Determinants of growing season soil CO2 flux in a Minnesota grassland

Soil CO2 flux was measured across 947 plots at 7 experimental grassland sites at the Cedar Creek Natural History Area in order to determine the relationships between soil CO2 flux and environmental factors, living plant biomass, and soil C and N. Soil CO2 flux increased as the day progressed, and was positively related to aboveground biomass, belowground biomass, and soil % C. However, most of the variation in soil CO2 flux explained by a multiple regression model (r 2 = 0.55) was attributed to the different experimental sites (61%). Soil CO2 flux increased with increasing aboveground plant biomass (explaining 16% of the model variation), belowground plant biomass (12%), and soil C and C:N ratio (6%). The length of time between aboveground biomass in a plot was clipped and soil CO2 flux varied among plots. Soil CO2 flux declined with increased time since clipping, supporting the idea that recently fixed carbon is a significant component of soil CO2 flux. Soil CO2 flux did not follow standard Q10 relationships. Over a 20 °C temperature range, soil CO2 flux tended to be lower in warmer plots. More work is necessary to understand what factors explain the large differences that were seen among experimental sites in soil CO2 flux that could not be explained by biomass or soil properties.