Global change is altering the timing and magnitude of precipitation (snow and rain) in the western US mountains. Snowmelt is occurring earlier in the spring, and in most regions, snowpack is declining. The monsoon rains are arriving later in the summer and are more sporadic than in previous decades. These changes decrease water available to plants and soil microbes during the summer months, and thus have implications for belowground processes, such as plant rooting, soil microbial activity, and overall belowground carbon cycling.
The objective of this project is to quantify how snow and rain water inputs influence the CO2 coming from the soil surface (soil CO2 flux), and its plant and microbial sources, with new field measurements along an elevational transect on Snodgrass Mountain, near Crested Butte, Colorado. These sites have been chosen to differ in snowpack and water table depth, and will include both deciduous (aspen) and evergreen (spruce/fir) forest types. Using automated measurements of soil CO2 concentrations, we will quantify soil CO2 flux, and the vertical CO2 production within the soil profile at each site. Isotope (radiocarbon, 14C) measurements will be conducted to determine how much of the CO2 emitted from the soil surface is coming from plant respiration (root metabolism) versus microbial respiration (decomposition of soil organic matter) sources. Supporting data on plant phenology (PhenoCams) and microbial dynamics will be used to provide context for the observed variation in respiration sources. This project is funded by DOE.