Combined effects of microenvironment and land use on C fluxes in a Mediterranean agro-silvopastoral system

Appropriate agroforestry practices might contribute to carbon sequestration and cope with climate change by modulating ecosystem services. It is known that land use change might affect soil-atmosphere carbon dioxide (CO 2 ) effluxes of agro-silvopastoral systems. However, little information is available at single microenvironment level. Across four years, fortnightly measurements of soil respiration were carried out at different microenvi­ronment (beneath tree cover vs open areas) and land use (native understorey vs its conversion into improved pasture) within a high-density evergreen cork oak forest of Sardinia (Italy). We also monitored aboveground dry matter yields and soil carbon stocks. Measurements revealed that the two investigated microenvironments widely differed for the amounts of photosynthetically active radiation and microclimatic traits such as soil water content, air humidity, soil and air temperature. High seasonal and inter-annual variability in soil respiration rateswas recorded (range 0.3-12.6 CO 2 ? mol m - 2 s -1 ) and the peak values were reached in the summer of the third year in the improved pasture beneath tree cover. The conversion of the native understorey into improved pasture beneath cork oak increased significantly the annual cumulative soil respiration for three consecutive years, reaching values of about 71, 36 and 100 t CO 2 ha - 1 yr - 1 , which were from 38 to 88 % higher than the remaining treatments. On average, heterotrophic component represented from 68-76% of soil respiration. An extreme drought event, which was emblematic of a climate change context, was experienced in the second year. Itcountered the increase in the heterotrophic component of soil respiration and minimized up to 20-fold the forage on offer from pasture swards. Based on measured CO 2 effluxes, the study demonstrated that the effects of the land use change at the microenvironment beneath tree cover were substantially unbalanced in terms of soil organic carbon stocks. Therefore, results suggest avoiding the soil mechanical disturbance beneath cork oak in the investigated ecosystem to reduce anthropogenic carbon fluxes to the atmosphere.