Spatial and temporal controls of soil respiration rate in a high-elevation, subalpine forest

We examined soil respiration to determine what measurable environmental variables can be used to predict variation in soil respiration rates, spatially and temporally, at a high-elevation, mixed conifer, subalpine forest site at the Niwot Ridge Ameriflux Site in Colorado. For three summers, soil respiration rates were measured using soil collars and a portable gas-exchange system. Transects of the collars were established to ensure spatial characterization of the litter-repleted areas beneath tree crowns and the litter-depleted open spaces between tree crowns. Soil temperature and soil moisture were both identified as important drivers of soil respiration rate, but were found to confound each other and to function as primary controls at different scales. Soil temperature represents a primary control seasonally, and soil moisture represents a primary control interannually. Spatially, organic layer thickness, ammonium concentration, water content, and the microbial and soil soluble carbon pools were found to predict variation from point to point. Soil microbial biomass strongly correlated to soil respiration rate, whereas root biomass was identified as a weak predictor of respiration rate and only when controlling for other variables. Spatial variation in soil respiration rate is highly determined by the depth of the soil organic horizon, which in this ecosystem varies predictably according to distance from trees. The conclusions that can be drawn from the study provide the foundation for the development of future models of soil respiration driven by fundamental variables of the climate and soil microenvironment.