Successional biocrust stages on dead shrub soil mounds after severe drought: Effect of micro-geomorphology on microbial community structure and ecosystem recovery

A drought- induced massive shrub death event was observed in a semi-arid region of the Negev Desert, leaving bare soil mounds in place. Hypothesizing that the absence of shrubs would allow biocrust expansion to cover the bare soil mounds, we followed the development of biocrusts on the south and north-facing slopes of the soil mounds over three years. Only after six years, when the mounds were totally flattened, were the water infiltration capacity and soil compaction properties of the developing biocrusts similar to those of the surrounding mature biocrusts. The prokaryotic community structure was exposed by pyrosequencing of 16S rRNA gene amplicons. A principal component analysis indicated that the development of microbial community on the soil mounds was affected at multiple scales, including biocrust successional stage, seasonal effect and the micro-geomorphology of the mound (north vs. south slopes). While the phototroph community structure was most associated with the biocrust successional stage, the heterotroph community structure was mostly season-associated. Compared to the north slope, the south slope exhibited delayed development in all determined parameters; with the addition of lately observed establishment of new shrubs in this site, the results emphasize the importance of the micro-geomorphology in the recovery of the affected ecosystem.