Litter biomass as a driver of soil VOC fluxes in a Mediterranean forest

Abstract. Soil biogenic volatile organic compound (BVOC) emissions have been studied in different biomes, showing that their emissions are not negligible. However, previous studies have so far neglected the role of litter accumulation on soil BVOC fluxes, and most of them refer to coniferous and evergreen forests, while litter emissions from Mediterranean deciduous forests remain poorly explored. To fill these gaps, the present work aimed to study BVOC fluxes in a Mediterranean deciduous forest, with a particular attention to the relationship between soil BVOC fluxes and litter biomass accumulation on soils. Measurements were performed in southern France, in the downy oak (Quercus pubescens Willd.) forest of the Observatoire de Haute Provence (O3HP), during the late spring of 2023, using dynamic chambers coupled to an on-line PTR-ToF-MS. We investigated in-situ daily BVOC fluxes from soil alone and different litter biomasses mimicking low, current, high, and very high litter production, respectively, as both decreases and increases of litter accumulation are expected in the Mediterranean region under the current context of climate change and greening management policies. The results showed a high BVOC diversity with more than 135 emitted compounds. For a large majority of the measured compounds, the BVOC fluxes were negative, suggesting that soil (bare soil covered by litter) uptakes compounds through biochemical and/or physical processes. Some compounds, such as acetone, methanol or sesquiterpenes, increased with increasing litter biomass, suggesting the importance of considering litter accumulation when assessing soil BVOC emissions from Mediterranean deciduous forests. Microbial abundance was highlighted as a potential driver of this relation between litter biomass and VOC fluxes.