Sarquis, A. | bioRxiv Science

bioRxiv2026

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.

ecology↗

bioRxiv2025

Plant litter decomposition in global drylands is better predicted by precipitation seasonality and temperature than by aridity

Understanding the global carbon (C) balance in terrestrial ecosystems is crucial for predicting their current and future roles as C sources or sinks in the context of global change. Drylands, covering nearly 45% of Earths land surface, contribute significantly to net primary production (NPP) and influence the interannual variability of the terrestrial C sink. However, the controls on plant litter decomposition, a major pathway of C release, remain unclear in these ecosystems. Here, we present a global analysis of plant litter decomposition in drylands, using a dataset from 116 sites across five continents spanning diverse climates and ecosystems. We found that litter decomposition does not correlate with mean annual precipitation (MAP) at the global scale, challenging the paradigm that water availability is the primary constraint on ecological processes in drylands. Instead, our analysis identifies mean annual temperature (MAT), precipitation-temperature synchrony, precipitation variability, and cloud cover frequency as key drivers. Specifically, our model predicted faster decomposition rates for warmer and more monsoonal ecosystems, but vary independently of MAP. Additionally, decomposition correlated positively with both lignin and nitrogen content, in contrast to the negative lignin-decomposition relationship commonly observed in mesic ecosystems. These findings suggest a fundamental mismatch between aridity and its expected effects on decomposition rates in terrestrial ecosystems. Given the ongoing expansion of drylands, rising temperatures and changes in precipitation variability under climate change; our results underscore the need to refine decomposition models beyond traditional aridity frameworks. Such refinement is essential for accurately predicting dryland contributions to the global C balance.

ecology↗