Plant Plant Interactions in Elevated CO₂ Environments

Abstract

Increasing atmospheric carbon dioxide concentrations present a novel resource condition for plant communities. In order to understand and predict how plant community structure and function may be altered in a high CO₂world, we need to understand how interactions among neighbouring plants within a community will alter the growth and reproduction of component species.

Because CO₂ is readily diffusible, plants have little influence on the CO₂ acquisition of their neighbours, except within particularly dense canopies. Thus, plants seldom compete directly for CO₂. Rather, CO₂ availability is likely to alter plant-plant interactions indirectly through its effects on plant growth and competition for other resources. As a consequence, competitive outcome under elevated CO₂ atmospheres within even simple systems is not easy to predict. For example, under some conditions, C₄ species in competitive assemblages have improved competitive ability relative to C₃ competitors as a result of CO₂ enrichment, contrary to expectations based on their photosynthetic pathways.

It is now clear that individually grown plants can differ substantially from those within mono- or multispecific stands in response to CO₂ enrichment. At present, our understanding of how stands of interacting plants modify the availability of CO₂ and other resources is incomplete. We urgently need information about how elevated CO₂ atmospheres influence stand formation and population dynamics, specifically with regard to the identities, numbers, sizes and reproductive fitnesses of individuals within single and multiple species stands, if we are to make multi-generational predictions concerning the fate of populations and communities in an elevated CO₂ world.