Assembly Processes, Ecological Strategies, and Functional Potentials of Abundant and Rare Microbial Taxa in Biological Soil Crusts from Different Arid Regions

Abstract

Biological soil crusts (BSCs) cover about 40% of the land surface in arid and semi-arid areas and play crucial roles in biogeochemical cycling and ecosystem functioning. Bacteria and fungi constitute the central active populations of BSC microbial communities, with abundant and rare taxa undertaking different roles. We determined the assembly patterns, ecological strategies, and functional potentials of abundant and rare taxa in bacterial and fungal communities during BSC development in the Tengger Desert and the Loess Plateau. The assembly processes of abundant taxa and permanently rare bacteria were dominated by stochasticity, primarily influenced by dispersal limitation in both areas. In contrast, homogeneous selection was dominant in transiently and conditionally rare taxa and deterministic selection pressure was more substantial in the Tengger Desert due to its relatively poorer nutrients. 16S rRNA operon copy numbers significantly decreased from abundant to rare bacterial taxa with succession, indicating a shift from r-strategies to K-strategies during BSC development in both areas. Rare bacteria had higher functional potentials in metal and non-metal metabolism than their abundant counterparts, while abundant fungi exhibited higher potentials than rare fungi. Stronger functional gene interactions between abundant and rare taxa were observed in the Tengger Desert. Soil carbon was a significant limiting factor for rare taxa in the Tengger Desert, whereas total phosphorus and available nitrogen were more limiting on the Loess Plateau. These findings indicated that nutrient-limiting conditions differentially altered assembly processes and functional potentials between rare and abundant species, but ecological strategies shifted with succession at the community level.

Keywords: Abundant taxa, Assembly process, Biological soil crusts, Functional genes, Rare taxa, r/K-strategies