Interannual precipitation controls on soil CO₂ fluxes in high elevation conifer and aspen forests

Long-term soil CO2 emission measurements are necessary for detecting trends and interannual variability in the terrestrial carbon cycle. Such records are becoming increasingly valuable as ecosystems experience altered environmental conditions associated with climate change. From 2013 to 2021, we continuously measured soil CO2 concentrations in the two dominant high elevation forest types, mixed conifer and aspen, in the upper Colorado River basin. We quantified the soil CO2 flux during the summer months, and found that the mean and total CO2 flux in both forests was related to the prior winter's snowfall and current summer's rainfall, with greater sensitivity to rainfall. We observed a decline in surface soil CO2 production, which we attributed to warming and a decrease in amount and frequency of summer rains. Our results demonstrate strong precipitation control on the soil CO2 flux in mountainous regions, a finding which has important implications for carbon cycling under future environmental change.