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    10 August 2021, Volume 40 Issue 8
    Progress in remediation technologies of heavy metals contaminated soil: Principles and technologies.
    WANG Hong-bo, GOU Wen-xian, WU Yu-qing, LI Wei
    2021, 40(8):  2277-2288.  doi:DOI: 10.13292/j.1000-4890.202108.037
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    Soil contamination by heavy metals is one of the global environmental problems, which is a major threat to environmental quality, human health, and national food security. To mitigate the adverse effects of heavy metals contamination, a variety of soil remediation technologies have been developed based on fundamental knowledge of physical, chemical, and biological sciences in the past decades, aiming to reduce the concentrations or bioavailability of heavy metals. Here, we reviewed ten remediation techniques, including encapsulation, landfilling, soil replacement, electrokinetic remediation, thermal treatment, vitrification, soil washing, stabilization/solidification, phytoremediation, and bioremediation. The principles, technical feasibility, and applicable conditions of all the technologies were evaluated, and the merits and disadvantages were discussed. In addition, we proposed that the basic earth science could contribute to the remediating of heavy metals contaminated soils as a natural attenuation process. Finally, we pinpointed how to choose a suitable remediation technology and how to fulfill key knowledge gaps and to overcome practical challenges.
    Geochemical characteristics of Fe-Mn nodules with different sizes in soils of high geological background areas.
    JI Wen-bing, YANG Zhong-fang, YIN Ai-jing, LU Yuan-yuan, YING Rong-rong, YANG Qiong, LIU Xu, LI Bo, DUAN Yi-ren, WANG Jue, WANG Yi-zheng, YU Tao, WU Tian-sheng, ZHANG Qi-zuan
    2021, 40(8):  2289-2301.  doi:DOI: 10.13292/j.1000-4890.202108.007
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    Understanding the geochemical characteristics of different particle sizes of iron-manganese nodules in soils of high geological background areas is helpful to clarify the effects of iron-manganese nodules on the abnormal enrichment of heavy metals and the main controlling factors of heavy metal adsorption and fixation in soils in karst areas. The surface soil samples (0-20 cm) were collected in Nanning City and Daxin County in Chongzuo, Guangxi. The samples of iron-manganese nodules with different particle sizes (0.3-0.5, 0.5-1, 1-2, 2-4, 4-6, 6-8, and >8 mm) and corresponding soils (<2 mm) were screened out for chemical analysis. The main aims of this study were to examine the variation and controlling factors of heavy metals in iron-manganese nodules with different particle sizes, and clarify the distribution of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in iron-manganese nodules and corresponding soils. The results showed that Fe2O3 and Cr in iron-manganese nodules displayed synchronous dynamics, while MnO2 presented a synchronous dynamic with Cd, Cu, Ni, Pb, and Zn with changes of particle sizes. The characteristics of heavy metals with changes of particle sizes reflected the formation and growth process of iron-manganese nodules. Iron affects the geochemical behavior of Cr, while manganese affects the geochemical behaviors of Cd, Cu, Ni, Pb and Zn. We calculated the percentage of mass (PM) of iron-manganese nodules to the element concentrations in soil. The PM of iron nodules was in an order of Cr (47.76%) > Cd (24.91%) > Pb (18.44%) > Cu (16.26%) > Zn (14.77%) > Ni (10.41%), while the PM of manganese nodules was in an order of Cr (45.25%) > Cd (37.94%) > Pb (25.86%) > Cu (15.59%) > Zn (13.79%) > Ni (12.15%). Those results indicate that a large number of heavy metals in the soil of karst area are actually fixed by the nodules in the ironmanganese nodules, with quite low biological activities. Therefore, heavy metals fixed by the iron-manganese nodules in the total amount of soil should be deducted in the assessment of soil ecological risk in high geological background areas, which would be more scientific and accurate.
    Formation mechanisms of iron-manganese nodules in soils from high geological background area of central Guangxi.
    JI Wen-bing, YANG Zhong-fang, YIN Ai-jing, LU Yuan-yuan, YING Rong-rong, YANG Qiong, LIU Xu, LI Bo, DUAN Yi-ren, WANG Jue, WANG Yi-zheng, YU Tao, WU Tian-sheng, ZHANG Qi-zuan
    2021, 40(8):  2302-2314.  doi:DOI: 10.13292/j.1000-4890.202108.006
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    Iron-manganese nodules are widely distributed in karst soil with high geological background, the content of which is much higher than that in nonkarst soils. To better understand the formation mechanism of iron-manganese nodules in karst soil, the nodules in the soil (0-20 cm) of central area of Guangxi were collected. The formation process of iron-manganese nodules in the soil of high geological background area was examined via the optical microscope (OP), field emission scanning electron microscope (FESEM), and energy spectrum analysis (EDS), combined with the complex soil forming process in karst area. The results showed that there were two kinds of nodules in the karst soil, i.e., iron nodules and manganese nodules. Generally, the nodules were sub-circular to elliptical in shape, and the particle size ranged from 0.5 to 4.0 mm. There were two kinds of iron-manganese nodules, with or without banded structure. Manganese nodules were mainly composed of iron oxides and manganese oxides, while iron oxides were mainly distributed in iron nodules. Based on those findings and the process of karst soil formation, the formation process of iron and manganese nodules in high geological background soil is summarized: (1) in the process of soil formation in karst area, iron and manganese were aggregated in different levels, which provides rich material sources for the formation of nodules; (2) the seasonal dry-wet cycling climate conditions led to the alternation precipitation of iron and manganese, which enhanced the formation of nodules; (3) the micropore structure in the nodules can provide space for microbial activities and channels for material flow, the special climate and environmental conditions rich in organic matters and microorganisms accelerate the formation of iron-manganese nodules, and eventually form iron-manganese nodules that are widely deve loped in karst soils.
    Accumulation of heavy metals in agricultural soils and maize in a typical black shale area with high geochemical background.
    CHEN Zi-jie, XIAO Tang-fu, LIU Yi-zhang, XING Dan, YANG Jun, ZHU Zheng-jie, NING Zeng-ping
    2021, 40(8):  2315-2323.  doi:DOI: 10.13292/j.1000-4890.202108.009
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    The weathering of black shale is a vital contributor to the high background values of heavy metals (HMs) in soils in Southwest China. However, the accumulation characteristics and controlling factors of HMs in soilcrop systems are not well understood. We investigated the bulk contents and bioavailability of HMs and their transfer pattern from soil to maize in a typical black shale area with high geochemical background in Chengkou of Chongqing. The results showed that the accumulation factor of HMs in soils from the study area followed an order of Cd>Zn>Cu>Ni>Cr>Pb, with Cd, Zn, Cu and Ni exceeding the background value. Cd was the main HM contaminant in the study area. Average Cd content in bulk soils was 5.11 mg·kg-1. The soils were seriously polluted by Cd, withIgeo ranging from 1.35 to 7.04. 82% of soil samples were classified as heavy contamination based on Igeo. The Cd in these soils posted high ecological risk, with an averageEr of 1534. The contents of bioavailable Cd in the soils ranged from 0.001 to 1.51 mg·kg-1, with an average extractability of 6.14%. Extractability of Cd decreased with increasing soil pH in acidic soils, and slightly changed with pH in near-neutral soils. The accumulation of HMs in maize was low, with the total Cd contents ranging from 0.001 to 1.36 mg·kg-1. 14% of maize samples exceeded the safety threshold of cereal. There was no relationship between the contents of HMs in maize grains and their bulk contents in soils. The relationship between Cd content in maize grains and soil available Cd content depended on soil pH conditions.
    Pollution and ecological risk assessment of heavy metals in surrounding soil by nonferrous metal smelting with high geological background in Northwest Guangxi.
    QIN Xu-zhi, LUO Zhi-xiang, JI Wen-bing, LIANG Peng, SU Rong, LI Fang, LIU Xu, YIN Juan
    2021, 40(8):  2324-2333.  doi:DOI: 10.13292/j.1000-4890.202108.012
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    The carbonate rock distribution area in Guangxi is a typical area with high geological background of heavy metals in soils. The nonferrous metal smelting activities in this area further enhance heavy metal accumulation in soils. Clarifying the contribution of smelting activities and geological background to regional soil heavy metal pollution is critically needed. In this study, we examined the distribution characteristics and potential ecological risks of heavy metals (Cd, Hg, As, Pb, Cr, Cu, Zn, and Ni) in soils in a nonferrous metal smelting area with typical geological background. The source and contribution rate of heavy metals were analyzed by the traceability method. The results showed that the main pollutants were Cd, Zn, As and Pb, and that the areas with heavy excess of Cd in surface soil were at a state of intensive ecological risk. The smelting activities were the main sources of Cd, Hg, As, Pb, Cu and Zn in soil. The presence of Cr and Ni was mainly contributed to the high geological background. The contribution rates of geological background factors to Cd, Hg, As, Pb, Cr, Cu, Zn and Ni were 4.8%, 71.7%, 33.6%, 31.0%, 92.4%, 76.5%, 27.3% and 99.3%, respectively. The contribution rates of human factors were 95.2%, 28.3%, 66.4%, 69.0%, 7.6%, 23.5%, 72.7% and 0.7%, respectively. Our results provide support for accurately evaluating the risk of heavy metal pollution and formulating scientific prevention and control measures of soil heavy metal pollution in carbonate mining areas.
    Assessing heavy metal pollution and human health risk of paddy soil with high geological background of transportation and deposition.
    CHEN Jia-le, XIANG Man-cheng, TANG Lin-xi, ZHANG Chun-hua, GE Ying
    2021, 40(8):  2334-2340.  doi:DOI: 10.13292/j.1000-4890.202108.010
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    In order to evaluate the risks of heavy metal pollution in paddy soils with high geological background of transportation and deposition, we measured the contents of cadmium (Cd), copper (Cu),  lead (Pb) and zinc (Zn) in 31 pairs of rhizosphere soil and rice samples collected in DoumenXinhui districts of Guangdong Province. We applied influence index of comprehensive quality (IICQ) and health risk assessment models to assess soil heavy metal pollution and its human health risks. The results showed that the proportions of soil samples at clean, sub-healthy, moderately polluted and heavily polluted status were 22.6%, 41.9%, 3.2% and 32.3%, respectively. The non-carcinogenic risks of Cd, Cu, Pb and Zn in rice were relatively low, with hazard quotient (HQ) of all the four kinds of metals being less than 1. Among the four metals, Cd had the highest noncarcinogenic risk. The hazard index (HI) of four metals was about 1. Carcinogenic risk (CR) index of rice Cd was higher than 10-4, suggesting a high carcinogenic risk. The CR value ranged between 10-6 and 10-4 for rice Pb, indicating that the carcinogenic risk was at an acceptable range. Children’s noncarcinogenic risk and carcinogenic risk were higher than adults. Our findings provide data support for the rice safe production and soil pollution risk control in the areas with high geological background of transportation and deposition.
    Model constructions and validations for regional cadmium coupling relationships in soil rice grain.
    CHEN Jia-le, TANG Lin-xi, XIANG Man-cheng, ZHANG Chun-hua, GE Ying, CHEN Xiao-min
    2021, 40(8):  2341-2347.  doi:DOI: 10.13292/j.1000-4890.202108.011
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    In order to establish regional models for describing soilrice grain cadmium (Cd) coupling relationship, we collected 369 groups of data from literature to construct models, which used generalized linear model (GLM), gradient boosting machine (GBM), random forest (RF) and Cubist methods, with soil pH and total Cd content (Soil_Cd) as independent variables and Cd content in rice grains (Grain_Cd) as the dependent variable. The robustness of those models in the Grain_Cd predictions was evaluated using the measured data of soil pH, Soil_Cd and Grain_Cd. Results showed that GLM, GBM, RF and Cubist models showed similar performance, with all of their coefficients of determination (R2) being around 0.5. The measured Grain_Cd values were best matched to the prediction of the RF model (R2=0.534). Therefore, the RF model, which is based on machine learning, was capable to reasonably predict Cd content in rice grains at the regional scale.
    Water management and silicon fertilizer application mitigate the accumulation of cadmium and arsenic in rice.
    YAO Bao-min, WANG Shu-qing, LI Gang, SUN Guo-xin
    2021, 40(8):  2348-2356.  doi:DOI: 10.13292/j.1000-4890.202108.008
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    Guangxi is one of the main rice-producing areas in China. Due to the karst geomorphology, paddy field in Guangxi is often contaminated by cadmium (Cd) and arsenic (As), which are generally considered to be mainly of geological origin. Organic silicon (Si) fertilizer, a new type of silicon fertilizer, can effectively reduce the accumulation of heavy metals in plants. As our knowledge about Cd or As mitigation by Si fertilizer was mainly based on results from pot experiments, little is known about the effects of Si fertilizer in plot and field conditions. In this study, both plot experiment and field experiment were carried out to investigate the mediating effects of Si fertilization on Cd and As accumulation in rice in the two growing seasons of one year. The dual effects of water management and organic Si application were also explored in the plot experiment. The results showed that Cd concentration in early rice (0.33±0.04-0.43±0.11 mg·kg-1) was significantly lower than that in late rice (0.77±0.02-1.27±0.13 mg·kg-1), while the As concentration in grains (0.44±0.01-0.49±0.06 mg·kg-1) in early rice was significantly higher than that in late rice (0.10±0.01-0.10±0.02 mg·kg-1). The application of Si fertilizer substantially reduced Cd accumulation in rice, but did not affect As accumulation. Field drying increased Cd concentration in late rice grains by 22%. Results from the field experiment further confirmed that the application of Si fertilizer reduced Cd concentration in early rice by 56% and late rice by 53%. Therefore, the accumulation of Cd in rice can be effectively controlled by flooding in the whole growing period and by applying Si fertilizer.
    Effects of spatial structure on species diversity in Pinus massoniana plantation of different succession stages.
    ZHANG Ya-hao, DIAN Yuan-yong, HUANG Guang-ti, LIU Xiao-yang, HAN Ze-min, JIAN Yong-feng, LI Yuan, WANG Xiong
    2021, 40(8):  2357-2365.  doi:DOI: 10.13292/j.1000-4890.202108.015
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    To examine the variations of stand spatial structure and species diversity and their relationship in masson pine plantations of different stages along the succession sequence, we set up 18 plots, including 6 plots of pure masson stand, 6 plots of mixed stand, and 6 plots of deciduous broadleaved stand. We analyzed the spatial structure and species diversity of trees, shrubs, and herbs using the quantitative indicators and the relationship between stand structure and species diversity using the Pearson’s correlation coefficient. The results showed that: (1) the degree of isolation for tree species was mainly affected by stand succession stage, which increased along succession sequence; (2) species diversity differed across succession stages, which was highest in the deciduous broadleaf stand, confirming the climax succession hypothesis; (3) species diversity was positively related by the degree of species mixing. These results indicate that successional stages determine the degrees of species isolation and species diversity within the community. Using deciduous broadleaved forest as the template of the study area, management practices such as tending and replanting can increase the degree of tree species isolation and species diversity, thus improving ecological services of masson pine plantations.
    Energy accumulation and distribution among vertical space of tree layer and at the ecosystem level of Chinese fir forests with different stand densities.
    WU Li-hua, DAI Lin-li, YE Yi-quan, LIU Li, CAI Shi-feng, FEI Yu-chong, LIN Kai-min, CAO Guang-qiu
    2021, 40(8):  2366-2377.  doi:DOI: 10.13292/j.1000-4890.202108.021
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    We explored the effects of different stand densities on calorific value in each component and the standing energy of community of Cunninghamia lanceolata under three stand densities (1800, 3000 and 4500 plants·hm-2), in Xinkou Teaching Forest Farm of Fujian Agriculture and Forestry University, Sanming City, Fujian Province. The distribution of calorific value and energy in each component of ecosystem was quantified by measuring calorific value and biomass. The results showed that, on the vertical space, calorific value and the standing energy of each component of C. lanceolata changed with height, while the standing energy of the trunk and bark decreased with increasing height. The calorific value of the remaining dead branches and leaves increased with increasing height, while standing energy of the remaining dead leaves increased and then decreased with increasing height. The calorific value and standing energy of other components did not depend on height. As for the roots of different diameterclasses, the calorific value and standing energy of stump were the largest, while those of fine roots were the smallest. The distribution of calorific value in each component and the standing energy of ecosystem showed close correlation with stand densities. The calorific values of remaining dead branches, remaining dead leaves, litter and roots increased with increasing stand densities, while the opposite was true for understory vegetation, fresh branches and fresh leaves. The calorific value of trunk, bark, and remaining dead leaves first increased and then decreased with increasing stand densities. The standing energy of ecosystem exhibited an increasing tendency with increasing stand densities. As for the standing energy in different components of the ecosystem across different stand densities, trunk accounted for the largest proportion, followed by roots and barks, and the proportion of other components were all less than 10%. The calorific values of fresh leaves, branches, and understory were significantly negatively correlated with stand densities, while the calorific values of other components were not correlated with stand densities. The standing energy of understory vegetation was significantly negatively correlated with stand densities, the standing energy of remaining dead branches and litter was significantly positively correlated with stand densities, while the standing energy of other components was not correlated with stand densities. In conclusion, from the perspectives of ecology, economics and longterm development, a stand density of 3000 plants·hm-2 is the most suitable for full use of biological resources and the growth of C. lanceolata.

     

    Sap flow characteristics of Prunus armeniaca L. and its response to environmental factors in Turpan Basin.
    MAHMOOD·Turup, ZHOU Wei-quan, DING Xiang, BAKRI·Rozi, ZULHUMAR·Tursun, LIAO Kang
    2021, 40(8):  2378-2387.  doi:DOI: 10.13292/j.1000-4890.202108.014
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    We measured the sap flow of Prunus armeniacaL. in Turpan Basin, using the PS-TDP8 pintype thermal diffusion probe technology, and recorded the meteorological factors of the orchard synchronously, with the aim to establish the relationship between sap flow and environmental factors. Results from this study can provide a basis for efficient and water saving cultivation of P. armeniaca in arid areas. The results showed that sap flow rate of P. armeniaca showed obvious diurnal variation. The peak value of sap flow rate occurred in June and July, being 0.71 and 0.78 g·s-1, respectively. The sap flow rate was higher on a sunny day than on a cloudy day, and the start-up time of sap flow on a sunny day was 1 h earlier than that on a cloudy day. The starting time of sap flow in summer was around 07:30-08:00, which was 1 h earlier than that of spring and autumn, with a long duration and large flow amount per unit time. Such changes caused the average unit time sap flow, daily average sap flow, and monthly sap flow of P. armeniaca being the largest in summer, which were 0.461 L·h-1, 11.062 L·d-1, and 331.68 L·month-1, respectively. The variations of air temperature, solar radiation, and water pressure deficit were basically consistent with the variations of sap flow rate, with a significant positive correlation between them (P<0.01). The variations of relative humidity were negatively correlated with the diurnal variations of sap flow rate (P<0.01). Stepwise regression models between stem sap flow rate and environmental factors were established. The model well fit the relationship between sap flow rate of P. armeniaca and environmental factors, with the coefficient of determination (R2) in each month was larger than 0.85 in the regression model. To sum up, the sap flow rate of P. armeniaca was quickened and transpirational water consumption was increased by strong solar radiation and high temperature in summer. Therefore, we should increase the irrigation frequency in summer days. The irrigation time should be selected before sunrise or after sunset to reduce water loss due to evaporation.
    Characteristics of hillslope runoff generation and its controlling factors on an alpine grassland in the Silin Co basin of the Tibetan Plateau.
    LIU Zhi-wei, LI Sheng-nan, GUO Yan-hong, MA Ning, ZHANG Yin-sheng
    2021, 40(8):  2388-2399.  doi:DOI: 10.13292/j.1000-4890.202108.029
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    Quantifying the relationship between precipitation and hillslope runoff is of great importance for understanding the rainfall runoff generation mechanism and the temporal and spatial dynamics of soil moisture. However, the hillslope runoff characteristics and its controlling factors in the central Tibetan Plateau remains poorly understood because of limited in situ observations, which impedes the understanding of land surface hydrological processes in this region with complex terrain. Based on a wide range of in situ observations of hillslope runoff, soil water and precipitation from a typical alpine grassland in the Silin Co Basin in the Tibetan Plateau, we investigated the hillslope runoff dynamics and elucidated the precipitation infiltration soil water storage runoff generation processes. By measuring soil water, land cover and precipitation, we quantified the runoff generation under different precipitation levels. The results showed that infiltration excess runoff was the main way for the generation of runoff in Silin Co Basin. For the light rain event of 7.6 mm, the runoff depth was 0.23 mm, and the water infiltration was 2.63 mm. For the medium rain event of 18.8 mm, the runoff depth was 0.68 mm and the water infiltration was14.65 mm. For the heavy rain event of 32.4 mm, the runoff depth was 0.78 mm and the water infiltration was 30.49 mm. For the rainstorm with rainfall of 55.4 mm, the runoff depth was 0.89 mm and the water infiltration was 47.59 mm. For those four sorts of rain events, the water infiltration occurred in the soil depth of 0-5 cm, 0-80 cm, 0-10 cm, and 0-80 cm, respectively. With a low soil water content (about 5%), the minimum rainfall that could generate runoff was 5 mm. However, with the relatively high soil water content (about 8%), the minimum rainfall that could generate runoff became 1.8 mm, and the runoff coefficient was approximately 0.016. The main factors controlling runoff coefficient were the maximum 10-min rainfall intensity and the initial soil water content.
    Effects of short-term nitrogen addition on plant community composition and stability of desert steppe.
    ZHANG Xin-wen, AN Hui, LIU Xiao-ping, WEN Zhi-lin, WANG Bo, DU Zhong-yu
    2021, 40(8):  2400-2409.  doi:DOI: 10.13292/j.1000-4890.202108.028
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    We conducted a nitrogen addition experiment in a desert steppe of Ningxia, northwestern China, to explore the effects of different addition levels (0, 5, 10, 20 and 40 g·m-2·a-1, designated as CK, N5, N10, N20 and N40 respectively) on plant species diversity, biomass, and community stability. Shortterm nitrogen addition significantly affected Shannon diversity index, Patrick richness index, and community coverage, but did not affect Pielou evenness index. The values of Shannon diversity index, Patrick richness index and community coverage reached the maximum under the N10 treatment, which were 2.05, 10 and 70.75%, respectively. The Pielou evenness index reached the maximum (0.92) under the N20 treatment. Shortterm nitrogen addition significantly increased aboveground, belowground, and total biomass of desert steppe, but significantly reduced the roottoshoot ratio at community level. Shortterm nitrogen addition improved community stability of desert steppe, with higher community stability under medium nitrogen addition treatment (N10). Therefore, plant diversity, biomass and community stability could be increased by nitrogen addition with a proper level.
    Changes of extreme climate and its effect on net primary productivity in Inner Mongolia.
    REN Jin-yuan, TONG Si-qin, BAO Yu-hai, GUO Xiao-meng
    2021, 40(8):  2410-2420.  doi:DOI: 10.13292/j.1000-4890.202108.030
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    Inner Mongolia is an important ecological security barrier for northern China. It is of great significance to understand the changes of extreme climate and its impacts on the net primary productivity (NPP) for the prevention of climate disasters and ecological protection. In this study, based on temperature and precipitation data and MODIS NPP data in Inner Mongolia, the temporal and spatial variations of extreme temperature and precipitation events and their effects on NPP were analyzed using linear trend analysis, GIS and correlation analysis. The results showed that the indices of both extreme high temperature and extreme precipitation showed an upward trend, while the index of extreme low temperature witnessed a downward trend. From 2000 to 2017, the annual NPP of Inner Mongolia increased significantly, with the greatest increase in eastern regions. The NPP in Inner Mongolia was more affected by extreme precipitation than extreme temperature, with the influence of extreme precipitation depending on vegetation types. Specifically, the extreme precipitation event had the greatest impacts on desert steppe, followed by typical steppe, shrubland, gobi desert, sandy vegetation, and field crops.
    Physiological and ecological adaptation strategies of Vallisneria natans to different water depths and sediments.
    WANG Lei, HU Xiao-qing, ZHANG Zhuo-lun, GAO Yu-xuan, ZHANG Xin-hou, WANG Guo-xiang
    2021, 40(8):  2421-2430. 
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    Submerged macrophytes are important primary producers in shallow lakes, with water depth and sediment type as the key factors affecting their growth. Vallisneria natans is a common submerged macrophyte in shallow lakes in the middle and lower reaches of the Yangtze River. The effects of water depth and sediment type on the growth of V. natanshave been reported, but the physiological traits of V. natans leaves are seldom examined. In this study, two sediment types (sand and mud) were used to plant V. natans at three water depths (40, 120, and 200 cm) to explore the ecological and physiological adaptation strategies of V. natans. The results showed that V. natansadapted to shallow water (40 cm) and deep water (200 cm) by changing plant height, ramet number, and leaf number, increasing antioxidant enzyme activity, and reducing chlorophyll concentration. V. natanshad low antioxidant enzyme activity but high chlorophyll concentration at the medium water depth (120 cm). Sediment types affected the growth of V. natans. The height, number of leaves, and ramets of V. natans were generally higher in the mud than in the sand. The chlorophyll concentration of V. natansin the mud at a water depth of 40 cm was higher than that in the sand, while the chlorophyll concentration of V. natans in the sand was higher at water depths of 120 and 200 cm. Sediment type did not change the antioxidant enzyme activity of V. natans. Our results indicated that 40-120 cm water depth and mud sediment were more conducive to the growth of V. natans than the other conditions. V. natansused different physiological and ecological adaptation strategies under different water depths and sediment conditions, which are of great significance to the restoration of submerged vegetation and the construction of freshwater ecosystem.
    Effects of freezing stress on different varieties of wheat during overwinter period in Huang-Huai area.
    YU Wei-dong, WU Lu, FENG Li-ping, HU Cheng-da
    2021, 40(8):  2431-2440.  doi:DOI: 10.13292/j.1000-4890.202108.033
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    Freezing injury is one of the common agrometeorological disasters in winter wheat production. The risk of winter wheat freezing injury during overwintering was not reduced with the increased winter temperature under climate warming. In this study, field acclimated seedlings and freezing chamber process were combined in a controlled freezing experiment for one day treatment. Three winter wheat cultivars were used in this experiment, including winterness wheat (Nong 211, ND), semiwinterness wheat (Zheng 366, ZM) and weakspring wheat (Yan 4110, YZ). The treatment temperature for ND and ZM was -8, -9, -10, -12 and -15 ℃, while the temperature for YZ was -6, -9, -10, -12 and -15 ℃. The results showed that no plants were killed in ND when temperature was above -15 ℃, while 58.3%–66.7% and 100% of plants were killed in ZM and YZ when temperature was between -15 ℃ and -12 ℃, respectively. Relative stem loss rate of ND and YZ significantly increased at -10 ℃, while that of ZM significantly increased at -9 ℃. When relative stem loss rate reached 50%, the critical temperature was -14.6 ℃ (ND), -11.3 ℃ (ZM) and -10.0 ℃ (YZ). The relative stem loss rate could thus be used as an index to identify the freezing tolerance of winter wheat in Huang-Huai area. Compared with the control, dry matter weight of each plant in the milk stage was significantly reduced due to low temperature stress below -12 ℃. However, the low temperature stress did not affect the net photosynthetic rate of leaves in the flowering stage. Moreover, grain yield of the three cultivars decreased under low temperature stress, while the yield loss rate increased with the decreased temperature. The yield loss rate and relative stem loss rate were ND < ZM < YZ at the same low temperature. Furthermore, the results of yield loss indicated that the decrease of spike number per unit area was the leading cause for the final yield reduction.
    Responses of seedling growth, yield of foxtail millet \[Setaria italic(L.) Beauv.\] and soil moisture to humic acid applications with different durations in dryland area.
    MI Jun-zhen, ZHANG Lan-ying, TIAN Lu, ZHAO Bao-ping, LI Li-jun, WANG Ying, LIU Jing-hui
    2021, 40(8):  2441-2449.  doi:DOI: 10.13292/j.1000-4890.202108.035
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    Drought seriously limits seedling emergence of crops, resulting in low and unstable crop yield in arid and semiarid areas in northern China. As a soil amendment, humic acid could resist drought and protect seedlings. Based on a field experiment, we investigated the effects of humic acid applications with duration of 1 to 5 years on foxtail millet emergence rate, dry matter accumulation, root length, antioxidant enzyme activity, and soil moisture at the seeding stage. Results showed that humic acid application increased soil moisture and soil storage water in the 0-60 cm layer at the seedling stage. All the treatments significantly increased emergence rate, above and belowg round dry matter accumulation, root shoot ratio, and root length at the seeding, with the increments ranging from 2.62% to 16.53%, 3.70% to 111.11%, 8.21% to 181.33%, 4.22% to 33.25%, and 2.00% to 23.87% respectively. Humic acid application significantly increased SOD, POD and CAT activities. Above ground biomass and grain yield increments ranged from 4.06% to 20.65% and 0.67% to 16.25%, respectively. The treatment with continuous application of humic acid for five years had the greatest effect, but there was no significant difference between the humic acid treatments continuously applied for four and five years. It is recommended to apply humic acid continuously for 4 years considering the actual production cost. Our results provide technique supports for combating drought and protecting the seedlings in dryland farming in the loess hilly-gully regions along the Great Wall in northern China.
    Spatiotemporal distribution of soil fungi in tropical rain forest in Hainan.
    DU Hao-nan, CHEN Wei, LAN Guo-yu, WU Zhi-xiang, YANG Chuan
    2021, 40(8):  2450-2459.  doi:DOI: 10.13292/j.1000-4890.202108.002
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    Soil microorganisms provide nutrients for plants by decomposing soil organic residues, which plays an important role in ecosystems. To clarify the composition and temporal and spatial variations of soil fungi in tropical rain forest of Hainan Island, we investigated soil fungi in dry season and rainy season of Diaoluo Mountain, Wuzhishan Mountain, Yingeling, Bawangling and Jianfengling rainforest in Hainan Province. The temporal and spatial variations of soil fungal community composition and diversity were analyzed based on high-throughput sequencing technique. The results showed that there were significant differences in fungal composition among tropical rain forests from different sites, and great differences in fungal diversity between the two seasons. Total nitrogen and total phosphorus concentrations were important environmental factors affecting the diversity of fungi in dry and rainy seasons, with an explanation rate of 13.07% and 17.86%, respectively. Collectively, soil fungal community in tropical rain forests has obvious temporal and spatial variations, which are mainly driven by soil nutrients.
    Fruit foods and potential seed dispersal by Hoolock tianxingat Gaoligongshan, Yunnan.
    LI Ning, QIAO Lu, WANG Qian-qian, RUAN Zhen-yuan, BAI Bing
    2021, 40(8):  2460-2466.  doi:DOI: 10.13292/j.1000-4890.202108.016
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    Primates are important vectors for seed dispersal in forest ecosystems. Foraging behavior and habitat use by primates could determine their contribution to the effectiveness of seed dispersal and forest regeneration. Hoolock tianxing is a flag species in Gaoligongshan, Yunnan, China. Information on fruit use and seed dispersal is needed to understand the role ofH. tianxingas a potential seed disperser and its contribution to forest regeneration. In this study, we investigated fruit food and seed dispersal by a family group of H. tianxingfrom October 2017 to December 2018. The results showed that H. tianxing foraged fruits from 33 species belonging to 26 genera, 21 families. Foraging frequency of fruits by H. tianxing varied among four seasons, with the highest foraging frequency in the autumn (from September to November). Fruit traits were the most important in affecting food use by H. tianxing. Small fleshedfruits and fruits with green or red color were preferred by H. tianxing. However, H. tianxing also feed on fruits with other colors during fruit-rich seasons. A total of 5099 intact seeds were found in 104 feces, with the density of Toddalia asiatica,Cayratia japonica,and Vaccinium mandarinorum seeds being significantly higher than that of other species. Our results indicated that H. tianxingplays an important role in seed dispersal for more than 10 plant species. Further studies should consider the role of H. tianxing in seed dispersal effectiveness and forest regeneration.
    Suitable distribution area for rare and endangered animals in Guangdong Hong-Kong-Macao Greater Bay Area.
    2021, 40(8):  2467-2477.  doi:DOI: 10.13292/j.1000-4890.202108.019
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    Rapid development of economic always leads to ecological destruction and biodiversity reduction. Here, based on the “Dual-Evaluation” guidelines issued by the Ministry of Natural Resources, the distribution data of 24 rare and endangered animal species and various environmental factors in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), combined with MaxEnt model and GIS spatial analysis, we simulated the suitable distribution areas of rare and endangered animals. The results showed that: (1) The value of the area under the receiver operating characteristic curve (AUC) of the MaxEnt model for three types of rare and endangered animal species reached or being higher than 0.89, indicating a high credibility of distribution simulation. (2) The results of Jackknife test indicated that the importance of different environmental variables varied across different types of animals. Precipitation in the driest season, land cover type, and the monthly average of diurnal temperature difference were the most important factors for the potential distribution of birds, mammals, and reptiles and amphibians, respectively. (3) The suitable area for the conservation and protection of animals in the GBA was 2998.84 km2, accounting for 5.27% of the total area of the GBA, and mainly located in Sevenstar Rock Park and Dinghushan in Zhaoqing City, Xiangtoushan in Huizhou City, Neilingding Futian National Nature Reserve in Shenzhen City, and the Maipo Nature Reserve in Hong Kong. Our results provide scientific basis for biodiversity conservation and the protection of wild animals in the GBA.
    Fisheries biology characteristics of Berryteuthis magister shevtsovi in the Sea of Japan.
    WANG Hong-hao, HE Tao, LU Hua-jie, CHEN Zi-yue, NING Xin, LIU Kai, CHEN Xin-jun
    2021, 40(8):  2478-2484.  doi:DOI: 10.13292/j.1000-4890.202108.026
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    Based on the samples of Berryteuthis magister shevtsovi collected in the Sea of Japan in December 2018, fishery biological characteristics were examined, including morphology, mantle length, body weight, sex maturity, stomach stage and fatness index. The result showed that the mantle length and body weight of B. magister shevtsovi in dominant group were 100-120 mm and 30-70 g respectively, while the mean values of fin length and width were (58.36±5.81) mm and (90.44±6.89) mm, respectively. For the relationship between body weight and mantle length, condition factor a and allometric growth factor b were 0.0007 and 2.3934, respectively, with mantle length growing faster than body weight. The maturation of gonads was dominated by individuals from stage I and II. When the mantle length was lower than 110 mm, the stomach stage was mostly at grade 1-2. The proportion of individuals with stomach stage at grade 3-4 increased when the mantle length was higher than 110 mm. The fatness index decreased with increasing mantle length. Our results provide reference for the future research on population identification, life history, development and utilization of B. magister shevtsovi.
    Fish community diversity and its relationship with environmental variables in Qili Lake wetland in Anqing.
    HU Min-qi, WANG Yin-ping, LIU Si-lei, ZHU Qing, LI Lian-xing, LI Pei-jie, LIU Kai
    2021, 40(8):  2485-2495.  doi:DOI: 10.13292/j.1000-4890.202108.032
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    To explore the effects of water level and temperature on fish community structure and diversity in Qili Lake, four surveys were carried out at high water level (wet season), flat water level (normal period I, II) and low water level (dry season) during 2019-2020, with environmental factors being measured. A total of 47 species were recorded in the survey, belonging to 4 orders, 10 families, and 36 genera. Cyprinids accounted for 65.96% of total species richness. More than 60% of the species were freshwater sedentary fishes, mainly dwelling in the upper and middle waters. The community was dominated by plankton feeding fishes, with Pseudobrama simoni asthe predominant species. The mean fish species richness in wet season and normal season was 35 species and 33 species, respectively, which were significantly higher than the 22 species in dry season (P<0.05). The average abundance of fish caught in the high water period was 1008, which was significantly higher than that of 662 fish and 594 fish in the low water period (P<0.05). The average weight of fish caught in different water periods showed no variation (P>0.05). The diversity index and richness index in the wet season were significantly higher than those in the dry season (P<0.05), but the dominance index was significantly lower than that in dry season (P<0.05). The results of cluster analysis showed that fish species composition in the dry season was classified into the group I, and that in the wet season and the normal season was classified into the group II, with a significant difference between both groups (P<0.01). In general, the diversity of fish community in the high water season was higher than that in the normal water season and the dry water season. Water level, water temperature, total phosphorus, and transparency were important environmental factors driving fish community structure (P<0.05).
    Sexual and male horn dimorphism in adult Xylotrupes socrates tonkinensis (Scarabaeidae, Coleoptera, Insecta).
    BAI Tian-qi, XIE De-hong, CHEN Yu-fu, ZHANG Cui-xian, WANG Yong-fen, WEI Chao-jun, WANG Mei-cun, YI Huai-feng, ZHANG Yong, NI Zhang-guang
    2021, 40(8):  2496-2505.  doi:DOI: 10.13292/j.1000-4890.202108.020
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    To elucidate the sexual and male horn dimorphism in adultXylotrupes socrates tonkinensis, multivariate statistical analysis was used to compare the differences of eight morphological traits between male and female, while allometry models of head horn length and thoracic horn length were used to determine the existence of horn dimorphism. The male-male competition behaviors of large and small males for females were observed in the laboratory. The results showed that the distributions of all traits, except tarsal length, overlapped considerably between males and females. The traits for males were generally larger than females (P<0.05). The coefficient variations of head horn length and thoracic horn length were 25.0% and 30.8% respectively, which were significantly larger than those of other measured traits. The values of head horn length and thoracic horn length followed normal distribution (P>0.05). The allometric relationships of head horn length and thoracic horn length to body size were fit with positive and simple linear models y=1.796x-2.8 (R2=0.765, P<0.05) and y=2.059x-2.628 (R2=0.951, P<0.05), respectively. Both small (head horn length <6.56 mm) and large males (head horn length>11.92 mm) that classified by probability grade could use horns to compete for females. Therefore, there is a sexual dimorphism. The head horn length and thoracic horn length of males had great variation, but without obvious horn dimorphism through allometric analysis. The dependence of reproductive strategies on body sizes of males needs to be further evaluated in the field.
    Simulation of watershed land use transition and eco-environmental effects under multiple scenarios based on production-ecological-living space.
    DENG Chu-xiong, PENG Yong, LI Ke, LI Zhong-wu
    2021, 40(8):  2506-2516.  doi:DOI: 10.13292/j.1000-4890.202108.031
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    It is of great significance to understand future land use transformation and the change of eco-environmental effect in a watershed for the development of territorial space planning and eco-environmental protection. Based on the land use data of Xiangjiang Watershed in the four periods from 2000 to 2015, we integrated FLUS model, eco-environmental quality index, and ecological contribution rate to quantitatively analyze the past and future land use transformation characteristics and changes of eco-environmental effect. During the period of 2000-2015, the land use transformation in Xiangjiang Watershed was mainly manifested as an increase of production and living land, but a decrease in ecological land. The ecoenvironmental quality of Xiangjiang Watershed decreased from 0.641 in 2000 to 0.637 in 2015. The occupation of forestry ecological land and agricultural production land by industrial and mining production land, urban and rural living land was the main reason for the eco-environmental deterioration. Under the 2030 baseline scenario and rapid development scenario, the area expansion of poor-quality zone, low-quality zone and medium-quality zone accelerated, and the ecoenvironmental quality dropped to 0.6334 and 0.6327 respectively, indicating a more severe ecoenvironmental deterioration. Under the ecological protection scenario, the trend of eco-environmental deterioration began to slow down, the ecoenvironmental quality increased to 0.639, and the area of high-quality area increased significantly. In general, the trend of eco-environmental deterioration in the Xiangjiang Watershed in the past 15 years was greater than that of eco-environmental improvement, and such trend would be intensified in the next 15 years. Simulating future land use transformation under multiple scenarios and quantitatively studying changes in ecoenvironmental effects can provide policy and decision-making references for territorial space planning and ecological control in the Xiangjiang Watershed.
    Temporal and spatial characteristics of green vegetation cover changes in the Yangtze River Economic Belt from 1982 to 2019.
    CUI Hao-nan, LUO Hai-jiang, ZHANG Xue-zhen
    2021, 40(8):  2517-2529.  doi:DOI: 10.13292/j.1000-4890.202108.036
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    We used two NDVI datasets (GIMMS3g NDVI and MODIS NDVI) and a monthly dataset of basic meteorological elements in China to analyze the temporal and spatial variations of vegetation cover in the Yangtze River Economic Belt, based on the average NDVI and its dynamics in the warm season (April–October) from 1982 to 2019. The contribution of climatic and nonclimatic factors to the spatiotemporal variation of vegetation cover was quantified. The results showed that, during 1982-2019, the average warm season NDVI of most regions in the Yangtze River Economic Belt was higher than 0.5, suggesting a favorable vegetation coverage. From 1982 to 2019, the average warm season NDVI of the Yangtze River Economic Belt showed a significant increasing trend, but with distinct stage characteristics. From 1982 to 1990, vegetation coverage significantly increased, with the dominant contribution of non-climatic factors. The typical areas in this stage included Sichuan, Central South and Northwest Yunnan, eastern Hunan, and Jiangxi. From 1990 to 2003, vegetation coverage was generally stable, but decreased in some particular locations. The intensity of the enhancement dominated by climatic factors was equal to that of the reduction dominated by non-climatic factors, which were basically offset. The typical regions with increases of climate-driven NDVI included southern Jiangxi, Chongqing and Guizhou, while the typical regions with decreases of non-climate-driven NDVI included Yangtze River Delta, Huanghuai Plain, plains of the middle and lower reaches of the Yangtze River, and Sichuan Basin. From 2003 to 2019, the vegetation coverage increased significantly, driven by both climate and non-climate factors, and with almost equal contributions. In general, the impacts of non-climatic factors on vegetation cover were greater than that of climatic factors during 1982 to 2019.
    Analysis of driving factors of vegetation NDVI change in Qilian Mountain National Park based on geographic detector.
    ZHANG Hua, LI Ming, SONG Jin-yue, HAN Wu-hong
    2021, 40(8):  2530-2540.  doi:DOI: 10.13292/j.1000-4890.202108.022
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    Vegetation is a key link connecting the atmosphere, pedosphere, hydrosphere and biosphere. The relationship between the spatiotemporal variation of vegetation and its driving factors is of great significance in the research on regional environmental changes. Based on the datasets of vegetation NDVI, climate, vegetation type, geomorphology, soil type, and DEM, we analyzed the spatiotemporal variation of vegetation NDVI and driving factors in Qilian Mountain National Park from 2000 to 2019 using a geographic detector model. The results showed that: (1) Vegetation in Qilian Mountain National Park had gradual improvement from 2000 to 2019; (2) The area with low and medium-low grade NDVI accounted for more than 55% of total area, the area of middle and high grade accounted for about 35%, and the proportion of high-grade area was extremely low. Meanwhile, the vegetation NDVI showed a downward trend from east to west; (3) Precipitation, altitude, soil type, and temperature were the main factors affecting the variation of vegetation NDVI; (4) There were interactions among the evaluation indicators on vegetation NDVI, which were doublefactor enhancement and nonlinear enhancement effects; (5) The most suitable scope or categories for vegetation growth in Qilian Mountain National Park were as follow: mean annual rainfall of 320.7-385.8 mm, moisture index of 2.9-21.3, mean annual temperature of 0.2-5.2 ℃, vegetation types of coniferous and broad-leaved forest, soil types of black and gray forest soil, DEM of 2875-3365 m, ≥10 ℃ accumulated temperature of 346.2-720.5 ℃, geomorphic type of medium undulating mountain, slope of 17.1°-22.8°, slope direction of 0°-31.55°.

     

    Spatiotemporal variation of grassland vegetation and its relationship with human activities in Qinghai Province in recent 40 years.
    WEI Xiao-xu, WEI Wei, LIU Chun-fang
    2021, 40(8):  2541-2552.  doi:DOI: 10.13292/j.1000-4890.202108.004
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    We analyzed the temporal and spatial changes of grassland vegetation cover and its response to human activities in Qinghai Province by trend analysis method, linear correlation analysis, and geographical weighted regression method, based on Landsat 8 OLI, GIMMS NDVI 3G data, MODIS data and statistical data from 1982 to 2018. The results showed that: (1) From 1982 to 2018, NDVImax of grassland in Qinghai Province showed an overall decreasing trend, with an average rate of 1.2×10-4. (2) The NDVImax was sensitive to grazing intensity in the southwest and central parts of Qinghai Province, while it was not sensitive in the northeast. This may be related to the complementary advantages of agriculture and animal husbandry and the implementation of ecological engineering. (3) The regression coefficients between NDVImax and per capita GDP, traffic, residential area, and total human population were 0.20, 0.11, 0.04 and 0.03, respectively. The local regression coefficients of per capita GDP and grassland NDVImax were high in the west and low in the east, while that for other regression relationships were high in the west and east and low in the east region. This is mainly due to the rich mineral resources in the west and a transportation hub and population gathering area in the east.
    Changes of fire and the relationship with precipitation in Amazon ecological area based on GEE.
    SHENG Yan-ling, ZHANG Yin, QIAO Ji-gang
    2021, 40(8):  2553-2562.  doi:DOI: 10.13292/j.1000-4890.202108.024
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    The fire happened in the Amazon in 2019 attracted worldwide attention. There are many problems to be solved with respect to the fire. Where exactly was the burning area concentrated? The duration and calamity degree also need to be explored. It is unclear whether there was a serious meteorological drought with less abnormal precipitation. Based on the MOD14A2 fire products, MCD64A1 burning sites, precipitation, surface cover types and other multi source data, we investigated the spatial and temporal variations of the 2019 fire in the Amazon using the geographic information system and remote sensing technology. The spatiotemporal correlation between the 2019 fire and precipitation was analyzed. The cause of fire was reasonably presumed using Spearman correlation coefficient and spatial correlation analysis method. The results showed that the fires in the Amazon had obvious temporal and spatial variations. Fires usually happened during the period from the end of July to the end of September, and were mainly distributed in Brazil and Bolivia in the southern part of the study area. Fires mainly occurred in the evergreen broadleaved forest and savanna. There was a significant negative correlation between precipitation and the number of fires with a delay of 1-2 months, which affected the temporal distribution of fires. However, the spatial correlation coefficient was close to 0, indicating no direct spatial correlation between precipitation and fire. Moreover, some fires were distributed in the area where human activities were frequent, which was probably related to human factors.
    Potential suitable distribution area of Quercus lamellosa and the influence of climate change.
    GUO Kai-qi, JIANG Xiao-long, XU Gang-biao
    2021, 40(8):  2563-2574.  doi:DOI: 10.13292/j.1000-4890.202108.023
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    The distribution and community composition of forest could be affected by rapid climate change. Understanding the suitable distribution range of dominant species in forest and the influence of climate change is the basis of forest resource protection and utilization. We used species distribution model to analyze the distribution dynamics of Quercus lamellosa Sm., an important tree species in semi-evergreen broad-leaved forest with endemic distribution in the Eastern Himalayas. A total of 54 distribution points of Q. lamellosa and eight environmental variables related to temperature and precipitation were collected. To simulate the potential distribution areas of Q. lamellosa in the past (Last Glacial Maximum, LGM), present, and future (2041-2060, 2081-2100), an ensemble model was developed using five species distribution models (Maximum Entropy Model, Artificial Neural Network, Generalized Linear Model, Generalized Additive Models, and Random Forest). The R and ArcGIS were used to estimate the change of the distribution area and centroid over time. The results showed that among those five models, the Random Forest performed the best and the score of Generalized Additive Models was the lowest. The true skill statistics (TSS) and the area under receiver operating characteristic curve (AUC) were 0.987 and 0.999, respectively, showing good simulation. Dominant environmental factors affecting the potential distribution ofQ. lamellosa were mean annual temperature and temperature seasonality. Currently, Q. lamellosais mainly distributed in the Himalaya-Hengduan Mountains. The current distribution area of Q. lamellosais one third less than that in LGM period, and would further decrease with future climate change. The centroid of theQ. lamellosasuitable area migrated northward with climate warming, and the migration speed was positively correlated with the extent of climate change. The potential distribution range of Q. lamellosais more reliable, as it was obtained by integrating analysis results of multiple models in this study. By demonstrating the distribution dynamics of Q. lamellosasuitable area, our results would provide reference for the maintenance of ecological stability and biodiversity conservation of semi-evergreen broad-leaved forest under the background of climate change.
    Potential distribution of invasive species Bidens frondosaunder different climate change scenarios in China.
    DU Zhi-xuan, SU Qi-tao, ZHOU Bing, YAN Xiao-hong, LI Xiao-hong, XIAO Yi-an
    2021, 40(8):  2575-2582.  doi:DOI: 10.13292/j.1000-4890.202109.023
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    Based on 237 distribution points and 19 climatic factors, the potential distribution of Bidens frondosa was predicted under three climate scenarios (RCP2.6, RCP4.5, and RCP8.5 (RCP: representative concentration pathways)) in current and future (2050s and 2070s) in China. The results showed that: (1) The main environmental factors affecting the distribution of B. frondosa were the precipitation of warmest quarter and the seasonal variation of temperature. (2) Under current climate mode, the suitable distribution area was 3501205 km2, accounting for 36.32% of the total land area in China. Except for Xinjiang, Qinghai, and Hainan provinces, other provinces (cities) are covered. (3) Under the future climate mode, the suitable distribution area increased by 107200-981500 km2 under the three scenarios, and reached the maximum (4482700 km2) in the RCP8.5 scenario in 2070s, and the suitable distribution area spread to the northeast of Inner Mongolia. In conclusion, under the background of global climate change, the suitable area of B. frondosa in China will increase and expand northward.
    The moisture-heat characteristics of different soil erosion micro-habitats in weathered waste dumps.
    WANG Dong-li, LI Jia, ZHANG Zi-qian, LIU Yang, XU Yuan, GUO Ying-ying, LYU Gang
    2021, 40(8):  2583-2592.  doi:DOI: 10.13292/j.1000-4890.202108.025
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    The objective of this study was to explore the mechanism of soil erosion micro-habitat underlying vegetation settlement at the slope surface of weathered waste dumps. We examined the characteristics and relationship of soil surface temperature, humidity, substrate temperature, and moisture in typical waste dump bare slopes, rills, shallow gullies and deposit bodies. The results showed that the diurnal variation of soil surface temperature in shallow gully erosion microhabitat was the greatest. The diurnal variations of temperature in vertical profile differed among different soil erosion micro-habitats, in that the surface temperature gradually increased from surface to bottom in the morning, decreased from surface to bottom at noon for bare slopes, rills and deposit bodies, but decreased first and then increased with increasing soil depth for shallow gullies. Furthermore, surface humidity of deposit bodies was the highest. The substrate moisture and capillary water holding capacity decreased in the order of deposit bodies > bare slopes > shallow gullies > rills. There were correlations between temperature, humidity and matrix moisture in hydrothermal characteristics. Thereinto, the substrate moisture and surface humidity for bare slopes were negatively correlated (P≤0.01). The unique water and heat distribution characteristics of shallow gullies might account for the difficulty in vegetation settlement. Therefore, our result that the variation of water and heat in different types of soil erosion micro-habitats is of practical significance to carry out effective vegetation restoration on weathered dry waste dumps.
    Biological and ecological characteristics of Cenchrus pauciflorus and the integrated control strategies.
    ZHOU Quan-lai, WANG Zheng-wen, QI Feng-lin, YANG Da-zhi, MEN Hong-yan, SUN Biao, QI Nan, CUI Xue, WANG Yong-cui
    2021, 40(8):  2593-2600.  doi:DOI: 10.13292/j.1000-4890.202108.013
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    Cenchrus pauciflorus, one of the malignant alien plant species, is distributed in the intersection of northwest Liaoning, eastern part of Inner Mongolia, and southern Jilin. It has caused serious impacts on grassland productivity, grassland quality, and biodiversity, due to its high resistance, high propagation capability, multiple dispersal routes, and high invasiveness. The effective measures on how to control the species are scarce. We reviewed biological characteristics, ecological characteristic, dispersal routes, harmfulness, and the current preventive measures. We analyzed the pros and cons of current preventive measures and proposed an integrated management strategy for the control of the invasive species. The future directions for theoretical research and development of control technology were prospected to provide basis for elimination of Cenchrus pauciflorus in northern China.
    Review on crop yield and nitrogen utilization in cereal-legume intercropping system.
    YU Xia, XIAO Shi-hao, LI Shu-juan, YANG Weng-ting, HUANG Guo-qin
    2021, 40(8):  2601-2609.  doi:DOI: 10.13292/j.1000-4890.202108.027
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    Cereal-legume intercropping is one of the main intercropping systems in traditional agriculture. With the rapid development of science and technology and the huge demands of grain production, scientists have further explored the mechanisms underlying crop yield and nitrogen utilizationadvantages of this typical intercropping system. We summarized the main research results of crop yield and nitrogen utilization in cereal-legume intercropping systems in the pastdecade. The effective mechanisms of intercropping promoting crop yield and nitrogen use efficiency were discussed from the perspectives of spatiotemporal niche, interspecific competition, root system interaction, and crop species. At last, we proposed that studies on the mechanization and intelligence in the whole season and rhizosphere soil microbial community should be strengthened in the cereallegume intercropping systems. This review would provide a reference for further research and application of cereal-legume intercropping systems.
    A review of the influence of habitat on emergent macrophyte growth and its feedback mechanism.
    FANG Yuan, XIE Pei, TAN Lin, SUN Yan-han, ZHU Shu-jing, QIAO Fei
    2021, 40(8):  2610-2619.  doi:DOI: 10.13292/j.1000-4890.202108.005
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    The ecological restoration of aquatic plants in wetlands is a hotspot in research area. Based on the habitat conditions of emergent macrophytes, we classified the habitat factors affecting emergent macrophyte growth into three categories, including main limiting factors, important constraining factors, and general influencing factors. Among these factors, water depth plays the most important limiting role on different growth stages of emergent macrophytes, with water demands varying among different growth stages. It is thus considered as the main limiting factor. Light, temperature, pH, nutrient, organic pollutant, and substrate have obvious impacts on the growth of emergent macrophytes. Each habitat factor has its specific range to meet the needs of optimal growth of macrophyte growth, which are the important constraining factors. The suitable ranges of water current, salinity, heavy metal, and biotic factor are relatively wide and have weak impacts, they are therefore considered as the general influencing factors. The growth of emergent macrophytes play important roles in purifying water quality, regulating microclimate, improving soil quality, and inhibiting algae growth. The management of emergent macrophytes should pay attention to the control of water depth and exogenous pollution input, the restoration and improvement of the habitat conditions of emergent macrophytes, and the rational construction of emergent macrophyte communities.
    Research advances on the endangered bird Mergus squamatus.
    LU Qing-bin, WANG Wei-bo, CHEN Yan-ji, XU Wei-nan, YANG Shu-zhen
    2021, 40(8):  2620-2634.  doi:DOI: 10.13292/j.1000-4890.202108.017
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    Chinese merganser (Mergus squamatus) is an endangered species with a long history. The progress in the research of Chinese merganser was systematically expounded in this review. The results showed that (1) For the population distribution: Russian Far East carried the main body of Chinese merganser breeding population, while China carried the main body of the wintering population. (2) For habitat selection: forest elements, water characteristics and concealment were the three factors determining habitat selection for Chinese merganser. (3) Behavior: behavior habits were mainly driven by temperature, sex ratio, and grouping characteristics. (4) Breeding ecology: nesting condition was one of the important factors limiting population breeding. (5) Endangered mechanism: the threatening factors included genetic diversity, self-habits and interspecific stress, and human activities were the main threat factor. (6) Conservation strategy: the habitat should be optimized according to the species’ habits and the conservation network should be constructed. Overall, current research mainly focused on ecology and related fields, forming the basic cognition of Chinese merganser. However, many conclusions were contradictory or generally speculative. Further research should be carried out from fidelity of wintering land, water area characteristics, and mating time. New technologies and ideas should be applied to deepen the understanding of Chinese merganser with multidisciplinary combination, so as to promote the effective protection of this rare species.

     

    Evaluation of forest health based on structural equation model.
    CAO Xiao-yu, WEI Xia, ZHAO Wen-fei, LI Ji-ping
    2021, 40(8):  2635-2647.  doi:DOI: 10.13292/j.1000-4890.202108.018
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    Index weight is a key factor in the evaluation of forest health. Exploring a scientific method for determining the index weight provides a new approach to evaluate forest health and a theoretical basis to improve the recognition of the evaluation of forest health. Here, we developed a structural equation model for assessing forest health of three typical forest types (Chinese fir pure forest, Chinese fir mixed forest, and natural secondary forest), in which forest structure, forest productivity, soil condition, and stand stability were set up as the firstorder factors and forest health as the second order factor. The index weight in the structural equation model was determined based on the conduction mechanism. The structural equation model was used to assess the health status of the three forest types. The results showed that: (1) For the structural equation model, the chi square degree of freedom (χ2/df) was 1.793, ranging 1-3; the root mean square error of approximation (RMSEA) was 0.079; the comparative fit index (CFI), normed fit index (NFI) and TackerLewis index (TLI) were 0.943, 0.908 and 0.929, respectively. The modelling results were compatible with the observed data. The structural equation model ran well and satisfied research requirements. (2) The index weights in the forest health evaluation system were 0.2515, 0.2263, 0.2277, and 0.2944 for forest productivity, forest structure, stand stability, and soil condition, respectively, indicating that soil condition was the key factor driving forest health. (3) The comprehensive scores of forest health for the examined three forest types ranged 2.1772-4.1708, indicating that the health status of the three forests were in the health, subhealth and medium-health status. In general, the health degree of the three forests ranked as natural secondary forest > Chinese fir mixed forest > Chinese fir pure forest. Our findings suggest that the structure equation model had advantages of extracting all information from original data and overcoming the multicollinearity uncertainties. The structural equation model provided a scientific basis and reasonable approach for the assessment of forest health. Results of health assessment showed that the three forest health evaluation indices could objectively reflect forest health status.
    Identification of selenium-enriched strain of bacteria and the optimization of conditions for selenium enrichment.
    WAN Ying-xin, ZHANG Jing, ZHANG Zi-xuan, GUO Zi-zhen, PENG Tian
    2021, 40(8):  2648-2655.  doi:DOI: 10.13292/j.1000-4890.202108.001
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    Microorganisms play a key role in selenium cycling. Many microorganisms could reduce Se(IV) and Se(VI) to less toxic Se(0) with the formation of Se nanoparticles (SeNPs), which are eventually exploitable in the fields of environmental remediation, biosensors, and medicine. It is of great significance to optimize the conditions of selenium enrichment for the application of selenium-enriched microorganisms. In this study, the strain WNJ40 isolated from Seladen soil was identified by sequence analysis of 16S rDNA technique, physiological and morphological characteristics. The effect of sodium selenite on the strain was observed by scan electron microscopy (SEM). Based on single-factor experiments, the response surface methodology was performed to design, optimize, and verify the selenium enrichment condition of strain WNJ40. The results showed that: (1) The strain WNJ40 was identified as Serratia marcescens. (2) Results of SEM analysis showed that spherical aggregations with diameters of 100-800 nm were produced when strain WNJ40 grew in the medium containing sodium selenite. (3) The optimal fermentation conditions were determined as: 8% of inoculation, 120 r·min-1 of rotation speed, and 58 h of fermentation time. Under the optimization conditions, selenium enrichment by the strain was248.70 mg·L-1, which was 22.74% higher than that before the optimization. Our results provide a theoretical and practical basis for the application of the strain.
    Correlation analysis between smartphone image parameters and nitrogen nutrition states of maize.
    WEI Xue, JIA Biao, LAN Yu, MA Sheng-li, MA Jian-zhen, JIANG Peng, SUN Quan
    2021, 40(8):  2656-2664.  doi:DOI: 10.13292/j.1000-4890.202108.034
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    The development of portable diagnostic methods for monitoring crop nitrogen nutrition can effectively monitor the nutritional status of maize, accurately recommend nitrogen fertilization rate, and quickly complete the nitrogen topdressing at different growth stages of drip-irrigation maize under the condition of integrated water and fertilizer. We used smartphone camera to obtain RGB images of maize under different nitrogen treatments from four-leaf stage to milkripe stage for two years, and calculated seven common color parameters. We analyzed the correlation between color parameters and plant nitrogen concentration (NP), constructed the model of plant nitrogen concentration and color parameter of smartphone image, and evaluated the accuracy of the model by the determination coefficient (R2),root mean square error (RMSE) and mean relative error (nRMSE). The results showed that nitrogen concentration of maize increased with increasing nitrogen application rates. In the six leaf stage, plant nitrogen concentration had a significant positive correlation with the normalized blueness intensity (NBI) and a significant negative correlation with the normalized difference yellowness index (NDYI). In the tasseling stage, plant nitrogen concentration was significantly negatively correlated with the normalized greenness index (NGI), red-green-blue vegetation index (RGBVI), and NDYI, while significantly positively correlated with the NBI. The relationship between plant nitrogen concentration and NDYI had the optimal fitting effect in the six-leaf stage, with the determination coefficients being 0.796 and 0.821 and the variation coefficients being 2.14% and 2.32% in the two years. At the tasseling stage, the fitting effect of the relationship between plant nitrogen concentration and NBIwas the best, with the determination coefficients of 0.836 and 0.773 and the variation coefficients of2.49% and 2.21% in the two years. The nitrogen nutrition diagnosis model for the plants was as follows: NP=5.38×NDYI-1.09 (R2=0.736) in six-leaf stage and NP=2.07×103×NBI3.31 (R2=0.791)in tasseling stage. The model validation results showed that R2 were0.734 and 0.790, RMSE were 0.363 and 0.746, nRMSE were 1.52% and 4.01%, respectively. TheRMSE and nRMSE values were relatively small, indicating that the model prediction accuracy was relatively high. Therefore, smartphone image parameters can be used to estimate nitrogen concentration of maize plants under drip irrigation in Ningxia, providing a theoretical basis for crop nitrogen nutrition diagnosis.