ANOMALOUS RESPONSES OF PLANTS TO CO2 ENRICHMENT

A number of unexplained responses of plants to CO2 enrichment have been observed. These anomalies can be explained on the basis of growth analysis of whole plants. Some plants may fail to respond to enrichment because they are long-lived and have conservative growth responses or come from impoverished habitats. Apparent (but not real) acclimation to CO2 enrichment might be observed if only part of the growth curve over the life of a perennial is studied. The apparent increased efficiency of nitrogen use may merely be an increase in storage of nonstructural carbohydrate. A model analysis of these effects is presented. Discrepancies among species in relative responses of different plant parts are argued to be largely a function of where the plant typically stores nonstructural carbohydrates, which itself is a function of plant growth stage. Thus, a closer consideration of plant growth strategies and growth partitioning is needed to properly interpret results of CO2 enrichment studies.