Fan et al., 2014. Modeling pulsed soil respiration in an African savanna ecosystem.

Fan, Z., Neff, J.C., Hanan, N.P., 2014. Modeling pulsed soil respiration in an African savanna ecosystem. Agricultural and Forest Meteorology 200, 282-292.

Abstract

Savannas cover 60% of the African continent and play an important role in the global carbon (C) emissions from fire and land use. To better characterize the biophysical controls over soil respiration in these settings, half-hourly observations of volumetric soil–water content, temperature, and the concentration of carbon dioxide (CO₂) at different soil depths were continually measured from 2005 to 2007 under trees (“sub-canopy”) and between trees (“inter-canopy”) in a savanna vegetation near Skukuza, Kruger National Park, South Africa. The measured soil climate and CO₂ concentration data were assimilated into a process-based model that estimates the CO₂ production and flux with coupled dynamics of dissolved organic C (DOC) and microbial biomass C. Our results show that temporal and spatial variations in CO₂ flux were strongly influenced by precipitation and vegetation cover, with two times greater CO₂ flux in the sub-canopy plots (∼2421 g CO₂ m⁻² yr⁻¹) than in the inter-canopy plots (∼1290 g CO₂ m⁻² yr⁻¹). Precipitation influenced soil respiration by changing soil temperature and moisture; however, our modeling analysis suggests that the pulsed response of soil respiration to precipitation events (known as “Birch effect”) is a key control on soil fluxes at this site. At this site, “Birch effect” contributed to approximately 50% and 65% of heterotrophic respiration or 20% and 39% of soil respiration in the sub-canopy and inter-canopy plots, respectively. These results suggest that pulsed response of respiration to precipitation events is an important component of the C cycle of savannas and should be considered in both measurement and modeling studies of carbon exchange in similar ecosystems.