Chen Xinsheng

Characteristics of soil seed bank and its relationship with aboveground vegetation in Lake Dongting

The size,composition,vertical distribution and species diversity of seed bank as well as its relationship with aboveground vegetation were studied in three dominant plant communities(Miscanthus sacchariflorus,Carex sp.,and Phalaris arundinacea) distributing with different water levels in Lake Dongting.The density of seed bank was highest in M.sacchariflorus(44656 seeds/m2),followed by P.arundinacea(31725 seeds/m2) and lowest in Carex sp.(15146 seeds/m2).Seeds in the seed bank distributed mainly within 0～5cm soil layer and decreased rapidly along with the soil depth.The seed banks of the three communities were composed of 53 species belonging to 18 families,39 genera.Among them,20 species were perennial while 33 were annual or biannual.The proportions of perennial species were 29.9%,35.2% and 38.0% in the soil seed bank of M.sacchariflorus,C.sp.and P.arundinacea communities,respectively.The diversity indexes of seed bank and aboveground vegetation were 0.76 and 0.53 in M.sacchariflorus,0.70 and 0.17 in C.sp.,0.72 and 0.45 in P.arundinacea,respectively.The similarity indexes between seed bank and aboveground vegetation were 0.28 in C.sp.,0.40 in M.sacchariflorus and 0.52 in P.arundinacea,respectively.The diversity index of seed bank was higher than that of aboveground vegetation and the similarity was relatively low.Therefore,perennial aboveground vegetation has limited contribution to the soil seed bank in large Yangtze-connected lake wetlands,where seeds might be mainly imported into seed bank through other pathways,such as water flow.

The effects of burning disturbance on the soil chemical properties of Miscanthus sacchariflorus( Poaceae ) and Carex brevicuspis( Cyperaceae ) communities at Lake Dongting wetlands

火烧作为调控因子, 对植物群落结构和生态系统功能具有重要影响, 但在湖泊湿地中研究较少.通过野外调查取样与实验室分析, 探讨火烧对洞庭湖湿地主要群落类型--荻(Miscanthus sacchariflorus)和苔草(Carex brevicuspis)土壤化学性质的影响.结果表明:火烧后, 苔草群落土壤硝态氮含量显著减少64.6%, 有机质含量增加26.3%;而荻群落土壤与之相反, 硝态氮含量增加186.9%, 有机质含量减少22.9%.火烧后, 苔草群落的全氮、铵态氮、全碳和全磷含量均显著增加, 分别增加了75.4%、36.3%、102.7%和76.9%, 而荻群落土壤与对照组间无显著差异.总体上, 火烧对荻群落土壤养分影响不大, 可作为芦苇场的一种管理方式, 但火烧促进苔草群落土壤养分释放, 有助于苔草群落提前萌芽和生长, 并引起牲畜牧食增加.

Population distribution patterns and growing status of Triarrhena lutarioriparia along a gentle elevation gradient of Lake Dongting wetlands

通过野外不同水位高程固定样地多次调查，结合方差/均值比率法研究了不同水位高程下洞庭湖湿地南荻（Triarrhena lutarioriparia）种群分布格局及生长动态.结果表明：（1）低程区土壤含水量显著高于高程区；低程区土壤颗粒组成与高程区相比有显著差异，低程区土壤为黏砂壤土，高程区为粉砂土；低程区土壤总有机碳、全氮、铵态氮和pH值等与高程区相比无显著差异，而其硝态氮、有效磷、全钾和速效钾含量低于高程区，全磷含量却恰好相反.（2）调查期间，南荻的分布格局随着植物的生长由均匀分布逐渐变为聚集分布，低程区聚集强度更大；（3）南荻的生物量和高度均随时间增长而迅速增加，且低程区的总生物量和增长量均高于高程区；南荻的密度和基径随时间增长而增加，之后趋于平稳，且低程区均高于高程区.结果分析表明，水位高程差异引起的土壤含水量的显著变化可能是影响南荻分布格局和生长动态最重要的因素.因此，适度地调控水位、增加土壤水分含量可能是控制南荻群落扩张的重要措施.In this study, the population distribution patterns and growing status of Triarrhena lutarioriparia along a gentle elevation gradient were analyzed based on an investigation of the fixed quadrat plot and a method of variance to mean ratio in a typical beach of Lake Dongting wetlands. The results indicated that (1) soil moisture content was significantly higher in the low altitude areas than in the high altitude areas. Soil particle composition of low altitude areas was significantly different from that of high altitude ar⁃ eas. Soil pH was all alkaline. There was also no significant difference in soil total organic carbon, total nitrogen, ammonium nitro⁃ gen content and pH, while soil nitrate nitrogen content in low altitude areas was significantly lower than that in the high altitude ar⁃ eas. Soil total phosphorus content was significantly lower in high altitude than that in low altitude, while available phosphorus, total potassium and available potassium showed opposite patterns. (2) The population distribution patterns of T. lutarioriparia in both low and high altitude areas were all changed from a uniform distribution to an aggregated pattern, while the aggregation intensity was greater in the low altitude areas. (3) The biomass of T. lutarioriparia accumulated rapidly along with the time going, which was significantly lower in the low altitude areas than in the high areas. Density and basal diameter of T. lutarioriparia increased sig⁃

Life forms and ecotypes of wetland plants at Lake Dongting wetlands

The relationship between plant community structure and its environment by analyzing plant life forms and plant ecotypes has important significance for the occurrence, development and succession law of plant community. An investigation was made on the species life form and ecotypes of wetland plants in Lake Dongting wetlands. Herbs are the dominant growth form, followed by li⁃ anas, but trees are scarce. Therophytes are major life forms, followed by geophytes and hemicryphytes, and phanerophtes and chamaephytes were the least in Lake Dongting wetlands. The proportion of phanerophtes and chamaephytes in different communities and the same life in different plant communities increased with the elevation. Hygrophytes is major ecotype according to water re⁃ quirement. Neutral soil plant is dominant ecotype based on soil pH requirement. Heliophytes is dominant ecotype according to light intensity demand. The depositions of plants are major ecotype according to responses sediment ubrial. Heliophytes, xerophyte, mes⁃ ophyte, alkaline plant, neotrophilous and burial intolerant plant distribute mainly in low⁃elevation sites. Shade⁃demanding plant, shade⁃enduring plant, acid plant, alkaline plant and burial intolerant plant species also increased with elevation. In Lake Dongting wetlands, the proportion of plants which can adapt to both flooding and sedimenting processes simultaneously is high. Water is the key factor determining the plant distribution of different ecotypes. Species and ecotypes were more diverse in intermediate⁃ and high⁃elevation sites.

Non-additive effects of water availability and litter quality on decomposition of litter mixtures

Non-additive (synergistic or antagonistic) effect, a common phenomenon for the decomposition of mixed litter in nature, is usually regulated by litter quality and environmental factors. In this study, we investigated decomposition rates and nutrient (C, N, and P) dynamics in response to water availability in six litter treatments using plant material from Dongting Lake, China. Three single-litter treatments (leaves of Carex brevicuspis, leaves of Miscanthus sacchariflorus, and stems of M. sacchariflorus) and three mixed-litter treatments (1:1 mixtures of single litters) were incubated at three levels of water availability (20%, 46%, and 100% saturation) for 120 days in a mesocosm experiment. Decomposition rates for single-litter treatments were ranked: M. sacchariflorus leaves > C. brevicuspis leaves > M. sacchariflorus stems. Decomposition rates generally increased with increasing water availability. Antagonistic or additive interactions occurred in the M. sacchariflorus leaves + M. sacchariflorus stems treatment, and synergistic interactions occurred in the other two mixed-litter treatments. N content and lignin loss rate of M. sacchariflorus leaves and M. sacchariflorus stems were increased by mixing with C. brevicuspis leaves. The magnitude of synergistic interactions increased with increasing water availability and the opposite was true for antagonistic interactions. These data suggest that the direction of non-additive effects is dependent on litter quality, while the magnitude is regulated by water availability.