Using CO2 Efflux Rates to Indicate Below-Ground Growing Seasons by Land-use Treatment

Abstract

CO2 efflux rates are affected by vegetation type, temperature, and soil surface conditions, and serve as an indicator of the length of the below-ground biological and microbial growing season. This study determined the effect of three land-use treatments on CO2 efflux and growing season lengths in Southeast Virginia on two forested mineral soil wetlands. CO2 efflux, soil temperature, and soil moisture were measured 24 times in 18 months at plots representing forest, early successional field, and bare ground land-use treatments. CO2 efflux differed (p field > bare ground. CO2 efflux was higher in hardwood- than conifer-dominated forest and higher in bare ground plots that were not inundated. Appreciable CO2 efflux took place even once leaves had fallen off deciduous trees, and most of the CO2 efflux appeared to be from vegetation rather than microbial sources during that period. Variability in CO2 efflux was best described by the interaction between soil temperature and soil moisture (R2 = 0.32) (p < 0.05). The below-ground growing season indicated by appreciable CO2 efflux was similar to that indicated by soil temperatures above 5°C measured at 50 cm, the regulatory reference depth. The CO2 efflux growing season was 365 days in the forest but was 9–16 days shorter in the field and 21–78 days shorter in the bare ground land-use treatment plots. These data can be used to modify the regulatory growing season definition in forested thermic wetlands and to reflect the environmental variation caused by different land uses.