Decomposition of dominant grass species is differently affected by sunlight in a mountain grassland

SARQUIS, AGUSTÍN; SIEBENHART, IGNACIO ANDRÉS; MÉNDEZ, MARCELA SOLEDAD; AUSTIN, AMY THERESA

Buenos Aires

Simposio; Frontiers in Bioscience 4 Symposium; 2023

IBIOBA - MPSP

Decomposition of senescent plant tissue (litter) is the first step in the terrestrial carbon (C) cycle and a critical component determining the C balance at the ecosystem scale. Generally, degradation of plant litter is thought to be biotically mediated. But, more recently photodegradation was identified as a control of litter decomposition, that is the set of photochemical reactions generated by the exposure to solar radiation. Sunlight exposure generates oxidation reactions in organic C, which can be released directly to the atmosphere. In turn, photodegradation transforms chemical components of the litter, particularly lignin, making it more decomposable by soil biota, in a process called photofacilitation. We sought to broaden our understanding of the importance of photodegradation by evaluating its importance in a mountain grassland with a monsoonal climate in the Córdoba province of Argentina. We used litter from two dominant bunch grasses: Poa stuckertii and Deyeuxia hieronymi. We used filters that attenuated specific wavelengths to generate three light treatments: full sunlight (FS), attenuation of UV (aUV), and attenuation of UV to blue-green wavelengths (aUV-BG). After 1.3 years, Deyeuxia litter from FS treatment decomposed 25.7 ± 1.8 % (mean ± s.e.), being 34% faster than aUV and aUV-BG which did not differ (p=0.001). In contrast, Poa litter from FS and aUV treatments lost 16.9% ± 0.5 of its mass, but did not differ from each other, and both lost 15% more than aUV-BG (p=0.0009). We observed similar patterns in litter chemistry, with faster mass loss observed in litter with greater carbohydrate accessibility. Our results suggest that direct and indirect effects of sunlight on Deyeuxia may be restricted to UV light, while visible light has a more marked effect on Poa. This highlights the importance of species composition for determining the integrated effects of photodegradation on C cycling in this mountain grassland ecosystem.