LAUSR

Abstract Background & Aims We assessed the joint role of shrub cover and UV-B on decomposition in a Sonoran Desert grassland. UV is considered an important driver of biogeochemistry in arid grasslands and shrub proliferation in these landscapes can alter both abiotic and biotic drivers of biogeochemistry. Methods We manipulated ambient solar UV-B exposure of Prosopis velutina leaf litter under and away from shrub canopies and assessed decomposition responses over 320 days. Results Leaf litter mass declined 40% during the first 50 days, but only an additional 10% during the remaining 270 days. Decomposition was slower under shrubs, where ground temperatures and total solar radiation were lower than locations away from shrubs. However, the presence/absence of UV-B radiation had no detectable influence on mass loss either under or away from shrubs. UV-B exposure decreased N immobilization suggesting UV-B photodegradation is facilitating microbial access to litter N. Conclusions Higher decomposition of litter away from shrubs may reflect a combination of greater rates of thermal degradation and photodegradation. While UV-B did not directly influence decomposition rates, exposure may alter litter nutrient dynamics. Our study suggests landscape-scale decomposition could decline with increases in woody plant canopy cover owing to shrub-driven changes in microclimate.