Results are indefinite, but do indicate that changes in the strength of the biological pump cannot alone have been responsible. W.H. Schlesinger, ibid. Comment on the importance of soil carbonate in estimates of the global budget. Eddy correlation measurements of CO 2 flux combined with simulated data show that CO 2 exchange between the experimental ecosystem and the atmosphere is highly variable. Drought, a frequent occurrence in the region, can change the ecosystem from a source to a sink for CO 2 .
Results suggest the importance of below-ground biomass in estimating net primary productivity.
Botany, Iowa State Univ. Reviews measured rates of soil respiration from terrestrial and wetland ecosystems to define the annual global CO 2 flux from soils, to identify uncertainties, and to investigate influences on soil respiration rates. Evaluates human impacts on respiration rates, particularly land use, soil fertilization, irrigation and drainage, and climate changes. Increased soil respiration with global warming is likely to provide a positive feedback to the greenhouse effect. S.J. Schaefer et al., Geochim.