Causes of spatial and temporal variation in soil respiration along a Rocky Mountain riparian-meadow ecotone

We investigated factors leading to spatial and temporal variation in soil respiration in a Rocky Mountain meadow surrounded by riparian trees.  Soil carbon dioxide profiles, surface fluxes, dissolved organic carbon, and microbial biomass carbon were measured along transects from the perimeter trees towards the center of the meadow at several times during the 2006 growing season.  A diffusion model was used to estimate depths of greatest CO₂ production along the transect over the season.   Soil respiration peaked at about 7 μmoles/m²/s for all transect positions in June at the height of the growing season, and again in summer after a rain event that reduced soil moisture stress.  Root activity appeared to be the dominant control over variability in spring and summer soil respiration.  Microbial biomass carbon and dissolved organic carbon increased with proximity to trees to roughly 25 and 100 μmolesC/gram dry soil, respectively, but did not show a strong relationship with soil respiration during the active growing season.  Position on the tree-meadow transect was apparently most important during the period between senescence of the meadow vegetation and before dormancy of the riparian trees.  Our data support the conclusion that soil respiration is affected by vegetation type and phenology directly via root respiration, as well as differences in soil carbon accumulation.