Jiang Lin
School of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, Georgia 30332, USA.
Ecology. 2007 May;88(5):1075-85. doi: 10.1890/06-1556.
I assembled bacterial communities to explore the effects of bacterial diversity on multiple ecosystem functions, including bacterial community biovolume, decomposition of particulate organic matter, and biomass transfer to the next trophic level. The experiment used a two-way factorial design with four levels of bacterial diversity (one to four species) and the absence/presence of a bacterivorous ciliated protist Tetrahymena pyriformis as two main factors, and all possible combinations of the four bacterial taxa nested within each diversity level. Bacterial community biovolume increased as bacterial diversity increased, a result due largely to positive selection effects. Decomposition and consumer abundance, however, were unaffected by bacterial diversity, though both varied among bacterial composition treatments. Negative selection effects, the dominance of species that do not contribute significantly to ecosystem functioning, accounted for the lack of diversity effects on decomposition and consumer abundance. The presence of Tetrahymena reduced bacterial community biovolume but increased decomposition, without altering the diversity-functioning relationships. Decomposition was strongly linked with consumer abundance such that communities supporting larger consumer biomass exhibited higher decomposition rates. This study suggests that if the negative selection effect is common, as it might be when examining ecosystem variables other than biomass (due to the presence of keystone species that can contribute disproportionably to ecosystem functioning relative to their abundances), basic bacteria-mediated ecosystem processes, such as decomposition and energy transfer to the next trophic level, may not increase with bacterial diversity.
我构建了细菌群落，以探究细菌多样性对多种生态系统功能的影响，这些功能包括细菌群落生物体积、颗粒有机物的分解以及生物量向更高营养级的转移。该实验采用双向析因设计，将细菌多样性的四个水平（一至四种）以及食细菌纤毛虫梨形四膜虫的有无作为两个主要因素，并且在每个多样性水平内嵌套了四种细菌类群的所有可能组合。细菌群落生物体积随着细菌多样性的增加而增大，这一结果在很大程度上归因于正向选择效应。然而，分解作用和消费者丰度不受细菌多样性的影响，尽管它们在不同细菌组成处理之间存在差异。负向选择效应，即对生态系统功能贡献不大的物种占据主导地位，导致了细菌多样性对分解作用和消费者丰度缺乏影响。四膜虫的存在降低了细菌群落生物体积，但增加了分解作用，而没有改变多样性与功能之间的关系。分解作用与消费者丰度密切相关，以至于支持更大消费者生物量的群落表现出更高的分解速率。这项研究表明，如果负向选择效应很常见，就像在研究除生物量之外的生态系统变量时可能出现的情况那样（由于存在相对于其丰度对生态系统功能贡献不成比例的关键物种），那么诸如分解作用以及能量向更高营养级转移等基本的细菌介导的生态系统过程可能不会随着细菌多样性的增加而增强。
