Dynamic microbial assembly processes correspond to soil fertility in sustainable paddy agroecosystems

Abstract

Abstract Micobial community (diversity and functional traits) underpin the sustainability of agroecosystems. Assembly processes influence microbial community composition and in turn determine their functional traits. However we have a poor understanding of how assembly processes that govern microbial community interact through time to maintain soil fertility. Flooded rice fields are one kind of agroecosystems with high level of sustainability. Ancient rice paddies have a history of cultivation spanning hundreds or thousands of years and thus provide an ideal opportunity to explore relationships between community assembly processes and agroecosystem sustainability. In this study, we used statistical null models to evaluate temporal patterns of bacterial community assembly processes along rice cultivation years and their associations with increases in soil fertility in paddy agroecosystems. We found that stochasticity was a persistent force structuring paddy soil microbial communities, putatively due to frequent flooding that facilities dispersal. However, determinism gradually increased over centuries of agriculture and corresponded to increases in soil fertility. Accordingly, multifunctionality, calculated using enzymes catalysing key soil functions in carbon, nitrogen, phosphorous and sulphur cycling significantly increased along rice cultivation years. We therefore propose that balanced assembly processes preserve a diverse array of traits that can dominate under various circumstances while also allowing for particular traits to be selected for by soil fertility, thus supporting multifunctionality that underpins agroecosystem sustainability. In total, our results highlight that knowledge on temporal microbial assembly processes, community composition and ecological function in the context of soil fertility is key to understanding ecological mechanisms maintaining agroecosystem sustainability. A free Plain Language Summary can be found within the Supporting Information of this article.