Biological soil crusts and wetting events: Effects on soil N and C cycles

• We assess how the biocrust and the length of wetting events determine soil variables.
• We analyze soil variables related to C and N cycles on biocrust and bare ground.
• Longer wetting events kept higher mineral N and organic N and C mainly in biocrust.
• Longer wetting events may enhance the decomposition rate mainly in biocrust.
• Changes in wetting events and the biocrust coverture may alter future soil community.

Biological soil crust (BSC) communities control many functional processes in arid and semiarid ecosystems, where biological activity is closely influenced by soil wetting. Our goal was to analyze how the length of wetting events and the presence of BSC determine soil variables related to carbon (C) and nitrogen (N) cycling in a semiarid ecosystem. We applied three watering treatments (one, six and ten days) on soils from two microsites (BSC and bare ground) in a microcosm experiment. We analyzed multiple variables related to N and C cycling (N in microbial biomass [MB–N], dissolved organic nitrogen [DON], NH4+–N, NO3−–N, resin–NH4+–N and resin–NO3−–N, phenols and carbohydrates). For all treatments, minimum DON concentration appeared earlier in BSC than in bare ground, while maximum NO3− peaks appeared earlier in BSC than in the bare ground. Increases of NH4+ were only perceptible under BSC. Our results showed that longer lasting wetting events kept higher mineral and organic N as well as labile organic C in soils under BSC, which suggest that longer wetting events may be related to an enhancement in the decomposition rate that compensate for nutrient losses associated to short lasting wetting events. This trend is much less obvious in bare ground than under BSC. Our data suggest that changes in the length of wetting events and the presence of BSC with climate changes could alter future soil community structure and function.