Divergence among biological soil crust communities developing under different environmental conditions

Abstract

Question: The distribution of biological soil crusts (BSCs) is critical for the functioning of dryland ecosystems. Recent studies have proposed alternative successional pathways to explain the spatial variability in BSCs. However, the influence of environmental filtering structuring BSC communities remains unclear. We asked how early BSC assembly varies in response to different abiotic selective factors and whether communities converge or diverge toward the structure of natural communities that develop in different microsites. Location: Semiarid shrubland in Argentina. Methods: We used experimental community assembly, starting with a diverse inoculum containing species pools from different microhabitats (vegetated and interspaces), and examined how single-factor manipulations (water, light and nitrogen) affect community structure under otherwise natural conditions. We repeated the experiment in consecutive years, and evaluated the similarities between the assembled communities and the natural ones from which the inoculum was derived. Results: Frequent watering was essential for promoting BSC growth, and shading and N fertilization led to divergent community structures formed by BSC groups with different functional strategies. Cyanobacteria and cyanolichens dominated the N fertilizer treatment, while mosses and green algae thrived under shade conditions. These communities were similar to natural communities in interspaces and subcanopy microsites respectively. Differences between treatments in species richness and abundance were consistent across years. Conclusions: The research presented here represents the first attempt to assemble multispecies BSC communities for testing ecological hypotheses. The results suggest the relevance of environmental filtering determining alternative BSC community configurations, probably related to physiology-based selection of the BSC components. The existence of divergent assembly patterns does not support the deterministic facilitative model of BSC development that has been widely applied across environments, advancing our previous understanding about BSC dynamics.