环境筛选和扩散限制在地表和地下螨群落物种共存中的调控作用

识别扩散限制和环境筛选在群落物种共存中的相对作用,是土壤动物群落物种共存机制研究的重要内容,然而少有针对地表和地下土壤动物群落的探讨。在三江平原农田生态系统,设置一个50 m×50 m的空间尺度,探讨环境筛选和扩散限制对地表和地下土壤螨群落物种共存的调控作用。基于Moran特征向量图(MEMs)和变差分解的方法来区分环境筛选和扩散限制的调控作用;采用偏Mantel检验进一步分析环境距离和空间距离的相对贡献;使用RDA分析环境因子对螨群落物种组成的解释能力。变差分解结果表明,空间变量对地表、地下和地表-地下土壤螨群落具有较大的显著方差解释量,而环境变量和空间环境结构的解释量相对较小且不显著;偏Mantel检验没有发现环境距离或空间距离的显著贡献;RDA分析表明土壤p H值、大豆株高和土壤含水量对土壤螨群落具有显著的解释能力,说明环境变量对螨群落物种组成的重要作用。研究表明,在三江平原农田生态系统,地表和地下土壤螨群落物种共存主要受到扩散限制的调控作用,同时环境筛选的调控作用也不容忽视。

Relative contributions of environmental filtering and dispersal limitation in species co-occurrence of above- and below-ground soil mite communities

One of the most important topics in community ecology is identifying the relative contributions of dispersal limitation and environmental filtering in community construction. However, the relative roles of these processes in above- and below-ground soil organism communities are still not well known. In order to reveal the relative contributions of environmental filtering and dispersal limitation in above- and below-ground soil mite community compositions, a small-scale plot (with a spatial extent of 50 m×50 m and a spatial resolution of 5 m×5 m) was established in a farmland of the integrated experimental field of a wetland, the Sanjiang Mire Wetland Experimental Station, Chinese Academy of Sciences. The plot was equally divided into 100 subplots, and samples for investigating soil mite communities and environmental factors were collected from the bottom left-hand corner of each subplot in August and October in 2011, respectively. Soil corner samplings and pitfall traps were used to capture soil animals in above- and below-ground communities, respectively. Moran''s eigenvector maps (MEMs) were calculated to model spatial components in both months. Variation partitioning (based on partial redundancy analysis, pRDA) was used to estimate and test the proportion of total variation explained purely by environmental factors and spatial variables in soil mite community compositions. Furthermore, the partial Mantel test was selected to analyze the relationships between community dissimilarity and environmental and spatial distances. Finally, redundancy analysis (RDA) was performed to unveil the relative importance of the environmental variables on soil mite community composition. In total, 12 soil mite species were captured in the experiment. In August, 1, 6, and 6 significantly positive MEMs were selected for above-ground, below-ground, and aboveground-belowground (a combination of above- and below-ground) soil mite communities, respectively; 3, 8, and 7 significantly positive MEMs were selected for these communities in October. The results of variance partitioning showed that 3.8%, 12.8%, and 11.1% of the total variation was explained by spatial and environmental variables in the above-ground, below-ground, and aboveground-belowground soil mite communities in August, respectively; these values were 6.6%, 18.4%, and 16.9% in October. The relatively large and significant variation was attributed to purely spatial variables in all three types of soil mite communities in both months, whereas the contributions of purely environmental variables and spatially structured environmental variation were relatively low and non-significant. The partial Mantel test showed no obvious contribution of spatial or environmental distances for all soil mite communities. Based on the results of RDA analysis, soil pH and the average height of soybean explained a significant portion of the variance in August for all communities. In October, soil water content and soil pH explained a significant portion of the variance for the above-ground and aboveground-belowground soil mite communities. These results suggested that dispersal limitation is an important regulator in the composition of above- and below-ground soil mite communities in the farmland of the Sanjiang Plain at a small scale (50 m). However, the relative contribution of environmental filtering should not be overlooked. Collectively, construction of the above- and below-ground soil mite communities appears to be governed by niche- and neutral-based theories simultaneously at the small scale.