Biocrust adaptations to microhabitat alter bacterial communities in a semiarid ecosystem

Aims: Biocrusts, the living skin of dryland ecosystems, contain diverse soil microorganisms that are essential to biocrust formation and the maintenance of multiple ecological functions including nitrogen fixation, carbon sequestration, soil stability, and rainfall redistribution. We know that biocrusts are important modulators of the soil microbiomes, however, much less is known about how local conditions influence biocrust adaptation and subsequently alter the soil microbiomes. Methods: To understand the effects of microhabitat on bacterial communities via changes in biocrust traits, we collected biocrusts and analyzed soil microbiomes from eight representative microhabitats present in a semiarid ecosystem from the Chinese Northern Loess Plateau. These microhabitats were located a) outside plant canopy on level land, on shady gentle slope, and sunny gentle slope; b) under plant canopy on level land, on shady gentle, and sunny gentle slope; and c) outside plant canopy on shady and sunny steep slope, respectively. We then used structural equation modeling to investigate the relative contribution of microhabitat factors on important bacterial community metrics through quantifying the changes in biocrust traits. Results: Observed microhabitat conditions significantly (P ≤ 0.033) altered the traits of biocrusts (e.g., thickness, biomass, and chlorophyll content), which were associated with significant changes in the soil bacterial community. For example, the bacterial richness in biocrusts developing under plant canopy, on shady slopes, and on gentle slopes was 20.1%, 19.9%, and 15.4% higher than that of the biocrusts developing outside plant canopy, on sunny slopes, and on steep slopes, respectively. We further showed that microhabitat conditions significantly impacted the network structure of bacterial communities under biocrusts, and structural equation modeling revealed that microhabitat metrics had strong indirect effects on network connectivity through changing biocrust traits. Conclusions: Our findings suggest that microhabitat factors can strongly influence soil bacterial communities via the changes in locally-adapted biocrust traits and soil properties. This knowledge is critical to understand the impacts of changing environments on biocrusts and associated soil bacterial communities, particularly as climate change progresses.