This collaborative project seeks to understand the fundamental drivers of decomposition in arid grasslands (http://www.snr.arizona.edu/project/decomposition). Recent independent studies have suggested that both UV and soil erosion/deposition play critical roles in this important ecosystem process, potentially in contrasting ways. This project tests the hypothesis that radiant energy (UV) and soil movement drivers interact, such that UV effects on litter decomposition predominate up to a certain level of soil deposition and are then negated. Therefore, shifts in grass-woody plant abundance in drylands affect decomposition rates by mediating soil transport processes that determine the extent of litter-soil contact; and that enhancement of microbial activity by soil accumulation more than offsets associated reductions in UV photodegradation. This is a collaborative proposal between the University of Arizona (Steve Archer, Dave Breshears), New Mexico State University (Heather Throop), University of Kentucky (us), and Loyola University New Orleans (Paul Barnes). We provide part of the microbial component of this project. We have developed phospholipid fatty acid profiles of the litter as it degrades, which tells us something about the dominant microbial taxonomic groups present in the litter and their response to environmental drivers like UV, soil mixing, and water availability. We are currently expanding this work onto the European continent, looking at the role of UV in litter decomposition in cork oak woodlands in Portugal that are being invaded by a native shrub - Cistus ladanifer.