Moisture, temperature and respiration of two soil classes under pasture and tropical dry forest in the semiarid Brazilian region

Soil respiration (Rs), or soil CO2 efflux, is the largest carbon flux from ecosystems to the atmosphere; it is an order of magnitude greater than that released by human activity, and is a key process in CO2 atmospheric accumulation and climate change. Due to its importance, many studies have investigated respiration in different ecosystems, with studies in tropical dry areas being more scarce. We measured the effects of soil temperature and moisture on respiration from Regosols and Luvisols under pasture and native deciduous forests in the Brazilian Northeast semiarid region. Respiration had a direct relationship with soil moisture and an inverse relationship with temperature in both soil classes and land covers. Respiration was higher under the forest than under the pasture (9.0 and 4.8 Mg C ha-1 y-1) in both wet and dry seasons, probably due to higher biomass incorporation and higher root respiration, but it did not differ between soil classes. These respirations corresponded to high proportions of the soil C contents in the 0-10 cm superficial layer (46.2% in Caatinga and 36.7% in pasture). In the Brazilian semiarid region, soil respiration was controlled by soil moisture (positively) and temperature (negatively), both of which were affected by land-use changes.