Research Professor School of Earth and Space Exploration, Arizona State University Tempe, Arizona, United States
Litter decomposition is a key ecosystem processes regulating biogeochemical cycling, and yet accurately predicting litter decomposition in dryland ecosystems has long challenged ecologists. Data suggest that the mismatch between measured and modeled dryland decomposition rates may be, at least in part, a function of several ‘dryland mechanisms’ that are currently prevalent in dry regions but typically uncommon in mesic systems. In particular, photochemical degradation, thermal degradation, and soil-litter mixing have all been shown to account for a portion of the model-measurement mismatch under dryland conditions. A new synthesis of dryland decomposition data suggests that the importance of these three dryland mechanisms differs substantially among vegetation patch types, with differences in abiotic conditions among patch types affecting the relative importance of these mechanisms. The three dryland mechanisms appear to have interactive effects on decomposition, challenging our current experimental approaches that typically have limited capacity to consider multiple interacting decomposition drivers. The synthesis data also illustrate a current mis-alignment between dominant drivers and the spatial context of decomposing litter, with the majority of dryland litter collected underneath objects such as plant canopies that moderate the microclimate but the majority of decomposition studies taking place in intercanopy environments. Results of this synthesis effort suggest that the importance of the three ‘dryland mechanisms’ for litter decomposition are all likely to become increasingly important at both short- and long- temporal scales with increasing drying and warming of historically mesic systems. Improved understanding of dryland mechanisms is critical for improving understanding of ecosystem functioning of globally-extensive drylands. However, the emerging nature of these dryland decomposition mechanisms into historically mesic systems suggest that improving understanding of the dryland mechanisms will help to better predict ecosystem functioning in dryland and mesic systems under future climate conditions.
