Soil CO2 Flux – Separating Substrate and Microclimate Effects in Managed and Native Ecosystems.

Soil CO₂ fluxes are an integrated response to the numerous site factors that affect organic matter decomposition and plant root respiration.  Separating the relative effects of organic substrate/decomposer community characteristics from soil temperature and moisture regimes enriches the interpretation of potential land use change effects on soil CO₂ fluxes.  Soil CO₂ flux was measured during the 2007 growing season in adjacent old growth forest and crop (corn) ecosystems near Sant Agostino, Italy and 4 yr-old reconstructed prairie and no-till crop (soybean) ecosystems near Prairie City, Iowa using a closed-chamber apparatus.  Soil CO₂ fluxes averaged 0.83 and 0.74 g cm^-2 hr^-1 for the forest and crop sites, respectively.  The fluxes were not significantly different even though the standard error was double for the crop site which also had on average 35% higher soil temperature (7.1° C) and 35% lower water content (0.07 m³ m^-3) than the forest site.  Fluxes for the prairie and no-till crop sites averaged 0.62 and 0.67 g cm^-2 hr^-1, respectively and were also not significantly different.  Again, the standard error was much greater (0.030 vs. 0.017) and the soil temperature was on average 15% warmer (3.0° C) and soil water content 10% lower (0.03 m³ m^-3) at the crop site.  After three measurement cycles at Sant Agostino, three of the soil collars from each ecosystem were transplanted to the other ecosystem and followed by three more measurement cycles.  Although fluxes for crop field soil transplanted to the forest decreased by an average of 0.08 g cm^-2 hr^-1 (16%) and  fluxes for forest soil transplanted to the crop field decreased by 0.35 g cm^-2 hr^-1 (40%), these changes were confounded by lack of rain which resulted in lower control soil fluxes as well.  Measurements at the prairie and no-till crop site in 2008 will further evaluate the utility of the transplant technique.