Spatial and Temporal Relationships of Soil Respiration in the Big Chico Creek Ecological Reserve.

Regional carbon budgets account for soil based carbon fluxes, which are primarily from autotrophic and heterotrophic soil organisms.  Soil surface carbon flux respiration (SR) varies spatially because of soil physical and biological properties, which includes vegetative structure and biomass production.  The Sierra foothill region predominantly consists of Blue oak (Quercus douglasii) woodlands separated by open meadows.  SR could vary spatially given the greater above\below ground biomass in trees communities versus grass meadows.  Goals for this study were to determine spatial and temporal relationships among SR, soil moisture (SM %) and soil temperature (Ts), within the Big Chico Creek Ecological Reserve.  At three sites, transects traversed two tree-less grass meadows separated by transition tree zones.  Five and three plots were located every 20m within the meadows and transition zones, respectively.  Three SR measurements (PPSystems CIRAS-1 IRGA), one Ts (10cm) and SM% per plot were measured weekly (Feb-May).  Additional measurements determined the effect of distance from trees on SR.  Results indicated small spatial\temporal differences in SR among sites and vegetative type within sites due mostly to SM%; However, although SM% determined the magnitude of SR, it was Ts that directly influenced SR.  Below 10 ^oC and above 16 ^oC SR was significantly reduced (< 3 umol CO₂ m^-2 s^-1), but within the 6 ^oC range SR was greater than 10 umol CO₂ m^-2 s^-1.  Results suggest a bimodal annual SR maximum, primarily dependent on Ts and only secondarily on SM%.  Effect of distance from tree was similar; However SR declined steadily with increasing distance from the tree base, regardless of seasonal based changes.