The effects of non-rainfall moisture on fungal communities and standing grass litter decomposition in a hyperarid desert

Although drylands represent over 40% of the Earth's land surface, we still lack a strong understanding of what controls carbon cycling in these systems. Decomposition of aboveground standing litter is an important, though often ignored, component of C cycling in drylands and recent work has begun to highlight the central role that non-rainfall moisture (NRM; fog, dew, and high humidity) can play in this process. However, we still know relatively little about how decomposers themselves respond to different moisture regimes and how this may affect overall decomposition rates. We examined the fungal communities on standing grass litter at two sites in the hyperarid Namib Desert (an NRM-dominated zone and a rain-dominated zone) to see how local moisture regimes influence decomposers. While fungal communities differ between the sites, we found a core fungal taxa that dominates litter at both locations. Mass loss rates on sterile litter were 380% higher in the NRM zone than in the rain zone, highlighting the importance of NRM for fungal decomposition, especially in a rain-sparse system. Finally, reciprocally transplanting litter revealed that while all litter decomposed faster in the NRM-zone, communities from the NRM-dominated zone seemed more sensitive to changing moisture regimes than did those originating in the rain zone. Understanding how moisture regimes shape litter-associated microbial communities in drylands can help us make more informed predictions of how C-cycling processes in these systems may change under future climate conditions.