Impact of reduced rainfall on soil nutrient availability in Mediterranean forests: Underscoring the importance of spatiotemporal variability

Mediterranean forests face increasing drought risks under climate change, potentially altering soil nutrient dynamics and thus forest productivity and resilience. Yet, the impacts of climate-driven drought on belowground processes remain poorly understood. This study assessed how reduced rainfall, as predicted by climate models, influences short-term soil nitrogen (N) and phosphorus (P) availability, emphasizing spatial and temporal variability. We conducted a rainfall exclusion field experiment using 2,752 ion exchange membranes (IEMs) over two years to seasonally monitor inorganic N and P availability at two topsoil depths in two mixed Mediterranean forests. These forests differed in dominant tree species - closed forest of Quercus suber and Quercus canariensis and open woodland of Quercus suber and Olea europaea - and exhibited substantial fine-scale soil texture variability. Rainfall exclusion generally increased N and P availability, indicating that reduced soil moisture primarily limits plant nutrient uptake rather than microbial activity. Responses were more pronounced for N than for P, in spring and fall, and during the driest year, anticipating potential nutrient decoupling in future drier scenarios. Soil texture, depth, and dominant tree species modulated nutrient responses, with more pronounced effects in sandier soils, at 25 cm depth, and under Quercus spp. Our study underscores the robust effects of climate change-driven drought on soil nutrient availability in Mediterranean forests, but also the need to account for the spatial and temporal variability of these effects. Without this comprehensive approach, predictions of the fate of these forests under climate change scenarios will remain constrained