Department of Ecology and Evolution, University of Chicago, 1101 E 57th Street, Chicago, Illinois, 60637, USA.
School of Forestry and Environmental Studies, Yale University, 370 Prospect Street, New Haven, Connecticut, 06511, USA.
Ecology. 2018 Apr;99(4):801-811. doi: 10.1002/ecy.2165. Epub 2018 Feb 21.
Environmental conditions exert strong controls on the activity of saprotrophic microbes, yet abiotic factors often fail to adequately predict wood decomposition rates across broad spatial scales. Given that species interactions can have significant positive and negative effects on wood-decay fungal activity, one possibility is that biotic processes serve as the primary controls on community function, with abiotic controls emerging only after species associations are accounted for. Here we explore this hypothesis in a factorial field warming- and nitrogen-addition experiment by examining relationships among wood decomposition rates, fungal activity, and fungal community structure. We show that functional outcomes and community structure are largely unrelated to abiotic conditions, with microsite and plot-level abiotic variables explaining at most 19% of the total variability in decomposition and fungal activity, and 2% of the variability in richness and evenness. In contrast, taxonomic richness, evenness, and species associations (i.e., co-occurrence patterns) exhibited strong relationships with community function, accounting for 52% of the variation in decomposition rates and 73% in fungal activity. A greater proportion of positive vs. negative species associations in a community was linked to strong declines in decomposition rates and richness. Evenness emerged as a key mediator between richness and function, with highly even communities exhibiting a positive richness-function relationship and uneven communities exhibiting a negative or null response. These results suggest that community-assembly processes and species interactions are important controls on the function of wood-decay fungal communities, ultimately overwhelming substantial differences in abiotic conditions.
环境条件对腐生微生物的活性有很强的控制作用，但非生物因素往往不能充分预测广泛空间尺度上的木材分解速率。鉴于物种相互作用对木质素分解真菌活性可能有显著的正、负影响，一种可能性是生物过程是群落功能的主要控制因素，只有在考虑物种关联后，非生物控制才会出现。在这里，我们通过考察木质素分解速率、真菌活性和真菌群落结构之间的关系，在一个因子野外增温和施氮实验中检验了这一假设。我们表明，功能结果和群落结构与非生物条件基本无关，微生境和样地水平的非生物变量最多只能解释分解和真菌活性总变异性的 19%，以及丰富度和均匀度变异性的 2%。相比之下，分类丰富度、均匀度和物种关联（即共现模式）与群落功能有很强的关系，解释了分解速率变化的 52%和真菌活性变化的 73%。群落中更多的正相关物种关联与强烈的分解速率和丰富度下降有关。均匀度是丰富度和功能之间的一个关键中介，高度均匀的群落表现出正的丰富度-功能关系，而不均匀的群落则表现出负或零响应。这些结果表明，群落组装过程和物种相互作用是木质素分解真菌群落功能的重要控制因素，最终压倒了非生物条件的显著差异。
