In the past several years we have systematically investigated changes in the size of potential sinks for the 'excess' carbon assimilated by the C 3 plant community at elevated CO₂ . We found an increase in the root biomass pool and winter respiration, but there is still a large imbalance that cannot be explained (Table Below).

One possibility that can now be dismissed is export of dissolved carbon from the chambers, as explained in the next section. In the description of proposed research, we provide a rationale for perhaps the last possible sink to be investigated, an increase in the soil organic matter content that manifests as a rise in the soil surface elevation. Although we measured soil carbon content at the site, we did not account for the possibility that the soil surface has risen due to higher shoot and root productivity.