Soil-litter mixing reduces importance of solar radiation and increases microbial decomposition of litter in drylands

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Steven McBride II, Plant and Soil, University of Kentucky, Lexington, KY, Steve R. Archer, School of Natural Resources, University of Arizona, Tucson, AZ, Eva M. Levi, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, Heather L. Throop, Faculty of Natural Resources and Spatial Sciences, Namibia University of Science and Technology, Windhoek, Namibia, Jim A. Nelson and Rebecca L. McCulley, Plant & Soil Sciences, University of Kentucky, Lexington, KY, Paul W. Barnes, Biological Sciences and Environment Program, Loyola University New Orleans

Background/Question/Methods
Litter decomposition is a key ecosystem function that determines rates of carbon and nutrient cycling; however drivers of litter decomposition are poorly understood in dryland ecosystems. Photodegradation by ultraviolet radiation has emerged as a dominant control of decomposition in arid and semi-arid systems, yet microbial decomposition occurs and may be enhanced when litter material is covered with soil - a phenomenon that is promoted by wind and water erosion, both of which are common in drylands. To determine the relative roles of photodegradation and microbial decomposition in full sun and soil-covered environments, we performed a full factorial litter-bag experiment utilizing litter from a native shrub (velvet mesquite) and an invasive grass (Lehmann lovegrass). Over time, litter mass, C, N, phenolics, and microbial community composition were measured.

Results/Conclusions
In full sun, bacterial colonization was inhibited, while it was facilitated when litter was covered with soil. Velvet mesquite decomposed more rapidly than Lehmann lovegrass regardless of soil-coverage treatment, likely due to its lower C:N. Eliminating UV-B had minimal effect on decomposition. Bacteria and fungi both emerged as important regulators of decomposition, and decomposition was indirectly affected by solar radiation, litter C:N, and soil coverage effects on the microbial community. Overall, this study enhances our understanding of litter decomposition in dryland ecosystems by uncovering the factors that drive biotic and abiotic control of this process, and will likely inform models that aim to predict decomposition in dryland ecosystems.