Addressing the dryland decomposition conundrum by integrating vegetation structure, soil transport, and ultraviolet (UV) photodegradation

Background/Question/Methods Decomposition of organic matter is a crucial component of biogeochemical cycles that influences nutrient availability, productivity, and community composition. Decay rates in mesic systems are generally quite successfully predicted by models driven by climatic variables. In contrast, factors controlling decomposition of litter in arid and semi-arid systems remain poorly understood, with an unresolved disconnect between measured and modeled decay rates. Recent research on decomposition in drylands suggests several key drivers of dryland decomposition have been historically overlooked. In particular, UV photodegradation and soil transport processes, both a function of vegetation structure, may strongly influence dryland decomposition dynamics.

Results/Conclusions In the Sonoran Desert, we have found strong positive correlations between soil transport into litter bags and decomposition rates. In the Chihuahuan Desert, manipulations of grass cover strongly influence soil transport rates and subsequent rates of leaf litter decomposition. In laboratory incubations, soil deposition appears to counteract UV photodegradation. We use these data to suggest an expanded framework for studying dryland litter decomposition that explicitly addresses vegetation structure and its influence on decomposition. Spatial heterogeneity of vegetation in dryland systems necessitates considering how the spatial and temporal context of vegetation influences interactions between soil transport patterns and UV photodegradation, both of which may in turn affect abiotic and biotic decomposition processes.