Wetting-drying cycles influence on soil respiration in two Mediterranean ecosystems

- Soil respiration increased during wetting events and decreased during drying events.
- Annual trends in soil respiration and nutrients were determined by local conditions.
- The initial water status of the wetting or drying event had a key effect on soil respiration.
- The length of the drought period prior to rewetting had no effect on soil respiration.
- Soil temperature had a secondary role on determining soil respiration.

This study assesses which factors are involved in the soil respiration (Sr) response to wetting-drying cycles in two Mediterranean ecosystems. We analysed Sr, mineral nitrogen, ion-exchange resin mineral nitrogen, and phosphate levels at weekly intervals over one year in two Mediterranean ecosystems with contrasting characteristics: a pine forest with high levels of organic matter and nutrients and a shrubland with low carbon and nutrients availability. Higher Sr was detected in the pine forest (0.12-0.76 g CO2 m−2 hour−1) than in the shrubland (0.04-0.67 g CO2 m−2 hour−1). For both sites, Sr increased during wet periods and decreased during dry periods. Compared with Sr in the pine forest, the trend observed for resin mineral nitrogen was the opposite. No pattern was observed for resin mineral nitrogen at the shrubland site, or for mineral nitrogen or phosphate at either site. The initial water status of the wetting-drying cycles determined the Sr response, whereas the length of the drought period before the rewetting event had no effect. The impact of the initial soil water content on Sr played a crucial role when the wetting-drying events occur in a dry soil, having a secondary role in wet soils. Finally, soil water status drove Sr during the growing season in both ecosystems; however, soil temperature had no effect on CO2 efflux. In a changing world with projections of intensifying wetting-drying events, our results highlight the influence of soil water status on respiration rates, especially when these events occur in a dry soil.