Modelling the effects of climate factors on soil respiration across Mediterranean ecosystems

Soil CO2 emissions are critical for climate change modelling. Although there is a consensus about the linear or exponential relations between soil respiration and climate factors, some works have shown this abstraction to be invalid under arid and semiarid conditions, especially those in the Mediterranean-type climate. In this work, the latest empirical models were tested on previously published data from three sites representing different agricultural areas under Mediterranean conditions and contrasting soil uses. Soil heterotrophic respiration, soil temperature and volumetric water content were monitored on average every two weeks in each site over at least one year. With the findings in the three sites in Spain and Italy, it can be concluded that soil temperature was the main driver of soil respiration, as in temperate sites. However, owing to the extreme variability in climate variables, soil moisture modulates the response of soil respiration to temperature changes, and is thus another key for modelling soil respiration in Mediterranean conditions. Irrigation practices with high water inputs also substantially modify the soil respiration pattern, causing it to become similar to temperate soils. Finally, the results indicate that annual extreme values may be especially relevant in the relationship between climate variables and soil CO2 emissions.