Spatial variability of soil respiration in a 64-year-old longleaf pine forest

The objectives of this study were to determine the spatial structure of soil respiration (Rs) in a naturally-regenerated longleaf pine forest and to assess the ecological factors affecting the spatial variability in Rs. Soil respiration, soil temperature (Ts), and soil moisture were repeatedly measured over 6 days in summer 2012 in 3 semi-independent plots. Edaphic, forest floor, and root variables were measured. Diameters of 338 trees were mapped. Spatial analysis and regression were applied. Soil respiration was spatially autocorrelated across plots (66-92 m), but not within plots (6-34 m). Spatial distributions of Rs were relatively stable from morning through early evening and were decoupled from temporal variation of Ts. Ecological covariates (e.g., soil moisture, bulk density and carbon, litter mass, understory cover, roots, nearby trees) related to the spatial variability in Rs; however, models varied between plots. This study shows the importance of stationary plant and soil factors in determining the spatial, temperature-independent distribution of Rs in a heterogeneous forest. We suggest the need for a better understanding of the complex interactions between the heterotrophic, autotrophic, and physical processes driving Rs in order to better model forest carbon budgets.