Sludge bioreactor microcosm study on complex bacterial communities and ecosystem function using 3-CA disturbance at varying frequencies for 35 days

Disturbance is known to affect ecosystem structure, but predicting its outcomes remains elusive. Similarly, community diversity is believed to relate to ecosystem functions, yet the underlying mechanisms are poorly understood. Here, we tested the effect of disturbance on the structure, assembly, and ecosystem function of complex microbial communities within an engineered system. We carried out a microcosm experiment where activated sludge bioreactors operated in daily cycles were subjected to eight different frequency levels of augmentation with a toxic pollutant, from never (undisturbed) to everyday (press-disturbed), for 35 days. Microbial communities were assessed by combining distance-based methods, general linear multivariate models, a-diversity indices, and null model analyses on metagenomics and 16S rRNA gene amplicon data. A stronger temporal decrease in a-diversity at the extreme, undisturbed and press-disturbed, ends of the disturbance range led to a hump-backed pattern, with the highest diversity found at intermediate levels of disturbance. Undisturbed and press-disturbed levels displayed the highest community and functional similarity across replicates, suggesting deterministic processes were dominating. The opposite was observed amongst intermediately disturbed levels, indicating stronger stochastic assembly mechanisms. Trade-offs were observed in ecosystem function between organic carbon removal and both nitrification and biomass productivity, as well as between diversity and these functions. Hence, not every ecosystem function was favoured by higher community diversity. Our results show that the assessment of changes in diversity, along with the underlying stochastic-deterministic assembly processes, is essential to understanding the impact of disturbance in complex microbial communities.

干扰已知会对生态系统结构造成影响，但其引发的结果却难以精准预测。类似地，群落多样性被认为与生态系统功能密切相关，但其背后的潜在机制仍未被充分阐明。本研究以工程系统中的复杂微生物群落为研究对象，探究了干扰对其结构、组装过程及生态系统功能的影响。我们开展了一项微型生态系统（microcosm）实验：将每日循环运行的活性污泥生物反应器，暴露于8种不同频率的有毒污染物投加扰动中，扰动频率覆盖从未投加（未受干扰组）至每日投加（持续扰动（press-disturbed）组），实验周期共计35天。研究通过结合基于距离的分析方法、广义线性多元模型、α多样性（a-diversity）指数，以及针对宏基因组学（metagenomics）与16S核糖体RNA基因扩增子（16S rRNA gene amplicon）数据的零模型（null model）分析，对微生物群落进行了评估。在干扰梯度的两个极端——未受干扰组与持续扰动组——中，α多样性随时间呈现出更为显著的下降趋势，最终形成驼峰型分布模式：中等强度干扰下的群落多样性水平最高。未受干扰组与持续扰动组的群落组成与功能在生物学重复样本间的相似度最高，表明确定性组装过程占据主导地位。中等强度干扰组则呈现出相反的趋势，暗示随机组装机制的作用更强。研究还观测到生态系统功能间存在权衡关系：有机碳去除与硝化作用、生物量生产力之间，以及多样性与上述功能之间均存在权衡现象。换言之，更高的群落多样性并非能够提升所有的生态系统功能。本研究结果表明，若要深入理解干扰对复杂微生物群落的影响，必须同时评估多样性的变化及其背后的随机-确定性组装过程。