Tracking rain events impact on soil and plant leaf water content over time

Abstract Background and aims In semi-arid Mediterranean ecosystems, limited water availability impacts plant performance. This study explores water movement from rainfall through soil to plants, hypothesizing that (i) vegetation buffers water stress by allowing more (and smaller) rain events to percolate deeper, and (ii) plant species' physiognomy conditions their dependence on soil moisture, with larger or deep-rooted species having their leaf water content less coupled with the temporal variation in soil moisture. Methods We contextualize abiotic stress by analyzing 66 years of rainfall data, track rain events and vegetation influence on soil moisture with soil data loggers and a field-based pluviometer over a year, and assessed soil-leaf water coupling by measuring foliar water content of 177 individuals of nine plant species over one growing season. Results The mean annual rainfall is ~ 366 mm, with dry years occurring more frequently (every 4.3 ± 0.9 years) than wet ones (every 7.4 ± 0.9 years). Summers have the smallest (8.7 ± 0.7 mm) and shortest (1.5 ± 0.05 days) rain events, with the largest lags with no rain 15.3 ± 0.9 days (maximum 112 days). Only rainfall ≥ 4 mm increased shallow soil moisture, and ≥ 6 mm increased deep soil moisture, and last 5–6 days to desiccate. Vegetation allows more (and smaller) rain events to percolate into deeper soil, maintaining higher moisture between events, especially in deep soil. Finally, foliar measurements showed that leaf water content across time is more correlated with deep than shallow soil moisture, with larger species (or with more developed root systems, e.g. Stipa tennacissima,Teucrium libanitis), being less coupled with temporal soil moisture. Conclusion This study deepens our understanding of water movement in semi-arid Mediterranean systems connecting rainfall patterns to soil moisture and plant responses over time. This understanding will allow more accurate predictions of how rainfall variability may impact plant communities and ecosystem functioning in semi-arid ecosystems.