Variability in soil CO2 efflux across three distinct land cover types and in relation to environmental factors

Soil respiration, and consequently soil CO2 efflux, is a major component of the global carbon cycle and a major determinant of ecosystem carbon source or sink status, yet how environmental factors such as land cover type and soil characteristics contribute to soil respiration is still uncertain. Research has shown that soil CO2 efflux varies spatially due to differences in vegetation, rooting, and soil characteristics as well as other factors, and that the components of soil respiration (roots, rhizosphere, soil microbes, and organic matter decomposition) vary in sensitivity to temperature and moisture. This study compared soil CO2 efflux across three different land cover types in northern Virginia (mowed lawn, woodlot, and grassland) in relation to soil temperature, moisture and wind, as well as to soil characteristics including bulk density, porosity and pH, and root biomass and to vegetation characteristics, measured using plant area index and normalized difference vegetation index. Results show that soil CO2 efflux does vary across land cover type, which suggests that differences in dominant vegetation and land use should be included in carbon cycle modeling. Important environmental variables, soil temperature, soil moisture and wind speed, varied across land cover types but no relationships between flux and these variables were found except for a weak but highly significant relationship between soil CO2 efflux and soil temperature (R2= 0.2106). A weak negative relationship was also found between flux and plant area index. One conclusion that may explain these data is that belowground photosynthate supply, as root exudates from highly productive plants in mowed areas, causes these areas to produce much more CO2 from roots in the soil than the other land cover types, overshadowing the effects of other variables, but this was not measured in this study.