Soil respiration (Rs) is the second largest carbon dioxide (CO2) flux in terrestrial ecosystems, and it provides an average of 30-90% to ecosystem respiration (Reco). In semi-arid ecosystems, there is a considerable need to expand our knowledge on Rs trends. Chaparral, a semi-arid Mediterranean plant community in California, has the potential to act a sink, which is an essential ecosystem to mitigate climate change. However, Rs responses to meteorological variables remain uncertain in these regions and no studies have quantified how much Rs attributes to Reco in chaparral shrublands. Our study analyzed continuous field Rs data in chaparral shrublands, the effects of soil temperature (Ts) and soil water content (SWC), and its contribution to Reco.

Our study incorporated long-term Rs data collected by automated chambers and net ecosystem exchange (NEE) measurements collected by the eddy covariance technique from June 2020 to May 2021 in a chaparral stand in San Diego, California. The results suggest SWC was the strongest driver of Rs, whereas Ts was only a significant control when soil was wet, and temperatures were mild. Monthly Rs/Reco ratios, which described the contribution of Rs to Reco, were highest during the January and February, likely due to the reduced aboveground respiration. Whereas Rs/Reco ratios were lowest when SWC was the driest and Rs was reduced. The results from this study improve our understanding in Rs response to climatic conditions and emphasize the importance of Rs by quantifying its contribution to Reco in chaparral shrublands.