Photodegradation accelerates standing dead litter decomposition in monsoonal mountain grasslands of South America

Plant litter decomposition is the process through which plant-derived organic matter is recycled in terrestrial ecosystems. One of the drivers of decomposition is photodegradation, light-induced reactions that result in litter mass loss and transformations that accelerate the decomposition process. Photodegradation has been mostly studied in arid ecosystems, but mesic grasslands with monsoonal climate have been almost absent in the literature. In these ecosystems, standing dead biomass might remain exposed to solar radiation during dry winters while the effects of photodegradation accumulate. With the start of the warm and humid seasons, biotic decomposition might increase as a consequence of the changes in litter quality caused by sunlight. We aimed to study the impact of different wavelengths of solar radiation on litter mass loss and litter quality changes in a montane grassland with a monsoonal climate. We incubated litter from two dominant grasses under filters that generated treatments of full solar radiation, reduced UV radiation and reduced UV to short-wave visible radiation. We tracked changes in physical litter traits throughout the experiment under the three light treatment levels. We found an increase in litter mass loss due to sunlight exposure for both species, but each species reacted to a different range of wavelengths. We found evidence of enhancement of biotic decomposition by solar radiation (photofacilitation) in one of the two species, through an increase in {beta}-glucosidase enzymatic activity. Seasonality affected litter decomposition of one species only by increasing mass loss depending on whether it was placed in the field during the dry winter or the humid spring. Finally, we found evidence of changes in physical litter traits caused by solar radiation, mainly in leaf mass per area (LMA) and water adsorption capacity. Our results represent the first proof of photodegradation in a productive grassland in this region, and highlight the fact that photodegradation is not constrained only to arid environments. Additionally, this study emphasizes the importance of litter physical traits in regulating carbon cycling through plant litter decomposition in terrestrial ecosystems. Open Research StatementData are not yet provided as the study is currently under peer review. Upon acceptance, data will be archived in Zenodo. However, full datasets can be made available to the editorial board if required for the evaluation of the manuscript.