延河流域植物群落功能性状对环境梯度的响应

研究群落水平上的植物功能性状特征及其随环境梯度的变化规律,对认识不同环境梯度下植物群落的形成及其对环境的适应机制具有重要意义。以延河流域不同环境梯度下的稳定的自然植物群落为对象,测量了植物群落组成物种的叶厚度、比叶面积、叶组织密度、比根长、根组织密度、单位质量叶氮含量、单位质量根氮含量、种子质量、种子体积等9个性状,然后以物种重要值为基础加权平均得到各个性状在群落水平上的平均值(即群落性状值);以现有的环境因子栅格图为基础,利用ArcGIS提出各群落对应的环境因子值,同时测定各个群落的土壤水分,分析群落各性状值与环境因子的关系,并建立关系模型。结果表明:在群落水平上,9个植物功能性状分别与13个环境因子存在不同程度的相关性,同时这9个植物功能性状对8个环境因子梯度(土壤水分、年4-10月平均气温、年7-9月总降雨量、降雨季节变化、年平均降雨量、年平均蒸发量、坡度、坡向)的响应特征较好,不同植物功能性状间具有较好相关性。群落水平上植物功能性状及其组合随环境梯度的规律性变化,反映了延河流域植被群落构建过程中环境对功能性状的筛选效应。该研究结果对该区的植被恢复重建的物种选择及植被布局规划具有重要的实践意义。

The response of community-weighted mean plant functional traits to environmental gradients in Yanhe river catchment

Plant functional traits reflect the responses of plants to environmental changes and are key elements in studies of the relationship among plant individuals, ecosystem functions and environment factors. The relationship between plant functional traits and environment has become an important topic in phytoecological research. The characteristics of plant functional traits at the community level and their variations induced by environmental changes are important to understand the development of plant communities under different situations and their adaptation strategies. In order to understand how plant functional traits change along the environmental gradients at the community level, and to find out which environmental factors control this process in Yanhe River catchment, we measured nine plant functional traits in typical plant communities along different environmental gradients. Soil water in the field was measured as one environmental factor, and the rest environmental factors relating to climate and topography were calculated and interpolated under the ArcGIS platform. The nine plant functional traits assessed included leaf thickness, specific leaf area, specific root length, leaf density, root density, leaf nitrogen per mass, root nitrogen per mass, seed mass, seed volume. Weighted mean values of the nine traits were then calculated referring to the importance values of different species within communities. Then community-weighted mean trait values were regressed against environmental variables. The results revealed a linear response for the community-weighted mean trait values compared to eight environmental variables. Soil water up to a depth of 200 cm, average annual evaporation and aspect significantly affected the leaf thickness at the community level(P<0.05). The specific leaf area at the community level was influenced mainly by total annual precipitation from July to September. Meanwhile, the total annual precipitation from July to September, aspect and soil water up to a depth of 200 cm significantly influenced the mean leaf density at the community level(P<0.05). Aspect resulted in the greatest variation in specific root length and root nitrogen per mass. Average annual precipitation was the most important factor in determining root density. The average annual temperature from April to October had a significant impact on leaf nitrogen per mass at the community level. Average annual precipitation, total annual precipitation from July to September, seasonal annual precipitation and slope exhibited the greatest influences on the seed mass, however, the seed volume was influenced primarily by the average annual precipitation and slope. Moreover, the nine plant functional traits evaluated at the community level were closely related and strongly correlated to the environment. This results showed that an environment filter was likely involved in the process of community assembly within the study area. For example, in the wet area of Yanhe river catchment, plant communities tended to have low specific leaf area and high leaf density, as well as large and heavy seeds, while plant communities in the dry region exhibited thick leaves, small, light seeds, and produced less aboveground biomass and more underground biomass. These conclusions can serve as an important guide for vegetation rehabilitation in hilly area of Loess Plateau.