Spatial and temporal variability of soil CO2 efflux in three proximate temperate forest ecosystems

The magnitude of CO2 flux from soil (F-soil) varies with primary productivity and environmental drivers of respiration, soil temperature (T-soil) and moisture, all of which vary temporally and spatially. To quantify the sources of Fson variability, we first compared F-soil of three proximate forests within 30 km of one another, ranging in age, composition, soil, and environment and, thus, productivity. We collected data with automated soil respiration chambers during a 10-year period in a mid-rotation Pinus taeda plantation (PP), for three-years in a mature P. taeda stand (OP), and for five-years in a mature, mixed-species hardwood (HW) stand; PP and HW were on clay-loam soil and OP on a sandy soil. Among stands, Fsoil sensitivity to T-soil was lowest in OP and highest in PP, reflected in mean annual F-soil (+/- standard deviation) of 1033 +/- 226 (OP), 1206 +/- 99(11W), and 1383 +/- 152 (PP) g Cm-2; both F-soil sensitivity to T5011 and annual F-soil increased with leaf litterfall. For the second portion of our study, we established an additional three plots at PP for a six-year period to examine within-stand variability. Within PP, sensitivity of F-soil to T-soil was similar, yet higher leaf area was correlated with a combination of lower soil temperature and belowground carbon flux, resulting in lower F-soil. Temporally, diurnal to seasonal F-soil followed T-soil whereas annual values were driven by soil moisture. Spatially, among the three stands F-soil increased with leaf production, whereas within a stand (PP) F-soil decreased with increasing leaf production. (C) 2012 Elsevier B.V. All rights reserved.