Ecosystem studies often study soil CO2 flux as a function of environmental
factors, such as temperature, that affect respiration rates by changing the
rate of utilization of carbon substrates. These studies tend not to includ
e factors, such as photosynthesis, that affect the supply of carbon substra
tes to roots and root-associated processes. We examined the role of decreas
ed carbohydrate source on soil CO2 flux and root respiration in an annually
-burned grassland through manipulations of light intensity and removal of a
bove ground biomass. We also quantified the contribution of root respiratio
n to soil CO2 flux by measuring the respiration rates of excised roots. Two
days of shading caused a 40% reduction in soil CO2 flux, while clipping wa
s associated with a 19% reduction in soil CO2 flux. Both reductions were in
dependent of soil and air temperature at the time of measurement. The relat
ive decrease in soil CO2 flux observed in the clipping experiment was simil
ar in magnitude to an observed decrease in root respiration per gram of roo
t, linking decreased root activity and soil CO2 flux. From these experiment
s, we conclude that variation in factors that affect carbon availability to
roots can be important determinants of soil CO2 flux and should be include
d explicitly in studies that measure or model soil CO2 flux.