Spatial scale modulates stochastic and deterministic influence on biogeography of photosynthetic biofilms in Southeast Asian hot springs.

Hot springs, with their well-characterized major abiotic variables and island-like habitats, are ideal systems for studying microbial biogeography. Photosynthetic biofilms are a major biological feature of hot springs but despite this large-scale studies are scarce, leaving critical questions about the drivers of spatial turnover unanswered. Here, we analysed 395 photosynthetic biofilms from neutral-alkaline hot springs (39-66 °C, pH 6.4-9.0) across a 2100 km latitudinal gradient in Southeast Asia. The Cyanobacteria-dominated communities were categorized into six biogeographic regions, each characterized by a distinct core microbiome and biotic interactions. We observed a significant decline in the explanatory power of major abiotic variables with increasing spatial scale, from 62.6% locally, 55% regionally, to 26.8% for the inter-regional meta-community. Statistical null models revealed that deterministic environmental filtering predominated at local and regional scales, whereas stochastic ecological drift was more influential at the inter-regional scale. These findings enhance our understanding of the differential contribution of ecological drivers and highlight the importance of spatial scale in shaping biogeographic distributions for microorganisms.