The response of plants to elevated CO : IV. Two deciduous-forest tree communities.

Tree saplings, two groups of three species from each of two deciduous tree communities, were grown in competition at three CO concentrations and two light levels. After one growing season, biomass was measured to assess the effect of CO on community structure, and nitrogen and phosphorus concentrations were measured for leaves, stems, and roots of all trees. Gas-exchange measurements were made on the same species grown under the same CO concentrations.Photosynthetic capacity (rate of photosynthesis at saturating CO and light) tended to decline as CO concentration increased, but differences were not statistically significant. Stomatal conductance declined significantly as CO increased. Nitrogen and phosphorus concentrations generally declined as CO increased, but there were some unexpected patterns in roots and stems. CO concentration did not significantly affect the overall growth of either community after one season, but the relative biomass of each species changed in a complex way, depending on CO light level, and community.