Background/Question/Methods Most decomposition models assume that litter quality (the relative quantity of soluble C compounds, non-lignified cellulose/hemicellulose, and lignin), air and soil temperatures, and precipitation control decomposition rates. However, in arid regions, UV degradation, the presence and activity of soil micro- and macrofauna, as well as the seasonality of precipitation are very important, but often unappreciated, variables to consider in understanding decomposition rates. However, even among arid ecosystems the relative importance of these factors can vary. In this talk, we will consider the relative importance of a given variable and provide a common conceptual framework by which to compare these differences. We will also present data on decomposition in cool semi-arid deserts and hot deserts to illustrate the controls on decomposition rates in these ecosystems.

Results/Conclusions In all deserts, UV and shredding by wind appear to be the dominant force in aboveground decomposition. In a cool desert ecosystem, plant litter labeled with ¹³C showed almost no movement from the surface to subsurface soils. This was not surprising as this ecosystem lacks substantial numbers of termites, ground-dwelling beetles, or other soil macrofauna that might carry litter beneath the soil surface. However, in hot deserts, beetles and termites can effectively incorporate litter into soils. In cool deserts, the decomposition of belowground materials appears almost exclusively microbial, and concomitant examination of the soil food web shows very low numbers of soil micro- and macrofauna, thus explaining the predominance of microbial processing of belowground materials. We propose that controls on decomposition in arid ecosystems are very different among types of deserts and those in more mesic systems and will require more careful examination before they can be accurately understood and modeled.