Effect of Simulated Climate Change on Soil Respiration in a Mediterranean-Type Ecosystem: Rainfall and Habitat Type are More Important than Temperature or the Soil Carbon Pool

Soil respiration (R _S) is known to be highly sensitive to different environmental factors, such as temperature, precipitation, and the soil carbon (C) pool. Thus, the scenario of global change expected for the coming decades might imply important consequences for R _S dynamics. In addition, all of these factors may have an interactive effect, and the consequences are often confounded. We performed a field experiment to analyze the effect of soil moisture and habitat type on R _S in a Mediterranean-type ecosystem by simulating three possible climate scenarios differing in the precipitation amount during summer (drier, wetter, and current precipitation pattern) in the main successional habitats in the area (forest, shrubland, and open habitat). We also considered other factors that would affect R _S, such as the soil C pool and microbial biomass. By the use of structural-equation modeling (SEM), we disentangled the interactive effects of the different factors affecting R _S. A higher simulated precipitation boosted R _S for the different habitats across the sampling period (14.6% higher respect to control), whereas the more severe simulated drought reduced it (19.2% lower respect to control), a trend that was similar at the daily scale. Temperature had, by contrast, scant effects on R _S. The SEM analysis revealed a positive effect of moisture and canopy cover on R _S, whereas the effect of temperature was weaker and negative. Soil C pool and microbial biomass did not affect R _S. We conclude that the precipitation changes expected for the coming decades would play a more important role in controlling R _S than would other factors. Thus, the projected changes in the precipitation pattern may have much more profound direct effects on R _S than will the projected temperature increases.