The role of photodegradation in plant litter decomposition in grassland ecosystems

Abstract

Decomposition of plant litter is the primary process by which carbon and nutrients are returned from plants to the soil and atmosphere. Although plant litter decomposition is primarily driven by plant litter chemistry, temperature, and precipitation these factors have failed to fully explain decomposition patterns in arid and semiarid grassland ecosystems. In my dissertation, I tested the hypothesis that solar radiation, particularly in the UV range (280-400 nm) contributes to the decomposition process in these systems via the process of photodegradation. In a three-year field study in the semiarid shortgrass steppe in Colorado, I examined whether photodegradation by UV radiation played a role in plant litter decomposition and whether the role of photodegradation in the decomposition process was affected by plant litter chemistry and precipitation. In a series of laboratory experiments, I examined the pathways by which mass is lost via photodegradation. In a two-year cross-site field experiment, I examined whether photodegradation may explain the difference in litter decomposition patterns among mesic, semiarid, and arid grassland ecosystems. The combined results of this research show that photodegradation is an important process in plant litter decomposition in mesic grassland ecosystems as well as arid and semiarid grassland ecosystems, accounting for up to 50% of litter mass loss. Results also show that litter mass loss via photodegradation is the result of photochemical production of carbon dioxide, which can be up to 4 g C m-2 y-1 in arid ecosystems. This research has important implications for future basic research in biogeochemical modeling, photochemistry of natural compounds, and plant litter decomposition in arid ecosystems.