Microbial diversity loss and wheat genotype-triggered rhizosphere bacterial and protistan diversity constrain soil multifunctionality: Evidence from greenhouse experiment

Agricultural soil multifunctionality is greatly impacted by belowground processesdriven by a complex group of microorganisms that change during plant growth. While most studies in microbial diversity and multifunctionality have focused on soil bacteria or fungi, they have largely overlooked the influence of key microbiome predators- the protists and other microorganisms. We manipulated microbial alpha diversity using a dilution-to-extinction approach. Wheat varieties were employed to investigate the effects of manipulated microbial alpha diversity on rhizosphere microbes (including bacteria and eukaryotes-fungi and protists) and soil multifunctionality (nutrient cycling, organic matter decomposition, and plant productivity) during a two-month re-colonization period. The recovery and re-colonization of the belowground microbial communities were primarily influenced by dilution rather than wheat variety. Random forest (RF) analysis indicated that changes induced by dilution and plant variety in bacterial and protistan assembly in the rhizosphere had stronger effects on soil multifunctionality than those in bulk soil and root endosphere. Reduced microbial diversity led to a decrease in specific functions, such as phosphorus mineralization and nitrification, but did not affect broad functions like microbial respiration and organic decomposition. The rare taxa, such as those belonging to bacterial Burkholderiaceae, Rhizobiaceae, and Sphingobacteriaceae, and protistan Cercozoa, Ochrophyta, and Chlorophyta crucially influenced soil multifunctionality. The critical role of rhizosphere protistan and bacterial communities in soil multifunctionality underscores the importance of plant-induced shifts in belowground microbial assembly for the resilience of soil multifunctionality to biodiversity loss Moreover, rhizosphere rare bacterial and protistan taxa contributed more to ecosystem functions than expected based on their abundance.