Variation in Soil Respiration Across an Alpine Soil Moisture and Vegetation Community Gradient at Niwot Ridge, Colorado

Abstract:

The alpine tundra is a mosaic of comingled vegetation communities that vary predominantly as a function of landscape position, micro-scale topography, subsurface permeability, and resultant soil moisture availability. We characterized the spatio-temporal variability of soil respiration from 17 alpine tundra sites across an irregular soil moisture gradient within the footprint of ongoing eddy covariance measurements over the 2011 (wet year) and 2012 (dry year) growing seasons. We then used a soil moisture threshold as a proxy to separate the sites into fellfield, dry/moist meadow, and wet meadow tundra vegetation communities. Soil moisture and soil respiration were significantly correlated across all communities (p << 0.001), but increasing soil moisture invoked a bidirectional response from fellfield and dry/moist meadow communities (directly proportional) relative to wet meadow communities (inversely proportional). Soil temperature and soil respiration were not significantly correlated. Linearly interpolating between sampling dates, the cumulative soil respiration flux over the two growing seasons ranged from 595 to 3177 g CO₂ m^-2, and median fluxes were 1114, 1679, and 1400 g CO₂ m^-2 for fellfield, dry/moist meadow, and wet meadow sites, respectively. Ecosystem respiration from nighttime eddy covariance measurements was 618 g CO₂ m^-2 over the same period, suggesting that soil respiration fluxes from very dry fellfield tundra disproportionately influenced the eddy covariance data. Overall, cumulative soil respiration was 50% greater in the wet year (2011) relative to the dry year (2012); therefore increased precipitation has the potential to increase soil respiration from alpine tundra as a whole.