Coalescence of soil microbial communities: consequences, mechanisms, and influential factors

Background: Community coalescence is a major manner of microbial dispersal and a fundamental process of microbial community assembly, yet little is known about its ecological effects, mechanisms, and influential factors. Here, a series of microcosmic experiments including soil mixing, sterilization, as well as microbial extraction and inoculation, were performed to address the knowledge gaps. Results: We found that most physicochemical and microbial properties of the coalesced soils exhibited intermediate characteristics compared to the original soils. Weighted species additive effect emerged as the primary driver for soil microbial community coalescence, with contributions reaching 58.44% (prokaryotes) and 51.57% (fungi). In contrast, the contributions from environmental selection were only less than 20%. Upon the removal of soil particle barrier effects, the contributions of abiotic and biotic environmental selection to soil microbial community coalescence increased to 34.60% and 23.76%, respectively. However, their interactions substantially offset the main effects of abiotic and biotic environmental selection. Original soil differences, mixing ratios, and priority effects were critical factors affecting the consequences of soil microbial community coalescence. Nevertheless, the mechanisms underlying microbial community coalescence were similar under different mixing ratios. Conclusions: Our findings underscore the predictability of soil microbial community coalescence, providing critical insights into comprehending microbial community assembly mechanisms.