Does vegetation structure regulate the spatial structure of soil respiration within a sagebrush steppe ecosystem?

Patchy distribution of sagebrush (Artemisia tridentata), also known as 'islands of fertility' strongly modulates the biogeochemical dynamics of the sagebrush-steppe ecosystem. We tested the hypothesis that islands of fertility influence the spatial structure of soil respiration. We employed a spatial sampling design, which consisted of 0.5 m diameter plots placed in a repeating pattern within a grid of 12 m x 12 m. At each sample point, we measured soil respiration rates, aboveground vegetation cover, root biomass to 10 cm depth and distance and dimensions of the nearest shrub in four quadrants. Total aboveground leaf biomass was estimated from allometric relationships. We found that soil respiration was spatially autocorrelated with a range of 2.5-8.82 m in June and July in 2009. While soil temperature modulated the spatial pattern of soil respiration, the influence of islands of fertility was not as strong as expected. Spatial autocorrelation also highlights the importance of proper sampling design of point measurements of soil respiration and provides strong justification for including additional factors such as vegetation cover and aboveground leaf biomass in future mechanistic models of soil respiration.