole, the PM10 concentrations were affected by different meteorological factors at different periods.
    Effects of water supply conditions in fishway entrance on migration behavior of Schizothorax prenanti.
    LUO Kai-qiang, KANG Zhao-jun, XIA Wei, SUN Shuang-ke, SHI Xiao-tao, LI Min-ne, XU Jia-wei, HU Xiao
    2019, 38(4):  1182-1191. 
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    The construction of water supply facility is one of the effective ways to improve the fishway efficiency. How different forms of water supply change the swimming strategy of fish and attract them to enter the fishway entrance is a hot topic. In this study, the migration behavior of Schizothorax prenanti was examined under three water supply conditions with different distances and discharges by designing a generalized model of a fishway entrance. The results showed that compared with the condition without water supply, fish passage rate was significantly improved (P<0.05) under the water supply by bypass channel with a horizontal distance of 1 m to the fishway entrance and another bypass channel in which the water flowed down from top with a horizontal distance of 0.65 m to the fishway entrance. By extracting the corresponding velocity field and turbulence field on the path of the successfully traced fish, the preferred flow velocity area of Schizothorax prenantiwas from 0.6 to 0.8 m·s-1 and they would escape from the high turbulence (greater than 0.04 m2·s-2). The low turbulence area (0.01 m2·s-2) was preferentially selected by fish for going upstream. This study verifies that the turbulent kinetic energy and velocity are important hydraulic factors affecting fish migration and provides reference for design and optimization of fishway entrance supply water.
    Effects of exogenous sulfur input on nutrient availability in soil-plant system of grassland.
    JIANG Yong, LI Tian-peng, FENG Xue, WANG Ru-zheng, ZHANG Yu-ge
    2019, 38(4):  1192-1201. 
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    Exogenous sulfur input is one of the most important factors that acidify grassland soils, which may inhibit mineralization of soil organic matter and facilitate organic carbon accumulation, but may contribute to the decomposition of carbonates in calcareous soils. Sulfur inputs enhance the availability of nitrogen and micronutrients (iron, manganese, copper, zinc and boron), decrease the availability of molybdenum, accelerate the leaching of exchangeable base cations, and reduce the availability of calcium, magnesium and potassium. Sulfur inputs increase the availability of phosphorus in calcareous and neutral soils, but decrease it in acid or strong acid soils. Exogenous sulfur inputs can improve the synergetic uptake of nitrogen and phosphorus by plants, and generally increase plant uptake of metallic micronutrients. Soil acidification induced by sulfur inputs might lead to plant manganese toxicity, which could increase plant manganese uptake but inhibit plant iron uptake. High inputs of exogenous sulfur and soil acidification can decline aboveground productivity and plant species diversity in grasslands. Low dose of sulfur input tends to improve aboveground productivity, but its effects on plant species diversity and community stability remain unclear.
    Research advances in microbial mechanisms underlying priming effect of soil organic carbon mineralization.
    WEI Yuan-yun, CUI Li-juan, ZHANG Man-yin, PAN Xu
    2019, 38(4):  1202-1211. 
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    Priming effect (PE) is defined as the changes of soil organic carbon mineralization after the inputs of external labile organic matter in short term. The PE is a natural phenomenon that occurs in various terrestrial ecosystems and plays an important role in soil carbon cycling. The responses of soil microbes to the inputs of external labile organic matter are the internal drivers for PE. The microbial mechanisms of PE included: (1) cometabolism of a group of microorganisms and extracellular enzymes in the presence of labile organic matter; (2) labile organic matter provides energy for the special microorganisms to degrade recalcitrant organic matter under nutrient constraint; (3) microorganisms preferentially utilize the readily degradable substrates which match their stoichiometric demands. There is no consensus on those mechanisms and on the dominant soil microbes in the PE. Besides, the decomposition of soil organic matter and external organic matter is affected by the quantity and quality of external organic matter, all of which may influence PE. Soil temperature and moisture also affect the PE, but their importance may be less than external organic matter. In view of the existing controversy and deficiency about the PE studies, we propose that future research should adopt new methods to further clarify the contributions of various microbes to the PE, and should focus on the imbalance between microbial demand and external organic matter in order to promote the integration and development of the PE studies and the theory of ecological stoichiometry.
    Progress in study and application of remediation of heavy metals in sewage sludge by turf.
    LU Min-ying, BAO Xiao-dong, WU Xing-fei, SHAO Lu-ze, ZHANG Jie-yu, LI Fei-li
    2019, 38(4):  1212-1220. 
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    Phytoremediation has great promise for cost-ffective and eco-riendly remediation of contaminated soils. With huge production and high nutrient contents, municipal sewage sludge can serve as promising garden cultivation matrix for plant growth, which is beneficial to lessen its disposal cost and minimize the risk of heavy metal pollution. In this review, the regional distribution and speciation characteristics of heavy metals in composting sludge are discussed. Moreover, the growth characteristics of turfgrass, their abilities of heavy metal enrichment and influencing factors are presented. This review will provide a technique support for the remediation of heavy metals in sewage sludge by turfgrass, and is of great significance for resourcfulization of sewage sludge.
    Direct and indirect effects of habitat conditions on plant community in Horqin Sandy Land based on SEM.
    CAO Wen-mei, LIU Ting-xi, WANG Guan-li, LUO Yan-yun, FU Qing-yun
    2019, 38(4):  1221-1229. 
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    Due to the complexity and diversity of ecosystems, it is difficult to quantify the impacts of habitat conditions on the formation and succession of plant community. Here, we collected samples from 55 patches of wet meadow and from 278 patches of sand dune from Horqin Sandy Land located in the southeast of the West Liaohe River Basin. The relationships between plant communities and habitat conditions at different scales (wet meadowsand combination patches and individual sand dune patches) were evaluated by a mixed structural equation model, with the structural equation being analyzed by the partial least square method. In the wet meadowsand combination patches, the direct factors with significant effects on plant communities were soil structure, soil water content, and groundwater depth sorted by effect size, with the path coefficients of 0.607, 0.230, and -0.224, respectively. In the individual sand dune patches, thedirect factors with significant effects on plant communities were soil structure, soil water content, and soil organic matter (SOM) content sorted by effect size, with the path coefficients of 0.399, 0.224, and 0.206, respectively. When the direct effect of groundwater depth on plant community was significant, the direct effect of SOM content on plant community was insignificant, but with indirect effects on plant community indirectly by affecting soil structure. The direct effects of slope and elevation on soil quality were opposite at both scales, and the effect of slope direction was not significant. By constructing a latent variable of vegetation pattern in the structural equationmodel, we can infer the dynamics of community succession in the study area.
    Prediction of potential suitable distribution of Davidia involucrata Baill in China based on MaxEnt.
    WANG Yu-sheng, WANG Zhao-hai, XING Han-fa, LI Jing-wen, SUN Shuo
    2019, 38(4):  1230-1237. 
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    Davidia involucrataBaill is a rare and precious tree species in China. The prediction of its suitable habitats can provide important reference for its protection and research. Based on 387 sample distribution and 27 environmental factors in China, the MaxEnt model and geographic information system (GIS) were used to predict the potential suitable habitats. The accuracy of the model was verified by receiver operating characteristic curve (ROC). The results showed that the mean value of the area under ROC curve was 0.951, and the accuracy of the model was high, which was suitable for predicting potential suitable habitats of D. involucrata. The potential suitable habitats for D. involucrata were mainly located in Sichuan, Yunnan, Guizhou, Hunan, Hubei, Chongqing, Shanxi, and Tibet. The highly potential suitable habitats distributed in an irregular circular shape, with the Hengduan Mountains to the west, the Qinling WudangJinshan Mountains to the north, the ZhangjiajieXuefeng Mountains to the east and the south to Guiyang. In addition, they are also distributed in the Yarlung Zangbo River Valley in the southeast of Tibet and the Dabie Mountains in western Anhui. The major factors determining the potential suitable distribution were annual temperature range, annual precipitation, minimum temperature of coldest month, diurnal temperature difference, and annual precipitation variation coefficient. Other environmental factors, such as topography, soil, hydrology, had limited influence on the distribution of D. involucrata.
    Determination of crop parameters for WOFOST model and its performance evaluation based on field experiment of spring maize in Jinzhou, Liaoning.
    CAI Fu, MI Na, JI Rui-peng, MING Hui-qing, FENG Rui, ZHANG Shu-jie, ZHANG Hui, ZHAO Xian-li, ZHANG Yu-shu
    2019, 38(4):  1238-1248. 
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    Correct parameters are the key prerequisite for the prediction of crop models. In this study, a series of important crop parameters including initial total crop dry weight (TDWI), specific leaf area (SLA), leaf area index at emergency (LAIEM), developing parameters and other physiological parameters were measured and determinated using the observation data and trialanderror method based on the experiment of different sowing dates for maize in Jinzhou during 2011-2015. The adaptability of those parameters in WOFOST model was evaluated by testing the simulation accuracy of growth periods, leaf area index (LAI) and the biomass of different organs of maize with the methods of correlation coefficient, relative error (RE) and root mean square error (RMSE). The results showed that mean simulation errors for antheses and mature stages with 80% and 75% of the total samples were 1.25 and 3.47 days, respectively. The explanatory abilities of simulation to observation for LAI and total aboveground production (TAGP) were 0.8412 and 0.8945, respectively. Besides, there were obvious interannual and sowing date differences for the model performances in simulating abovementioned variables and their simulation accuracy were lower in dry year. Specifically, the RMSEs of LAI and TAGP were 0.38 m2·m-2 and 9.40 kg·hm-2 in 2012 respectively when soil water content was under the suitable condition during the whole growing season, and were 0.44 m2·m-2 and 22.65 kg·hm-2 in 2015 when maize suffered longterm drought. Furthermore, the model performed worse when the sowing date was deviated from the normal range. The RMSEs of LAI and TAGP were 0.30 m2·m-2 and 15.19 kg·hm-2 for the optimum sowing date on 30 April and 0.43 m2·m-2 and 25.66 kg·hm-2 for the sowing date on 20 May. Our results provide an important reference for determining the crop model parameters of spring maize in northeast China.
    Ecosystem health assessment based on the framework of vigor, organization, resilience and contribution in Guangzhou City.
    YUAN Mao-ning, LIU Yan-xu, WANG Man, TIAN Lu, PENG Jian
    2019, 38(4):  1249-1257. 
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    A healthy ecosystem underpins the sustainable development of human. The health condition of an urban ecosystem can be used as an important monitoring index for assessing the sustainable development of a city. In this study, the assessment index system for ecosystem health was established under a framework of vigor, organization, resilience and contribution. The township was used as a spatial unit, and the ecosystem health of Guangzhou City was evaluated based on land use data (level II) in 2000, 2005, 2010, and 2015. The results showed that the overall health condition of the ecosystem was not optimistic in Guangzhou City. Less than 1/5 of the towns were healthy and relatively healthy in 2015. From 2000 to 2015, the healthy levels of 75% towns remained constant (with no improvement). The towns with significant enhancement or significant deterioration each accounted for only 1% of the total. The towns with enhancement and deterioration were 5% and 20%, respectively. During the study period, the numbers of towns dominated by singlefactor and doublefactor increased, while this value for threefactor or fourfactor decreased. Meanwhile, the number of towns dominated by nonfactor remained stable. Generally, the vigor of ecosystem of Guangzhou City had been improved but its resilience had obviously decreased from 2000 to 2015. The health condition of the whole ecosystem showed a downward trend, which was not conducive to the sustainable development of the urban ecosystem.
    Ecological function zoning in Bailongjiang Watershed of Gansu based on productionliving ecological function clusters.
    LIU Dong-qing, ZHANG Jin-xi, GONG Jie, CAO Er-jia
    2019, 38(4):  1258-1266. 
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    Land resources in mountainous areas are limited. Reasonable suitability evaluation of land development and functional zoning can comprehensively reflect spatial differences, which is conducive to the coordinated management of regional social and economic development and environmental protection. We quantitatively evaluated the suitability of the productionlivingecological (PLE) functions. Ecological function zone in the watershed was divided using ELI function clusters at township level. The results showed that the optimal and suitable areas of production function in the watershed ware 1894.36 km2 and 1789.13 km2, respectively, which together accounted for 28.78% of the total available area. The most suitable area and suitable area of living function were 568.10 km2 and 909.10 km2, respectively, together accounting for 11.54%. The suitability distribution of production and living functions had some overlap. The high suitability was mainly distributed in the northern part of Tanchang, the northeast of Wudu, and TanchangZhouquWudu section of the bothbank areas of Bailongjiang. The extremely important area and important area of ecological function ware 1776.49 km2 and 3594.21 km2, respectively,accounting for 41.96% of total area. They were patchily gathered in the mountainous areas of Diebu and Zhouqu, south of Wenxian and southeast of Wudu. According to the results of clusters, there were tradeoffs among ecological, production, and living function. The Bailongjiang Watershed could be divided into seven ecofunctional zones. We also proposed corresponding regulatory opinions. Our results provide reference for the scientific management and sustainable development of watershed land ecosystems.