ABSTRACT Climate change alters rainfall patterns and increases temperatures, which disrupt soil processes, enhance CO 2 emissions, and reduce the capacity of soils to store carbon. Soil respiration, the CO 2 released into the atmosphere from the soil, is a vital process in the terrestrial carbon cycle. We performed a two‐year study investigating the seasonal variation of soil CO 2 efflux in two typical oak‐dominated Mediterranean ecosystems, a deciduous and a broadleaf evergreen one, as we lack sufficient information on this topic. To understand the drivers of soil respiration, we also monitored soil water content and temperature, as well as organic matter input by sampling litterfall and fine roots and by applying in parallel a litter and root exclusion approach. We found a 30%–54% higher soil CO 2 efflux in broadleaf evergreens vs. deciduous oaks, depending on the season. We also identified significant effects of all tested drivers on soil respiration. Soil water content controlled the dependency of soil respiration on temperature and resulted in the highest CO 2 emissions in spring, when these conditions were optimal. The high litterfall input and turnover rate in spring further supported the peak of CO 2 respired by broadleaf evergreens' soil in this period. On the contrary, low water availability limited soil respiration during summer in both ecosystems. The litter and fine root exclusion resulted in a 69.9% and 38.7% reduction in CO 2 efflux in spring, for deciduous and evergreen oaks, respectively, verifying the important contribution of these organic inputs to soil respiration. However, it led to overestimation of soil respiration in summer and in the second year of the study, probably due to water retention. We developed a polynomial regression model that predicts CO 2 efflux with soil temperature and water content as multipliers, and it is novel in including carbon fluxes of litterfall and fine root production as explanatory variables. The model predictions are good for broadleaf evergreen oaks ( R 2 = 0.64) and lower, but fair, for deciduous oaks ( R 2 = 0.48) and can efficiently illustrate how microclimate in combination with organic input and affects soil respiration. Our findings can improve our knowledge of soil CO 2 effluxes and their drivers in typical oak‐dominated Mediterranean ecosystems and support their climate‐adapted management.
Zacharoudi et al. (Sat,) studied this question.