Spatial Heterogeneity of Resource Availability Drives Soil Bacterial Community Assembly Along the Sandy Coast of Southern China

Abstract

The scarcity of resources is prevalent in natural microbial communities, affecting biodiversity and coexistence, yet its intricate impacts on community assembly remain incompletely understood. Here, based on the relative importance of geographic, climatic, environmental, and biotic factors on bacterial community composition, we examined the bacterial community assembly processes in low-resource soil patches along the sandy coast of Southern China. Our study revealed a slightly decreasing trend in bacterial community similarity with increasing geographic distance, while the spatial heterogeneity of soil resource availabilities, including total nitrogen (TN), ammonium (NH4+-N), and total phosphorus (TP), explained 81% of the total variation in the soil bacterial community. Notably, the similarity of soil bacterial community increased with resource availabilities. By incorporating the species co-existence characteristics of bacterial communities, we demonstrated a correlation between increasing bacterial community similarity and an escalation in negative biological interactions, primarily competition, attributed to increased nitrogen (N) availability. Specifically, N was identified as the primary limiting resource for bacterial communities and played a key role in shaping bacterial communities. Furthermore, a significant transition in bacterial community assembly was observed, shifting from stochastic processes in low-resource conditions to more deterministic processes as resource availability increased. The deterministic selection was inherently linked to the dynamics of co-existence within the bacterial community. Elevated N availability, rather than alleviating limitations and promoting biodiversity, led to heightened activity of microbial enzymes involved in N acquisition (NAG and LAP) and decreased complexity of co-occurrence networks. Additionally, under low N availability, microorganisms primarily engaged in positive biological interactions, while high N availability fostered mainly negative interactions. These processes deterministically select specific communities dominated by highly competitive species with strong niche overlaps. Our study offers novel insights into the biogeographic patterns of soil bacterial communities through which resource availability shapes their compositions with potential ecological consequences, including future seedling establishment and the ability of belowground communities to resist disturbances.

Keywords: Soil resource availability, Soil bacterial community, Deterministic processes, Species co-existence, Sandy coastal ecosystems