Divergence of Biocrust Active Bacterial Communities in the Negev Desert During a Hydration-Desiccation Cycle.

Rain events in arid environments are highly unpredictable and intersperse extended periods of drought. Therefore, tracking changes in desert soil bacterial communities during rain events, in the field, was seldom attempted. Here, we assessed rain-mediated dynamics of active bacterial communities in the Negev Desert biological soil crust (biocrust). Biocrust samples were collected during, and after a medium rainfall and dry soil was used as a control; we evaluated the changes in active bacterial composition, potential function, potential photosynthetic activity, and extracellular polysaccharide (EPS) production. We hypothesized that rain would activate the biocrust phototrophs (mainly Cyanobacteria), while desiccation would inhibit their activity. In contrast, the biocrust Actinobacteria would decline during rewetting and revive with desiccation. Our results showed that hydration increased chlorophyll content and EPS production. As expected, biocrust rewetting activated Cyanobacteria, which replaced the former dominant Actinobacteria, boosting potential autotrophic functions. However, desiccation of the biocrust did not immediately change the bacterial composition or potential function and was followed by a delayed decrease in chlorophyll and EPS levels. This dramatic shift in the community upon rewetting led to modifications in ecosystem services. We propose that following a rain event, the response of the active bacterial community lagged behind the biocrust water content due to the production of EPS which delayed desiccation and temporarily sustained the biocrust community activity.