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.

Mangrove forests are among the most productive ecosystems in the world. These tropical and subtropical coastal forests provide a wide array of ecosystem services, including the ability to sequester and store large amounts of ‘blue carbon’. Given rising concerns over anthropogenic carbon dioxide (CO2) emissions, mangrove forests have been increasingly recognized for their potential in climate change mitigation programs. However, their productivity differs considerably across environments, making it difficult to estimate carbon sequestration potentials at regional scales. Additionally, most research has focused in humid and tropical latitudes, with limited studies in arid and semi-arid regions. A semi-arid mangrove forest in Magdalena Bay, Baja California Sur, Mexico was studied to quantify the average net ecosystem exchange (NEE), determine the annual carbon (C) budget and the environmental controls driving those fluxes. Measurements were taken during 2012-2013 using the eddy covariance technique, with a daily mean NEE of -2.25 +/- 0.4 g C m-2 d-1 and annual carbon uptake of 894 g C m-2 y-1. Daily variations in NEE were primarily regulated by light, but air temperature and vapor pressure deficit were strong seasonal drivers. Our research demonstrates that despite the harsh and arid climate, the mangroves of Magdalena Bay were nearly as productive as mangroves found in tropical and subtropical climates. These results broaden understanding of the ecosystem services of one of the largest mangrove ecosystems in the Baja California peninsula, and highlight the potential role of arid mangrove ecosystems for C accounting, management and mitigation plans for the region.