The effect of hydration after long desiccation periods on arid bacterial communities has been debated for many years and different scenarios were suggested. We predicted that like macroorganisms hydration of desert soil will supply microorganisms with much needed water and increase diversity and abundance. We further hypothesized that desiccation will impose water shortage and stress on the bacteria resulting in diversity and abundance reduction.
To test our hypotheses we followed hydration and subsequent desiccation in controlled and field settings. We simulated rain on arid soil columns and linked changes in the active bacterial community to the soil water content. Concomitantly, we followed a major rain event in the Negev Desert while sampling at intervals until the soil was fully desiccated.
Our results suggest that under hydrated conditions active species richness and phylogenetic diversity plummet, while the total abundance of the active bacteria was unscathed. Desiccation of the soil restores the active bacterial diversity and richness while not affecting their abundance. Both the controlled and field environments showed a shift in the dominant bacterial groups during hydration and subsequent desiccation. We suggest that during hydration events, dryland bacteria are involved in complex community dynamics. As moisture in the soil increase gaps between the soil particles are bridged by water, enabling interactions and competition between formally separated communities leading to a decrease in the overall bacterial diversity. When the soil desiccates the pores are again segregated and unique communities are established in each microhabitat thus stimulating bacterial dispersal and diversity.
