Summer sunlight impacts carbon turnover in a spatially heterogeneous Patagonian woodland

Purpose We evaluated the importance of dry season (summer) sunlight on carbon (C) turnover in a Mediterranean-type climate ecosystem in the context of spatially heterogenous distribution of vegetation. Methods We manipulated summer sunlight exposure of litter and soil at the ecosystem scale in a natural Patagonian woodland over two years and evaluated its effect on C turnover in litter and surface soil. We measured decomposition of standing dead litter of dominant grass and shrub species, changes in labile C pools in soil microsites with and without plant litter, and potential enzyme activity of litter and both soil microsites, evaluating seasonal and legacy effects of summer sunlight exposure. Results Summer sunlight exposure significantly increased standing litter decomposition for both shrub and grass litter (p < 0.05). Additionally, summer sunlight significantly increased labile carbohydrate availability (saccharification) and potential microbial enzymatic activity of grass (but not shrub) litter. Interestingly, summer sunlight exposure also had effects on soil, reducing by 50% labile organic C while stimulating potential extracellular enzyme activity in both soil microsites, with and without plant litter. Conclusion Summer sunlight accelerates C loss from standing litter and soil consistently across patches of heterogeneously distributed vegetation. In addition, sunlight exposure demonstrated carryover effects on the acceleration of grass litter decay in the following rainy season, when sunlight increased decomposition five times more than in the dry season. These results suggest that summer sunlight is an important and lasting control of C turnover at the ecosystem scale even in seasonally and spatially heterogenous ecosystems.