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    10 June 2016, Volume 35 Issue 6
    Effects of different silvicultural ways on soil nutrients and enzyme activity in larch plantation.
    ZHANG Jing-pu1,2,3, YU Li-zhong1,3*, LIU Li-fang1,3, ZHANG Jin-xin1,3, GAO Shang-lin4, ZHANG Wen-ru4, LIU Cheng-yu5
    2016, 35(6):  1403-1410. 
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    The aim of this study was to evaluate the effects of different silvicultural ways on soil fertility in the larch plantation. One 22-year-old larch stand was chosen and treated with four treatments (control treatment: 900 trees·hm-2, medium thinning treatment: 750 trees·hm-2, heavy thinning treatment: 450 trees·hm-2, clear cutting treatment: 0 tree·hm-2). Soil nutrients, soil enzyme activities in the top (0-10 cm) and subtop (10-20 cm) soil layers and their relationships were analyzed. Our results showed that (1) compared with the control, total carbon and total phosphorus in the top soil layer, and total carbon, total nitrogen, total phosphorus, and pH in the subtop soil layer significantly decreased in the heavy thinning treatment. In addition, total phosphorus in the top soil layer and total nitrogen and total phosphorus in the subtop soil layer significantly decreased after clear cutting. The heavy thinning and clear cutting treatments did not significantly change soil available phosphorus and inorganic nitrogen contents. (2) Compared with the control, the activities of phenol oxidase, exoglucanase and N-acetyl-β-cosaminidase significantly increased in the top soil layer under the medium thinning treatment, while acid phosphatase activity significantly decreased in the top and sub-top soil layers under the heavy thinning treatment and in the top soil layer under the clear cutting treatment. (3) Compared with the control, the specific enzyme activities (i.e., normalized to soil total C and N), including phenol oxidase, exoglucanase, β-glucosidase, and N-acetyl-β-glucosaminidase, significantly increased in both two studied soil layers under the medium and heavy thinning treatments. How-ever, there were no significant differences in phenol oxidase, exoglucanase, β-glucosidase, and N-acetyl-β-glucosaminidase activities between the control and clear cutting treatments, except for the phenol oxidase activity. (4) The results of correlation analyses showed that the studied enzymes were significantly related to total carbon, total nitrogen, total phosphorus, and inorganic nitrogen contents. In conclusion, medium thinning was more advantageous to sustaining soil fertility in the larch plantation.
    Spatiotemporal distribution of minimum temperature during autumn at different slope aspects of secondary forest gap in montane zone of eastern Liaoning Province.
    ZHU Cheng-yao1,3, WANG Yi3,4, LI Xiu-fen1,3*, LIU Jiang1, ZHANG Jin-xin2,3, WANG Tao1,3
    2016, 35(6):  1411-1419. 
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    Aiming to determine the change pattern of early frost in gaps of secondary forest ecosystem in montane zone of eastern Liaoning Province, the spatiotemporal distribution characteristics of the minimum temperature in forest gaps during autumn at different slope aspects were analyzed in this study. The results showed that there was a significant difference in the minimum temperature among gaps at three slopes (P<0.01). The highest values of minimum temperature occurred at the northeast slope in September (-4.61 ℃) and the highest values occurred at the northwest slope in October (-7.24 ℃). No significant difference was found in the minimum soil temperature at 5 cm depth among gaps at the three slopes (P>0.05). The lowest values of minimum soil temperature in September and October occurred in the northwest (4.87 ℃) and southeast (2.05 ℃) slope gaps, respectively. The spatial distribution of minimum air temperature in gaps and minimum soil temperature at 5 cm depth varied asymmetrically with time, and the high-value area existed at the gap edge. In early autumn (before 28 September), the minimum air temperature of the northwest slope and the northeast slope within gaps were higher than that of the southeast slope. In late autumn, however, the minimum air temperature of the northwest slope was the highest, and that of the northeast slope was the lowest. In addition, the air temperatures within gaps fell below 0 ℃ just after the early autumn, and the differences of the air temperature between different slope aspects were greater than those in the early autumn. Compared with the minimum air temperature, the minimum soil temperature was much higher, with smaller fluctuation, but their daily variation was similar. All these results indicated that the minimum air and soil temperatures within gaps varied with slope aspects, positions within gaps and time. The minimum air and soil temperatures influenced the frost dynamics and its level of damage. Thus, better understanding the spatiotemporal distribution of the minimum air and soil temperatures within gaps played a critical role in forest regeneration and succession.
    Influence of simulated nitrogen deposition enhancement on soil microbial community of different tree species.
    HUANG Xing-ran, GUO Ping-ping, WU Wang-wang, HU Bao-ye, YI Zhi-gang*
    2016, 35(6):  1420-1426. 
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    As decomposers, soil microbes play great roles in material circulation and energy flow in ecosystems. Elevated nitrogen deposition caused by human activities can directly or indirectly change the structure and function of soil microbial community, and then influence the material circulation and energy flow in ecosystems. From May 2012, nitrogen deposition was simulated in laboratory with ammonium nitrate at three levels monthly (5.6, 15.6, 20.6 g N·m-2·a-1) at the beginning of every month, and the effects of nitrogen deposition on soil microbial community structure were investigated by phospholipid fatty acids (PLFAs) method in the middle of April (rainy season) and October (dry season) 2013 with one pine species and three broad leaf species, namely Pinus massoniana, Ormosia pinnata, Schima superba and Acacia mangium. The results showed that with the increase of nitrogen level for all tree species, total soil microbial PLFAs decreased, but bacteria were still the dominant microorganisms. The soil microbial PLFAs in dry season were higher than those in rainy season at all the tested nitrogen levels for all the tree species. Soil microorganisms related significantly to soil water content, soil pH and total nitrogen. In rainy season, soil microbes were mainly influenced by the soil pH and soil water content, but by soil nutrient in dry season. Under the stress of nitrogen deposition, soil microbial PLFAs of nitrogen fixation plants (O. pinnata and A. mangium) were higher than those of the other two species. Sampling time, nitrogen levels and tree species all had significant influences on soil microbial (total soil microorganisms, bacteria, fungi and actinomycetes) PLFAs, but had no impacts on the ratio of fungal to bacterial PLFAs (F/B). The timing effect, the nitrogen deposition level and the effect of tree species should be taken into integrated consideration when studying the effects of nitrogen deposition on soil microorganisms, to provide a scientific basis for the environment protection and the sustainable development of ecological system.
    Effects of warming and N addition on ecosystem carbon exchange in a desert steppe.
    WU Qian, HAN Guo-dong*, WANG Zhong-wu, PAN Zhan-lei, LIU Fang, WANG Rui-zhen, ZHANG Rui-yang, QIN Jie, LI Jiang-wen
    2016, 35(6):  1427-1434. 
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    Global warming and atmospheric nitrogen (N) deposition are two of the most important global change drivers. In grassland ecosystem, increasing atmospheric temperature and nitrogen deposition are expected to modify the carbon sequestration; however, how warming and nitrogen addition affect ecosystem carbon exchange in the given conditions is unclear. The objective of this study was to assess the effects of global warming and N addition on C exchange of the desert steppe. A random split plot experiment (2×2 factors) in a desert steppe with dominant species of Stipa breviflora was conducted to mimic the climate warming using the infrared heaters and enrichment of nitrogen deposition by fertilizer addition. The gross ecosystem productivity (GEP), ecosystem respiration (ER) and net ecosystem exchange (NEE) were measured in different conditions. The integrated impact factors on ecosystem carbon exchange were analyzed during 2013 and 2014. The results showed that: (1) Warming significantly increased soil temperature and soil moisture about 0.70 ℃ (P<0.001) and 7.58% (P<0.001), respectively. (2) Warming, N addition and their interaction significantly increased the GEP and ER (P<0.05), but they had no significant effect on NEE (P>0.05). (3) In 2013, GEP peaked in early August, but ER reached peak during late August and early September, so NEE changed with GEP and ER. GEP, ER and NEE all peaked during late August and early September in 2014. (4) ER and GEP increased with the increasing air temperature and precipitation. Furthermore, soil temperature and soil moisture were also two of the most important factors affecting ecosystem carbon exchange.
    Effect of long-term fertilization on soil organic carbon pools in Mollisols of Northeast China.
    YUAN Ya-ru1, 2, LI Lu-jun2, LI Na2, YOU Meng-yang2, HAN Xiao-zeng2*
    2016, 35(6):  1435-1439. 
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    A study was carried out in a long-term field experiment to assess the influence of 19 years of application of mineral fertilizers and organic manure on soil organic carbon (SOC) pools of Mollisols in Northeast China. We used soil aggregate and soil organic matter fractionation techniques to isolate SOC pools (total coarse particulate organic matter (total cPOM), total fine particulate organic matter (total fPOM) and total silt and clay (total s+c)). We found that the application of chemical fertilizers alone did not affect SOC contents and the mean weight diameters (MWD) of aggregates, while combination of mineral fertilizers with organic manure facilitated the macroaggregation processes and greatly increased SOC content and stock by 36% and 18%, respectively, over the unfertilized control. Compared with the control, chemical fertilizer application had no influence on SOC pool and its stabilization, while integrated use of manure and chemical fertilizer significantly increased the SOC content located in total cPOM and total fPOM and thus decreased the stabilization of SOC pool. The increase of labile C in manure-added soils benefits the SOC mineralization to increase crop yield; on the other hand, it intensifies the greenhouse effect. Given these effects, application of manure at appropriate rates is a better way to solve the contradiction between agricultural production and environmental protection in Mollisols of Northeast China.
    Effects of nutrient addition on plant community composition and aboveground biomass in a marshy meadow in the Sanjiang Plain.
    CHEN Hui-min1,4, SHI Fu-xi1, YANG Gui-sheng3, ZHANG Xin-hou1, MAO Rong1,2*
    2016, 35(6):  1440-1446. 
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    In recent decades, the Sanjiang Plain has been experiencing excessive agricultural land reclamation from wetlands due to the increased demand for food production. Fertilizer applications during agricultural activities have dramatically increased nitrogen (N) and phosphorus (P) inputs to wetlands in these regions, which would markedly affect wetland ecosystem structure and function. In this study, we conducted a 3year nutrient addition experiment to examine the effects of increased N and P availability on plant community composition and structure, and aboveground biomass in a marshy meadow in the Sanjiang Plain, Northeast China. Our results showed that N addition (6 g N·m-2·a-1) significantly increased the dominance of grasses and decreased the dominance of sedges, and thus caused a decline in species diversity. Phosphorus addition (1.2 g P·m-2·a-1) significantly decreased the dominance of grasses and increased the dominance of sedges, albeit there were no changes in species diversity and aboveground biomass. Additionally, N and P addition did not produce an interactive effect on species diversity and aboveground biomass. Compared with the control treatment, combined N and P addition decreased species diversity, but increased plant aboveground biomass. These results imply that increased N and P availability have inconsistent effects on species diversity and plant productivity in the marshy meadow in the Sanjiang Plain. Moreover, our study suggests that nutrient enrichment would substantially alter species diversity and plant productivity in freshwater wetlands in Northeast China.
    Effect of deeply and concentrated straw returning on soil microbial community and melon root growth in continuously cropped greenhouse soil.
    GAO Qing-hai*, JIA Shuang-shuang, GUO Yuan-yuan
    2016, 35(6):  1447-1452. 
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    For the purpose of resolving the continuous cropping obstacle in greenhouse soil, the present study investigated the effects of two types of straws (corn straw and peanut straw) returning on the soil enzyme activities, soil microbial abundance and root growth of melon by preparing the straws in the furrowing and riding ways for continuous two years. The results indicated that straw returning markedly improved the soil pH and content of soil organic matter of continuously cropped soil. The content of soil organic matter was up to 17.08 g·kg-1 under the corn straw returning condition, with an increase of 12.8% compared to the control. Meanwhile, straw returning enhanced the activities of some soil enzymes, such as urease, sucrase and catalase. Straw application led to the increase of available potassium and available phosphorus, in spite of the decrease of available N. Additionally, straw returning led to the enriched soil microbial biomass, especially the soil microbial biomass under corn straw returning increased by 30.1% compared to the control. Straw returning increased the number of bacteria and actinomycetes, while decreased the number of fungi. Also, straw returning resulted in wellconditioned soil environment and thus promoted root growth, enhancing the root fresh weight and the root activity of melon. Notably, the fresh weight and the activity of melon root were 8.3 g·plant-1 and 70.4 μg·g-1 FW respectively under corn straw returning. The results suggested that the application of straws in the furrowing and ridging manners contributes to modifying the properties of continuously cropped greenhouse soil and promoting the root growth of melon, and corn straw returning exhibits better effects than peanut straw returning.
    Multi-scale characteristics of soil carbon and nitrogen in karst peak-cluster depression based on multivariate empirical mode decomposition.
    WU Min1,2,3, YE Ying-ying1,2,3, XIAO Shuang-shuang1,2,3, ZHANG Wei1,2, WANG Ke-lin1,2*, CHEN Hong-song1,2
    2016, 35(6):  1453-1459. 
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    The objective of this study was to apply multivariate empirical mode decomposition (MEMD) in revealing scale-specific characteristics of soil organic carbon (SOC) and total nitrogen (TN) and their main affecting factors. Using the transect method (20 m interval), 50 soil samples were collected from the peak-cluster depression. SOC and TN and environmental factors were separated into different intrinsic mode abductions (IMFs) and residues represented different scales. The multicharacteristic scales were IMF1, IMF2, IMF3 and IMF4 for SOC, and IMF1, IMF2, IMF3, IMF4 and IMF5 for TN. The dominant scales for SOC were similar with for TN. The dominant scales were IMF1 and IMF2 (scale: 68.6 and 140.9 m) for SOC, and IMF1 and IMF2 (scale: 73.2 and 141.1 m) for TN. IMF1 and IMF2 presented the main contribution to overall prediction of both SOC and TN. At each scale, SOC and TN were controlled by one or multiple factors. Significant correlations between rock ratio and SOC and TN were found both at measured scales and all IMFs. However, the relations between SOC and TN and the other environmental factors were complex. The significant correlations between SOC, TN and topographic wetness index and soil water at smaller scales (141.0 m) were strongest. The significant correlations between SOC and TN and pH at moderate scales (229.2 m) were strongest. The significant correlations between SOC and TN and elevation and slope at larger scales (362.9 m) were strongest. Our results showed that SOC and TN were controlled by different environmental factors at different specific scales. Our findings provide a better understanding of the relationships between SOC and TN and their main affecting factors at specific scales, and provide scientific basis for adaptive landscape pattern design and land-use structure adjustment.
    Effects of environmental factors on transpiration of three tree species in the Dongting Lake Basin.
    LIU Na1, GUAN Hua-de1,2, LUO Zi-dong1, ZHANG Ci-cheng1, ZHANG Xin-ping1*, WANG Ting1
    2016, 35(6):  1460-1466. 
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    Transpiration, influenced by many environmental variables, is one of the important physiological activities for plants. The responses of transpiration to environmental factors (solar radiation, vapor pressure deficit and soil water potential) were examined for some tree species (Osmanthus fragrans, Cinnamomum camphora and Liquidambar formosana) over three years with distinguished precipitation amounts (drought summer in 2013 and wet in 2014 and 2015) based on a recently developed transpiration model (the modified Jarvis-Stewart model). The model calculates transpiration from a maximum value scaled down by three functions of individual environmental factors. The functions were rigorously parameterized simultaneously using an advanced optimization algorithm. The results indicated that: (1) The transpiration response of O. fragrans and L. formosana to solar radiation was more sensitive than  C. camphora, while C. camphora transpiration was more sensitive to VPD than O. fragrans and L. formosana. (2) On average during the whole growing season, the primary impact factor of plant transpiration was water potential in 2013, and VPD in 2014 and 2015. (3) The dual impact of VPD to transpiration was observed in 2013, in which an optimal VPD for transpiration occurred. Away from this optimal VPD value, transpiration decreased. In 2014 and 2015, transpiration increased with VPD.
    Responses of leaf traits of Sassafras tsumu (Hemsl.) Hemsl. along an altitudinal gradient.
    JIANG Ai-ping, JIANG Jing-min, LIU Jun*
    2016, 35(6):  1467-1474. 
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    Leaf traits, the results of long-term interactions between plants and environment, are extremely sensitive to the surroundings in the process of evolution and influence the plants’ ‘costbenefit’ relationship. We investigated the leaf traits of Sassafras tsumu (Hemsl.) Hemsl. along an altitudinal gradient in the Tianmushan Mountain. Leaf morphological traits of S. tsumu, including leaf area, the ratio of leaf length to width, leaf dry weight and specific leaf area, were analyzed. Similarly, leaf physiological traits, including chlorophyll concentration and leaf nitrogen content (Narea), were analyzed. The results indicated that a significant difference existed in leaf area, and extremely notable differences existed in specific leaf area, the ratio of length to width and dry weight among subpopulations along the altitudinal gradient. Additionally, the coefficients of variation of dry weight and the ratio of lengthwidth within populations was less than those of leaf area and specific leaf area, which illustrated that leaf morphological traits exhibited different variations among subpopulations. Moreover, specific leaf area had significant positive correlations with leaf area and the ratio of length to width, while it had a significant negative correlation with leaf dry weight. Chlorophyll concentration showed a significant positive correlation with Narea. The linear regression relationship between the leaf characteristics and temperature demonstrated that leaf area, specific leaf area, chlorophyll concentration and Narea decreased as temperature dropped. On the contrary, dry weight and the ratio of length to width gradually increased.
    Biomass allocation pattern and its influencing factors across natural Chinese pine forests of different ages in Songshan, Beijing.
    GAO Jie, GUO Zi-jian, LIU Yan-hong*
    2016, 35(6):  1475-1480. 
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    Currently, Beijing Songshan Nature Reserve possesses the only one natural Chinese pine forest in North China. We investigated 8 different aged natural Chinese pine forests in the reserve and used RDA analysis and variance decomposition to explore the effect of environmental factors on biomass allocation pattern in organs. Results indicated that biomass of tree layer increased with the increased stand age, and the biomass values of 40, 55, 70 and 95yearold forests were 116.96, 132.31, 144.86, and 170.82 t·hm-2, respectively. The biomass of various organs (roots, leaves, bole wood, branches) also increased with the increase of stand age, but no significant difference in biomass allocation ratio of each organ existed among the forests with different ages (P>0.05). Stand age showed a significant positive linear correlation with organ biomass in tree layer. The two main components of environmental factors together accounted for 96.79%, 46.04%, and 86.80% of the variance of biomass distribution pattern in tree layer, shrub layer, and herb layer, respectively. The independent effect of the soil factor model was much greater than that of the terrain model in interpretation of the variance of tree layer and herb layer’s biomass allocation pattern, while the terrain factor model showed a greater independent role in explaining the variance of shrub biomass allocation pattern than the soil factor model.
    Community dynamics and stability of different aged Pinus massoniana plantations in southern Guangxi.
    PAN Deng, ZHANG He-ping*, PAN Gao
    2016, 35(6):  1481-1490. 
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    To explore community succession dynamics and stability change of Pinus massoniana plantation, the community structure, reproduction potential, species diversity, Godron index were determined among different successional stages (10, 18, 22, 28 and 50 a) in Laohuling in Southern Guangxi, by using a spacefortime substitution approach. The result showed that with the succession, the dominance of deciduous trees declined, but the dominance of evergreen trees increased. The reproduction potential of community increased first and decreased afterwards. The distribution of diameter size followed the unimodal type for P. massoniana, presenting a decline trend due to lack of seedlings. An ‘L’ or inverseJ type distribution was found for Lithocarpus glaber diameter size, with adequate supplement of seedlings. With the forest succession, the species richness decreased, the Simpson index and Shannon index increased first and decreased afterwards, and the Godron index increased. The relationship between Godron index and diversity index was not linear, and the species diversity could not fully represent the community stability.
    Structural regulation and natural restoration of Futian Mangrove in Shenzhen Bay.
    HU Tao1, CHOU Qing-chuan1, HE Shi-yu1, XU Hua-lin2, SHI Xiu-hua3*
    2016, 35(6):  1491-1496. 
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    A structural regulation experiment was carried out to decrease the abundance of the introduced mangrove species Sonneratia caseolaris and S. apetala in a mangrove forest in Futian Mangrove Reserve in Shenzhen Bay in May 2014. The natural restoration of mangrove plants was investigated once a month during June 2014 to May 2015. The results showed that there were five mangrove species in the testing plots, including Kandelia obovata, Aegiceras corniculatum, S. caseolaris, Avicennia marina and S. apetala. Their importance values were 36.72, 32.51, 20.96, 5.28 and 4.53, respectively. After thinning, native mangrove plants played a more important role in the natural recovery process, whereas introduced mangrove S. caseolaris grew faster, competing with the native mangrove species. In order to improve the competitive ability of native mangrove species, multiple artificial regulations for S. caseolaris are needed in the future. The species richness within the testing plots was high, but the individuals of each species distributed unevenly. Therefore, supplementary planting of native mangrove species is needed in the future to ensure the stability of mangrove community structure.
    Tradeoff relationship between the flower biomass and number of Zygophyllum xanthoxylum on different slope aspects in northern slope of Qilian Mountains.
    HAN Ling, ZHAO Cheng-zhang*, XU Ting, DUAN Bei-bei, ZHENG Hui-ling, FENG Wei
    2016, 35(6):  1497-1503. 
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    Tradeoff is the basis of the theory on plant life-history strategies, and the trade-off between flower size and flower number is an important determinant of flower biomass allocation. In this study, GIS and the method of experimental ecology were used to study the relationship between flower size and number of Zygophyllum xanthoxylum in response to slope aspects located in desert grasslands on the northern slope of Qilian Mountains, Northwest China. The results showed that the height, density, aboveground biomass, soil moisture content of the plant community and flower size, twig number, dry weight of Z. xanthoxylum displayed a pattern of gradual decrease with the aspect turning from north, east, west to south, while the flower number and reproductive allocation of Z. xanthoxylum displayed a pattern of gradual increase. The flower size was highly significantly negatively correlated with flower number on the north slope and south slope (P<0.01), and the slopes of the regressions were significantly less than -1, whereas it was significantly negatively correlated with flower number on the east slope and west slope (P<0.05), and the slopes of the regressions were close to -1. The trade-off relationship of resource allocation between the flower size and flower number of Z. xanthoxylum in different slope aspects reflected the population reproduction strategy via optimizing habitat adaptability of plant.
    Effects of interspecific competition on the growth of invasive and native species.
    ZHOU Yu-lu, LI Ling-yun, GAO Jun-qin*, DING Yan
    2016, 35(6):  1504-1510. 
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    To explore interspecific relationship between invasive and native plants, we conducted a greenhouse experiment with two invasive plants (Alternanthera philoxeroides and Wedelia trilobata) and their native congeners (A. sessilis and W. chinensis) across monoculture and mixture plantings. Biomass and morphological indexes were measured and the interspecific relationships between species were analyzed. The results showed that: (1) Congener and heterogeneric interspecific relationship increased the biomass, root/shoot ratio and number of nodes of A. philoxeroides, but decreased the height and number of nodes of W. trilobata. (2) Congener interspecific relationship decreased the height of A. sessilis and number of nodes of W. chinensis, heterogeneric interspecific relationship increased the biomass, height and number of branches of A. sessilis, but decreased the total biomass and height of W. chinensis. (3) Congener interspecific competition had a positive effect on the growth of A. philoxeroides, while heterogeneric interspecific competition had a positive effect on the growth of A. sessilis. In future studies, relationships of cooperation and competition between invasive and native plants in the field need to be advanced to provide a theoretical basis for prevention and control of invasive plants.
    The impact of propagule pressure on the successful colonization and population persistence of invasive weed Ambrosia artemisiifolia. #br#
    DENG Zhen-zhen1,2, ZHAO Xiang-jian1, ZHAO Cai-yun1, LI Jun-sheng1*
    2016, 35(6):  1511-1515. 
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    Common ragweed (Ambrosia artemisiifolia) seeds were collected from Mentougou District, Beijing, China, and a field experiment was conducted in a fallow field in Shunyi District, Beijing, China, during 2013-2014. In order to evaluate the effect of propagule pressure on common ragweed’s recruitment, colonization and population persistence, four levels of common ragweed seeds (5, 10, 20 and 40 seeds·m-2) were sown in 12 plots. The results showed that there was a positive correlation between propagule pressure and the proportion of plots with common ragweed successfully recruited and colonized in both 2013 and 2014. When the propagule pressure reached or were more than 20 seeds·m-2, the population of common ragweed could be successfully established and even continued to expand next year. The number of common ragweed recruited and colonized in the plots in the second year was significantly higher than in the first year (P<0.05). The plots that had 1-3 seedlings successfully colonized in 2013 were able to maintain their population in 2014, in which the number of seedlings recruited in 2014 ranged from 5 to 237, and only 4 to 97 adult plants were successfully colonized at the end of the experiment. Results indicate that low propagule pressure of common ragweed can likely cause invasion, and the probability of successful colonization increased with propagule pressure; only a few plants of common ragweed may produce enough seeds for population persistence and expansion. As a result, it is necessary to strengthen the quarantine of common ragweed seeds and eliminate the few plants occurred in new distribution area in time.
    #br# Spatial and temporal variations of hydrochemical compositions of river water in Qinhe Basin.
    QIN Yong1, ZHANG Dong1,2*, ZHAO Zhi-qi2
    2016, 35(6):  1516-1524. 
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    Qinhe Basin, a small watershed in North China, was chosen, and spatial and temporal variations of chemical composition in river water were described to illustrate the controlling roles of natural factors and anthropogenic activities on the base of two sampling campaigns during flood and normal seasons for mainstream and tributaries combined with onsite determination and indoor analysis. The results indicated that: (1) Cations were dominated by Ca2+ and Mg2+ in river water samples of Qinhe Basin during the two seasons accounting for 45% and 41% of total cations in terms of equivalent values during flood season and 43% and 41% during normal water season, respectively. Anions were dominated by HCO3- and SO42- in river water samples and their ratios of equivalent values were 46% and 39% for flood season and 55% and 27% for normal season, respectively. The water type was mainly HCO3--SO42--Ca2+-Mg2+. (2) The average values of δD and δ18O were -65.4‰ and -8.76‰ in flood season and -64.6‰ and -8.68‰ in normal season respectively. Atmospheric deposition was the main recharge sources for river waters in Qinhe and some of them with positive hydrogen and oxygen isotope values experienced evaporation. (3) The ratios of SO42- and HCO3- in terms of equivalent values were 0.96 and 0.54 during flood and normal season respectively, and the ratios between Ca2++Mg2+ and HCO3- equivalent values were 1.88 and 1.78 in flood and normal season respectively. The sulfuric acid derived from acid rain and oxidation of sulfide minerals had participated in chemical weathering process of carbonate minerals. (4) Nitrate and total mercury concentrations of river waters gradually increased downstream, which indicated the influences from anthropogenic activities mainly including sewage water, industrial waste water and agricultural activities.
    Effect of different forms of sulfur on Hg content in Bruguiera gymnorrhiza seedlings.
    YUAN Jun, ZHANG Ling, JIN Ming-hua, DING Zhen-hua*
    2016, 35(6):  1525-1530. 
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    Sulfur (S) plays a key role in Hg biogeochemical cycle. To understand the effect of S in different chemical forms (S, Na2SO4, Na2S) on absorption of Hg in mangrove plants, a pot experiment was conducted with Bruguiera gymnorrhiza (L.) Lamk seedlings treated with different chemical forms of S (S, Na2SO4, Na2S) at different concentrations (0, 0.1% S, 1% S). The potting soil was taken from a farmland with Hg pollution. Sulfur (S0), sodium sulfate (Na2SO4), or sodium sulfide (Na2S) was added in the soil. Contents of total mercury (THg), methylmercury (MeHg) and sulfur in different organs of B. gymnorrhiza were determined. The results showed that Hg absorption in stem increased under stress of the three different sulfur compounds, while the situation in root and leaf was more complicated and irregular. Sulfur’s chemical forms predominantly affected the MeHg content in the root, and sulfuradding enhanced MeHg concentration in root. There was a significant positive correlation among contents of sulfur, Hg, and MeHg in the roots (P<0.01). On the contrary, the correlation between sulfur content and mercury content in aerial parts of stems and leaves was not significant (P>0.05).
    Geochemical distribution and environment risk of heavy metals in urban soil of Xining City.
    YANG Rui, LI Xiao-ping*, WANG Ji-wen, XU Qiang, YANG Tao
    2016, 35(6):  1531-1538. 
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    A total of 155 soil samples in the four regions (the west, the central, the east and the north) of Xining City were collected according to the random sampling method. The concentrations of heavy metals, As, Cr, Co, Cu, Pb, Sr and Zn were measured using the method of Xray fluorescence spectroscopy (XRF), and their potential ecological risk and health risk were evaluated. The results showed that the concentrations of heavy metals in this study were beyond the soil background values except As and Zn. The potential ecological risk index of the heavy metals in Xining City was moderate. The potential ecological risk was in order of Cr>As>Pb>Co>Sr>Cu>Zn. Among the four regions, the potential ecological risk level decreased as the north (39.7) > the central (33.3) > the east (31.5) > the west (30.6). According to the health risk index, hand to mouth contact was still the main pathway to posing human risk, and the heavy metals had a higher noncarcinogenic risk to children than to adults in any exposure pathway. The total noncarcinogenic risk to children in the four regions declined as the north > the central > the east > the west. Heavy metal Cr had the highest noncarcinogenic risk in all of the regions, especially in the north area, with high HI index exceeding the safety threshold value 1. Meanwhile, the order of carcinogenic risk index was the north > the east > the central > the west. In the north area, the carcinogenic risk index of Cr ranged from 10-6-10-4, which would pose possible carcinogenic risk to humans. Therefore, attention should be paid and the relevant measures should be taken.
    Isolation of heavy PAH-degrading bacteria and their characteristics of degradation.
    GAO Ye-meng1, YANG Xue-lian1*, LI Feng-mei2, WANG Sa3, TENG Fei1, WANG Wu1, SHENG Yuan-yu1
    2016, 35(6):  1539-1546. 
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    Seven PAH-degrading strains were isolated from PAHs-contaminated soil around an iron and steel company in Benxi using the enrichment procedure and tablet sublimation method. Their degradation ability of PAHs was studied in flasks with pyrene or benzo\[a\]pyrene as the single carbon source. The results showed that G1, G2 and G3 strains had stronger degradation ability for heavy PAHs. Further studies on the degradation ability of G1, G2, G3 and their mixture in PAHscontaminated soil indicated that at 80 days, the total PAH-degradation rates in the four treatments were in order of the mixture > G2 > G1 > G3. Compared to the treatments that inoculated with G1, G2 and G3 alone, the degradation rate in the treatment inoculated with the mixture was enhanced by 9.17%, 11.49%, and 16.11%, respectively. Compared with the control treatment, the degradation rates of 4-6-ring PAHs increased in the four treatments and the times of their increase were enhanced with the number of rings. Meanwhile, there was a positive correlation between the dehydrogenase activity and PAHs degradation. The degradation rates of 4-, 5-, and 6-ring PAHs were enhanced by 12.13%, 13.35%, and 14.52% in BioEK experiment than in the Bio experiment, which indicated that G1, G2 and G3 have good ability of adapting to electric field. G1, G2 and G3 strains were identified as Sphingomonas sp., Ochrobactrum sp. and Achromobacter sp. respectively based on their physiological characteristics and the sequence analysis of 16S rRNA.
    Response of bacterial community in PAHs contaminated soil during physically enhanced remediation.
    SONG Yu1, WANG Jian2,3, SU Zhen-cheng2*, ZHANG Hui-wen2
    2016, 35(6):  1547-1552. 
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    Responses of bacterial community in polycyclic aromatic hydrocarbon (PAHs) contaminated soil remedied by reversal electric field were assessed by denaturing gradient gel electrophoresis (DGGE) and realtime quantitative PCR. The results showed that reversal electric field was favorable to the degradation of PAHs. The degradation rates of PAHs in the soils near the electrode and at electric field center were both more than 50%, especially in the soils at electric field center. During the remediation, bacteria 16S rRNA gene copy numbers and diversity indices of bacterial communities had no significant change between the soils near the electrode and at electric field center, and also showed no significant difference compared with the control. However, bacterial community structure showed obvious difference between the soils near the electrode and at electric field center, and had greater change compared with the control. The results suggested that changes in composition of bacterial community after application of electric field might be one of microbiological mechanisms of electro-enhanced bioremediation.
    Habitat selection by Naemorhedus goral during summer and winter in the Zhouzhi Nature Reserve of Qinling Mountain.
    BIAN Kun1, WANG Kai-feng1*, LIU Chu-guang1, SI Kai-chuang2, ZHU Dai-bo2, WANG Zhi-jun2
    2016, 35(6):  1553-1560. 
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    Goral habitat selection was observed and analyzed in this study using belttransect methods at Zhouzhi Nature Reserve in Shaanxi Province in winter (February 2014 and December 2014 to January 2015) and summer (June 2015 to July 2015). We established 23 belt transects to collect goral habitat selection information. In summer, goral preferred areas with the following attributes: conifer forest, grassland and gravel, high altitude (>1900 m), upper slope position, high slope gradient (>20°) and sunny slope, short tree dispersion (<4 m), big tree size (>60 cm), tall shrub (>1.2 m), 30%-45% shrub overage, high herbage overage (>40%), short distance to hides (<5 m), moderate hiding cover (>30%), and long distance to human disturbance (>1 km). In winter, goral preferred areas with the following attributes: broadleaf forest, moderate altitude (1500-1900 m), lower slope position, 10°-20° slope gradient and sunny slope, low canopy (<20%), moderate tree dispersion (<6 m), tall shrub (>1.2 m), low shrub density (<5 trees·20 m-2), 1-2 m shrub dispersion, 15%-30% shrub overage, moderate herbage overage (>20%), 5 or more herbage species, moderate hiding cover (>30%), short distance to water sources (<1 km) and short distance to human disturbance (<1 km). Binary Logistic regression results showed that eight factors controlled goral habitat selection in summer: slope direction, slope position, tree size, tree dispersion, shrub size, hiding cover, distance to hides, and distance to human disturbance. In winter, nine factors controlled the habitat selection: slope direction, slope position, canopy, tree dispersion, shrub size, shrub dispersion, herbage species, hiding cover, and distance to water sources.
    Age structure and growth characteristics of exotic fish Clarias gariepinus (Burchell, 1822) in south China.
    ZHU Yun-jie1,2, GU Dang-en1, WEI Hui1, MU Xi-dong1, LUO Du1, XU Meng1, LUO Jian-ren1, HU Yin-chang1*
    2016, 35(6):  1561-1568. 
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    To determine the age structure and growth characteristics of Clarias gariepinus, sagitta ray sections, body length and weight were examined using 223 specimens collected in South China during August 2011 and June 2015. These specimens were comprised of 3 age groups ranging from age 1 to age 3. Additionally, the dominated age was age 1, accounting for 60.19% of the total specimens. The formulas of the relationship between standard body length (L) and total weight (W) for females and males were W=5.763×10-5 L2.737 (n=87, R2=0.989),W=9.239×10-5L2.631 (n=122, R2=0.942), respectively, which showed that the growth of C. gariepinus was nearly isometric. The growth pattern of C. gariepinus was formulated by Von Bertalanffy growth function as follow: Lt=455.566(1-1877.112e-8.036t), Wt=1089.19(1-1877.112e-8.036t)2.737 for females and Lt=475.187(1-1.48e-0.908t), Wt=1019.66(1-1.48e-0.908t2.631  for males. The growth inflection points for females and males were 1.07 and 1.64 respectively when the corresponding standard body lengths on the growth infection points were 297.75 mm for females and 316.79 mm for males, and the corresponding total weights were 340.08 g for females and 350.88 g for males. Analysis also showed that the growth rate became lower with the increasing age, and the younger matured individuals grow faster than the older ones. Our results suggested that C. gariepinus has a large population size with single age structure in South China. Moreover, C. gariepinus population is in the rapid growth period, and is likely to burst into a sudden growth in the South China.
    Characteristics of fish assemblages associated with environmental factors in the Lake Erhai. 
    ZHOU Xing-an1, QIAO Yong-min1,2, WANG sai1, YANG yang1,2*, LIU Xi-xi1
    2016, 35(6):  1569-1577. 
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    An investigation of fish species composition and assemblage structure was conducted in the Lake Erhai from 2014 to 2015, and the environmental factors were determined at the same time. 24 species of fish belonging to 6 orders, 11 families and 21 genera were collected, including 19 exotic species and 5 native species. There were 13 species from Cyprinidae and 2 species from Gobiidae, which accounted for 54.2% and 8.3% of the total species, respectively, with only one species in each of the remaining 9 families. The spatial distribution of fish assemblages consisted of two major types: species living in pelagic zones and those in littoral zones. The fish density and biomass in both pelagic zones and littoral zones were higher in May and July than those in January and September. Compared with littoral zones, both the density and biomass in pelagic zones were much higher. Notably, the structure of fish assemblages was found to be miniaturized and simplified. As revealed by the index of relative importance (IRI), five dominant species were Neosalanx taihuensis, Hemiculter leucisculus, Hypophthalmichthys molitrix, Carp cyprinus and Carassius auratus. Three diversity indexes showed low assemblage diversity throughout the year; the spatial distribution of Shannon index (H) and Pielou’s evenness index (J) had a trend similar to that of fish density and biomass. The spatial differences in fish density and biomass as well as assemblage diversity were significant (P<0.05), but the seasonal differences were not significant (P>0.05). Furthermore, water depth, dissolved oxygen and eutrophication were the main environmental factors affecting the spatiotemporal distribution of fish assemblages.
    Macrobrachium nipponense can recognize predation through the alarm cues released by conspecifics.
    BU Rong-ping, JIANG Ni, XIE Hai, WU Zheng-jun
    2016, 35(6):  1578-1582. 
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    Many aquatic animals can release alarm cues to transmit warning when stressed by a predator. Recognizing the cues released from their conspecifics, aquatic animals will response with antipredation appropriately. Macrobrachium nipponense is a key and one of the most promising aquaculture species in China. Whether they can recognize their predator is important for their survival. In the present study, we used M. nipponense as a model species to explore whether it can recognize the alarm cues released by their conspecifics which have visually recognized by their shared alien predator Procambarus clarkii. Our results indicated that the number of M. nipponense (3.20±0.94,n=80) (mean±SD) in the experimental group trying to hide under the shelter was significantly higher than that in the control group (2.81±0.80,n=80) (repeated measures ANOVA: F1,156=7.753, P=0.006). In the initial stage, the number of M. nipponense (28.90±21.19,n=40) crossing the midline in the experimental group was significantly lower than that of the control group (69.08±21.58,n=40) (Wilcoxon signed ranks test: Z=-5.498, P<0.01). In the final stage, the number of M. nipponense (19.93±12.44,n=40) crossing the midline in the experimental group was significantly lower than that of the control group (36.33±21.17,n=40) (paired ttests: t39=6.618, P<0.01). The results suggest that M. nipponense can detect alien predator cues released by their conspecifics, and have antipredation behaviors by increasing the usage of shelter and decreasing their activity level. We predict that M. nipponense will therefore increase its vigilance to predators and survival by recognizing its congener’s chemical cues.
    Swimming performance of juvenile Aristichthys nobilis under fixed velocity swimming tests.
    HOU Yi-qun1, NEWBOLD Lynda2, CAI Lu1, WANG Xiang1,3, HU Wang-bin1, QIAO Ye1*
    2016, 35(6):  1583-1588. 
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    Bighead carp (Aristichthys nobilis) is an important commercial fish in China. Sustained and prolonged swimming speeds are two important parameters to assess the swimming performance of the fish. In this study, one hundred and eighteen juvenile bighead carp were divided into three groups according to total length (TL): 12.5-17.5, 17.5-22.5 and 22.5-27.5 cm. Fixed velocity tests were used to measure sustained and prolonged swimming speeds in an open channel flume. Sustained swimming speeds for the three groups were 13.7-39.8, 46.1-78.0 and 60.3-75.7 cm·s-1, and prolonged swimming speeds were 29.9-60.0, 65.3-120.2 and 59.2-122.9 cm·s-1, respectively. Nearly all (>98%) of the fatigue time was in one of two ranges: either <10 min or >200 min. Both sustained swimming speed (Us) and prolonged swimming speed (Up) increased as a linear function of water temperature (T) from 18 ℃ to 26.3 ℃. The correlations were significant if absolute speeds were converted to relative speeds (U/TL, TL is the total length): Us=0.19T-1.57 (n=27, R2=0.48, P<0.001); Up=0.20T-0.63 (n=83, R2=0.22, P<0.001). The results indicate that the time interval needs to exceed 10 min in the critical swimming speed (Ucrit) test, and the penultimate velocity before fatigue can be considered the maximum sustainable speed. Temperature also significantly affected the sustained and prolonged swimming speeds, displaying the same trend as Ucrit in the optimal temperature range.
    Effects of mussel (Anodonta woodiana), submerged macrophyte (Vallisneria natans) and their coexistence on water quality.
    LI Ping, ZHANG Xiu-feng*, MO Shu-qing
    2016, 35(6):  1589-1594. 
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    Filter-feeding mussel and submerged macrophyte are important components of aquatic ecosystem, playing a key role in determining the structure, function and process of shallow lakes; however, the effects of their coexistence on water environment in shallow lakes are still unclear. Mesocosm experiments (control, mussel treatment, submerged macrophyte treatment, and coexistence of mussel and submerged macrophyte treatment) were conducted to evaluate the effects of filterfeeding mussel Anodonta woodiana, submerged macrophyte Vallisneria natans, and their coexistence on water quality. Results showed that the mussel reduced the growth of phytoplankton measured as Chl-a (P<0.05). The submerged macrophyte decreased the concentrations of total nitrogen (TN), nitrate (NO3--N), total phosphorus (TP), total dissolved phosphorus (TDP) and Chl-a (P<0.05). Coexistence of the mussel and macrophyte decreased both nutrients and Chl-a (P<0.05), meanwhile existence of the mussel promoted growth of the macrophyte. Dry -biomass- and height of the macrophyte in mesocosm were higher with coexistence of the mussel and macrophyte than those of the macrophyte alone at the end of experiment (P<0.05).
    Effects of wind wave on distribution pattern of Sargassum horneri around Gouqi Island.
    BI Yuan-xin, WANG Wei-ding*
    2016, 35(6):  1595-1600. 
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    The distribution of Sargassum horneri around Gouqi Island was investigated by diving in May 2015. Typhoon data over the last 65 years in the northwestern Pacific and wind data over the last 3 years around Gouqi Island were collected, and the effect of wind wave on the distribution of S. horneri was analyzed. The results showed that S. horneri was abundant in northwestern coast, especially at 1 to 4 m water depth, while no S. horneri was observed in eastern and southern coasts, presumably due to wind wave caused by 85.1% typhoon. Recently the abundance of S. horneri around Gouqi Island decreased, but there was no evidence to deduce this change resulting from the increased typhoon frequency. North and northwest winds were strong and occurred more often around Gouqi Island, yet S. horneri gathered in the northwestern coast, probably because of the large amount of mussel culture rafts which might relieve the negative impact of wind wave and protect S. horneri. In conclusion, wind wave had an important effect on the distribution of S. horneri around Gouqi Island.
    The maximum snow depth, snow pressure, and critical indicators of sunlight greenhouse collapsing in Northeast China.
    ZHANG Shu-jie1*, CHEN Yan-qiu2, WANG Ping3, HAN Xiu-jun2, MA Shu-qing4, WU Man-li2, LI Guang-xia2, LIU Qing-wu1
    2016, 35(6):  1601-1607. 
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    The design and construction of sunlight greenhouse need to balance the stability and cost, which are mainly affected by the snow load (the maximum snow depth and snow pressure). In this paper, based on the observation data of snow depth collected from 179 weather stations from 1981 to 2010, the maximum snow depth and pressure for recurrence intervals of 5, 10, 20 and 30 years in Northeast China were calculated using the extreme value type I distribution function, and their distribution characteristics were analyzed. The maximum sustainable snow depth and snow pressure were determined based on the type of sunlight greenhouse structure and the characteristics of snowproof coverings. The critical indexes of snow pressure and snow depth for sunlight greenhouse collapsing were concluded. The results showed that the maximum snow depth and snow pressure increased from west to east in Northeast China. The maximum snow depth and snow pressure were higher in the eastern and northern Heilongjiang and eastern Jilin, being over 50 cm and 0.45 kN·m-2, respectively. The maximum snow depth and snow pressure were low in the southwestern Heilongjiang, western Jilin, and western and southern Liaoning, with values of less than 30 cm and 0.25 kN·m-2, respectively. Snowinduced disaster index for sunlight greenhouse varied depending on snow type and slope of greenhouse, and the snow depth that induced sunlight greenhouse collapsing was bigger for pure snow than for snowwater mixture. The snow depth of blizzard disaster increased with the slope angle of sunlight greenhouse increased from 30 to 40 degree. It could be concluded that south and west areas of Northeast China are more suitable for the development of sunlight greenhouse than north and east areas based on disaster index, snow depth and snow pressure, and light and heat conditions.
    Analysis of the temporal and spatial pattern of the green infrastructure network in Nanjing, based on MSPA.
    YU Ya-ping1, YIN Hai-wei1*, KONG Fan-hua2, WANG Jing-jing1, XU Wen-bin1
    2016, 35(6):  1608-1616. 
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    We analyzed the temporal and spatial patterns of the land use types in Nanjing using TM/ETM remote sensing image data from 1988, 2000 and 2013. Then, using the morphological spatial pattern analysis (MSPA) method, we obtained the landscape types of the green infrastructure (GI) for each of the three periods, and quantitatively analyzed its spatial and temporal patterns of changes. Finally, changes in the landscape connectivity of the core area were quantitatively evaluated using landscape connectivity index and landscape graph theory. The results show that, from 1988 to 2013, the total area of GI in the study area had a slower rate of increase, showing that the implementation of a series of “green Nanjing” strategic project had obtained certain achievements. From 1988 to 2013, core area and edge area increased, but the bridge zone, branch continued to decrease, loop zone overall decreased, indicating the increase in the degree of urban landscape fragmentation and the decrease of landscape connectivity. The analysis of GI network based on the landscape connectivity index showed that both of the integral index of connectivity and the probability of connectivity decreased at first and then increased; the level of GI network connectivity which was based on graph theory increased at first and then decreased. Generally speaking, the level of connectivity of GI in the study area was still relatively low. The case analysis of Nanjing GI network pattern results showed that the research which combined MSPA with landscape connectivity and graphic theory provided a new framework for the green infrastructure pattern change analysis. These results can serve as a reference for green infrastructure network planning and optimization in the study area, as well as important guidance for other regions.
    Modeling the onset of greenness of different types of vegetation and its variation characteristics.
    WU Rong-jun1,2*, LU Yi1
    2016, 35(6):  1617-1626. 
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    The onset of greenness of vegetation is one of the important parameters to investigate the relationship between growth periodicity of vegetation and climate change. This study selected three areas including Tibetan Plateau, mideastern and northeast of China as typical research areas. Based on the cumulative frequency data of NDVI on NOAA/AVHRR in 1983—2012, Logistic fitting functional model was used to calculate the DOY (days of year) of onset of greenness with MODIS Collection 5 landcover data. The characteristics and differences of the onset of greenness with different vegetations in different areas were analyzed. The results showed that the onset of greenness by different vegetations of grasslands, shrub, deciduous tree and cropland generally presented a trend in advance. The different types of vegetation had different onsets of greenness in the same area. The interannual variability of the onset of greenness by the same vegetation types showed different trends in the different areas. The onset of greenness of grassland in the Tibetan Plateau changed at a rate of 6.11 d·10 a-1 in advance, 5.37 d·10 a-1 in the mideastern regions in China, and 2.13 d·10 a-1 in the northeast of China. The amplitude of interannual change of deciduous trees was roughly similar to that of the grassland. The changing rate of onset of greenness in advance would gradually be smaller with the increase of latitude and the decrease of altitude. The onset of greenness of the vegetation types of shrubs and cropland in northeast China appeared a delaying trend, with respective delaying rates of 1.49 and 1.03 d·10 a-1.
    Modeled impact of cropland expansion on regional climate in India.
    MAO Hui-qin1, XIONG Zhe2*, YAN Xiao-dong3, ZHANG Li-juan1
    2016, 35(6):  1627-1634. 
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    With the second highest percentage of farmland in the world, India was selected as the simulation experiment region to determine the impact and the mechanism of cropland expansion on regional climate. Based on global potential vegetation datasets and cropland dataset of HYDE V3, simulation experiments were conducted by using the Regional Integrated Environmental Model System (RIEMS) version 2.0 over potential vegetation and rainfed cropland areas of India. The results showed that, at the national scale, over the 10-year time period, the annual averaged air temperature increased by 0.1 ℃ and the precipitation rate decreased by 0.1 mm·d-1 (12.8%). The climatic effect of cropland expansion varied in different climatic zones and different seasons in India. The temperature increased by 0.5-1.0 ℃ in subtropical humid region, 0.3-0.5 ℃ in semiarid and arid region, and decreased in tropical wet and dry region. The temperature increased by 0.2 ℃ in winter and 0.5 ℃ in pre-monsoon season and decreased by 0.5 ℃ in postmonsoon season, and there was no notable change in monsoon season. The subtropical humid region, semiarid and arid regions saw the notable decreased precipitation, and dry season saw the decreased precipitation, with the largest of 0.3 mm·d-1 in the premonsoon season. The increased sensible heat flux, the decreased latent heat flux and the downward flow due to the divergence circulation at 850 hPa resulting from the rainfed cropland expansion can give the reasonable explanation for the increased temperature and decreased precipitation.
    Modeling the effect of natural ventilation on temperature inside solar greenhouse.
    SU Wen1, XUE Xiao-ping2*, XIONG Yu1, CAO Jie2
    2016, 35(6):  1635-1642. 
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    The 3-D numerical simulation was utilized to study temperature distribution of the greenhouse under natural ventilation in winter based on the experimental observation of the solar greenhouse with tomatoes in Jinan. The temperature distribution was obtained using the computational fluid dynamics (CFD) numerical techniques with the support of the standard κε turbulent model and the discrete ordinates (DO) radiation model. The results showed that the CFD numerical techniques could generate a satisfactory simulation of the temperature variation of the naturally ventilated solar greenhouse. The average error between the simulated and actual temperature was 0.9 ℃. In the sunny days in winter, the temperature of the greenhouse could reach the suitable level for crop within 16-23 min under the conditions of the different wind directions and the corresponding average wind speeds in Jinan. The temperature difference was around 3 ℃ between the temperatures in the north and south and around 4 ℃ between the east and west when the wind direction was NE, ENE, E, ESE, SE, SW. The temperature difference was around 4 ℃ between the north and south and around 1 ℃ between the east and west when the wind direction was SSW. Our results could provide a scientific reference to the structural optimization and the production management of the solar greenhouse.
    Effect of canopy layers on the accuracy of net ecosystem productivity simulation: A case study on temperate mixed broadleaf-conifer forest ecosystem of Changbai Mountain.
    QIAO Yan-yan1, REN Chuan-you1, WANG Yan-hua1*, YANG Ya-li1, WANG Guan2, SHANG Ying1, CHEN Mei-juan1
    2016, 35(6):  1643-1652. 
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    Based on meteorological gradient observation data during 2003-2008, the net ecosystem productivity (NEP) was simulated using multi-layer model under different canopy layered numbers of mixed broadleaf-conifer forest of Changbai Mountain. By comparing the modeled NEP with those measured by eddy covariance system, the influence of different layered numbers on simulated NEP accuracy was analyzed with the criteria of the maximum coefficient of the determination (R2) and the minimum rootmeansquare error (RMSE). The results showed that: (1) The model built in this study had good reappearance ability of diurnal NEP variation under different canopy layered numbers, but showing a tendency to undervaluing NEP when the layered number was small and a tendency to overestimating NEP when the layered number was large. (2) The ability to simulate diurnal variation of NEP increased with the increase of layered number when the layered number was small, while the ability to simulate diurnal variation of NEP was relatively stable with the increase of layered number when the layered number exceeded by a certain value. (3) It was advisable to divide the canopy into 4-7 layers when NEP was estimated by multilayer model at mixed broadleaf-conifer forest ecosystem of Changbai Mountain. The results can provide reference for the study of the NEP simulation of forest ecosystem.
    Influence of iron oxides on microbial methanogenesis and related mechanisms.
    TANG Zi-yang1,2, TANG Jia2, ZHUANG Li2, MA Jin-lian2, ZHOU Shun-gui2, FAN Ting1*
    2016, 35(6):  1653-1660. 
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    Methane is one of the most important greenhouse gases and clean energy sources. With the highest abundance of active metals on Earth, iron oxides exert significant influences on the conversion of organic matter to methane under anaerobic conditions. Low-crystallinity, easily reducible Fe(III) oxides could inhibit methanogenesis in three ways: (1) Fe(III)reducing bacteria competed with methanogens for common electron donors such as acetate and H2; (2) methanogens reduced Fe(III) oxides with H2 oxidation, diverting the electron flow from methanogenesis to Fe(III) reduction; (3) Fe(III) oxides might increase the redox potential of their surrounding environments to inhibit methanogenesis. Recently, the conductive iron oxides have been demonstrated to facilitate methanogenesis from organic matter, in which iron oxides function as electron conduits and create direct interspecies electron transfer between syntrophic bacteria and methanogens. This review summarizes the mechanisms of inhibition or promotion effect of iron oxides on syntrophic methanogenesis. Furthermore, we highlight the research trends of the influence of iron oxides on methanogenesis, which would be helpful for the practical applications in greenhouse gases mitigation and bioenergy production.
    Soluble organic nitrogen in soil: A review.
    ZHANG Ya-ya1,2, LI Jun1*, GUO Ying1,2, NIU Ying-quan1,2, WANG Yi-han1,2, ZHOU Wen-wen1,2
    2016, 35(6):  1661-1669. 
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    Soluble organic nitrogen (SON) plays a significant role in nitrogen cycle and nutrient balance of terrestrial ecosystems, and is one of the most active constituents of soil nitrogen. SON can not only be transformed into mineral nitrogen through mineralization, but also be absorbed directly by plants. Meanwhile, SON loss may cause eutrophication in aquatic ecosystems, and aggravation of N2O emissions in soil ecosystems as well. Therefore, SON has aroused multidisciplinary attention. In order to provide a reference for studying plant uptake and utilization of nitrogen as well as nitrogen cycle in ecosystems, this paper reviewed advances in SON sources, components, extraction, determination, ecological functions, and environmental effects of its loss. In addition, some prospects for further study on SON in soil were also proposed.
    Research advances in mechanisms of watermelon continuous cropping diseases and its biological control.
    HUANG Chun-yan1, BU Yuan-qing2, SHAN Zheng-jun2, DAI Chuan-chao1*
    2016, 35(6):  1670-1676. 
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    Fusarium oxysporum f. sp. niveum, a causal agent of fusarium wilt of watermelon, is a common soilborne pathogen that can decrease the watermelon yield and quality. It denotes one of the major factors limiting current watermelon production. In recent years, many researches have been done on it, including the symptom, occurring conditions, disease cycle and major prevention measures. In actual production, the most commonlyutilized control method is grafting. However, it is difficult to widely apply and popularize the grafted watermelon cultivation method in China. Moreover, the molecular mechanism of watermelon wilt caused by F. oxysporum f. sp. niveum remains unclear. At present, both the ecological and economic problems caused by continuous cropping obstacles of watermelon, such as the weakened regenerative capacity, soil microflora imbalances, soil fertility decline and increased rates of plant diseases, are attracting more attentions from scholars. In this review, the infection and colonization of F. oxysporum, the effects of F. oxysporium toxin on watermelon growth as well as the effects of continuous cropping of watermelon on soil ecosystems are explored. Furthermore, we summarize the underlying mechanism of watermelon continuous cropping obstacles caused by F. oxysporum. Meanwhile, the biological control methods of watermelon fusarium wilt are expounded.