Carbon utilization, microbial biomass, and respiration in biological soil crusts in the Negev Desert

Biological soil crusts (BSCs) and the soils directly below crusts (SDBCs) (0–5 mm) were collected in the Negev Desert (Israel) during the wet and dry seasons of 2007 and 2008, gently separated, and microbial basal respiration, microbial biomass carbon (Cmic), carbon (C) source utilization rates, and catabolic diversity were analyzed using MicroResp™ plates. The seasonal-change patterns of these parameters were similar to those of soil organic C (C_org) in the BSCs, i.e., increases were observed during the dry seasons relative to the wet seasons. Few seasonal variations in qCO₂ and C_mic/C_org in the BSCs indicated that the increases in crustal organism basal respiration and C source utilization rates can be attributed to microbial propagation as a result of the increases in available C during the dry seasons. High frequency of rain events, with precipitation higher than 0.1 mm during spring, can enable crustal organisms to maintain photosynthetic activity and can facilitate microbial propagation and C_org accumulation in the BSCs. The seasonal dynamics of the four biotic parameters in the SDBCs were the opposite of those of the BSCs, and C source utilization rates and catabolic diversity were higher than in the BSCs during the wet seasons. Downward migration of exopolysaccharides, crustal organism cell contents, and intracellular solutes with water infiltration can increase C and nutrient availability and enhance microbial catabolic activities and propagation in the SDBCs.