Breathing Soils: Implications of Small-Scale Spatial Variations in Seasonal Soil CO­­2 Respiration in a Rocky Mountain Subalpine Meadow

Plant root and soil organism respiration of CO₂ is one of the largest natural fluxes of carbon from the land surface to the atmosphere. This flux is understood to be sensitive to changes in temperature and in the timing and amount of precipitation via effects on soil moisture, temperature, and microbial and plant primary productivity. Both laboratory incubations and field-collected point measurements have shown that soil respiration responds to changes in precipitation and temperature. However, when attempting to quantify landscape fluxes, there have been limited studies suggesting these relationships hold over larger spatial domains (km-scale), where competing factors such as plant and microbial species turnover may interact with the relationships observed at smaller scales. To determine how CO₂ fluxes vary across scales, we examined the relationship between soil CO­₂ respiration and landscape metrics of soil moisture across a subalpine meadow in the Colorado Rockies (East River, CO) from late May to August. To quantify hillslope-scale spatial variation in soil moisture and respiration across the growing season, we measured surface soil moisture and CO₂ respiration rate at spatial distances of 0.5-40 m in a grid of 74 points across a 625 m² area at four discrete time points. The magnitude of variability in both soil moisture and respiration slightly increased later in the growing season, corresponding with precipitation events. We found that soil respiration was not well correlated with soil moisture at the hillslope scale. Additionally, LiDAR-derived topographic wetness index (TWI) was not correlated with soil moisture or soil respiration, indicating the metric did not capture the key drivers for either property at our site. The limited correlations between soil respiration and topographic indices present challenges for extrapolating meter-scale measurements of soil moisture, temperature, and respiration to the catchment scale (km).