Aspects of soil lichen biodiversity and aggregation interact to influence subsurface microbial function

Many previous studies have evaluated aboveground-heterotrophic belowground interactions such as plant-soil feedbacks, plant-mycorrhizal fungi associations or plant-actinorhizal symbioses. However, few studies have used biocrusts, which are specialized soil communities of autotrophic cyanobacteria, mosses, lichens and non-photosynthetic fungi and bacteria that are prevalent in drylands worldwide. These communities largely influence ecosystem functioning, and can be used as a model system for studying above-belowground interactions. In this study, we evaluated how biocrusts affect the functional diversity and biomass of microbial diversities beneath biocrusts. We performed two microcosm experiments using biocrust-forming lichens where we manipulated their biotic attributes to test independently the effects of species richness (from two to eight species), composition, evenness (maximal and low evenness) and spatial pattern (clumped and random distribution) on the microbial catabolic profile and microbial functional diversity. Microcosms with a random pattern had a higher microbial catabolic profile than those with a clumped pattern. Significant richness x evenness x pattern and richness x evenness interactions were found when analyzing microbial catabolic profile and biomass, respectively. Microcosms with a random pattern, intermediate number of species, and maximal evenness level had higher microbial catabolic profile. At the maximal evenness level, assemblages had higher microbial catabolic profile and microbial biomass when they contained four species. The richness x evenness x pattern interaction was the most informative predictor of variations in microbial catabolic profile. Our results indicate that soil microorganisms are influenced by biocrusts, just as they are influenced by plants, and highlight the importance of higher order interactions among species richness, evenness, and spatial pattern as drivers of microbial communities. The results also emphasize the importance of studying several biotic attributes simultaneously when studying biocrust-soil microorganism interactions, as in nature, community properties do not exert their influence in isolation.