Interactions Among Abiotic Drivers, Disturbance and Gross Ecosystem Carbon Exchange on Soil Respiration from Subtropical Pine Savannas

Globally, soil CO₂ efflux rates (F s) have been linked to changes in soil water content (SWC), rainfall and temperature and/or productivity. However, within an ecosystem, F s can vary based on site structure and function, which can be affected by a combination of abiotic and biotic factors. This becomes particularly important when an ecosystem is faced with disturbances, such as drought or fire. Sitespecific compensatory responses to disturbances may therefore alter C mineralization, as well as root respiration. Hence, single location F s estimates may not be a representative for ecosystems across their distributional ranges. We conducted a 6-year study along an edaphic moisture gradient of longleaf pine ecosystems that were maintained with prescribed fire, using eddy covariance and soil respiration measurements to address how F s varies with changes in ecosystem structure and function, as well as disturbances. Lower air temperatures (T air) decreased F s at all sites, but that response was also affected by productivity and SWC. Productivity significantly altered F s rates at all sites, especially when we accounted for changes in temperature and SWC. Plant regrowth post-fire temporarily increased F s (10–40%), whereas drought reduced F s at all sites. Our results show that site productivity, F s and the degree to which ecosystems adapt to climate variations and disturbance can be site specific. Hence, model forecasting of carbon dynamics would strongly benefit from multi-location measurements of F s across the distributional range of an ecosystem.