Seasonal Effects of Soil Temperature and Soil Water Content on Upscaled Soil Respiration and Its Contribution to Ecosystem Respiration in Chaparral Shrublands

Chaparral, a semi-arid Mediterranean plant community, has the potential to act as a sink, which is an essential ecosystem to mitigate climate change. However, soil respiration (Rs) responses to meteorological variables remain uncertain in these regions, and no studies have quantified how much Rs attributes to Reco in chaparral shrublands. This study identifies the effects of soil temperature (Ts) and soil water content (SWC) on upscaled Rs and its contribution to Reco (Rs/Reco) in chaparral shrublands in Southern California between 2020 and 2021. Hourly Rs and net ecosystem exchange (NEE) were collected by automated chambers and the eddy covariance technique, respectively. Due to high daily variability and gaps in our data, 5-day averages were calculated to understand the effects of meteorological on Rs and Rs/Reco. First, we proposed that SWC was the primary driver of Rs regardless of the season, while Ts effects were prominent when SWC was sufficient. Secondly, we hypothesized Rs/Reco to vary seasonally, particularly due to Rs contributing less under dry conditions. Our results showed SWC to have a strong significant effect on Rs throughout the year, whereas Ts was only a significant control when the soil was wet and Ts was below 20°C. Monthly Rs/Reco was highest during January and February, likely due to the reduced aboveground respiration. While Rs/Reco was lowest when the soil was the driest. These findings improve our understanding of Rs response to climatic conditions and emphasize the importance of estimating Rs/Reco in chaparral shrublands.