Climate Change and Grasslands: Ecosystem-Level Responses to Elevated Carbon Dioxide

Elevated CO2 is the major greenhouse gas associated with global climate change. The impact of increasing atmospheric CO2 on grassland ecosystems has been studied little. Studies with single plants or populations in controlled environments have provided knowledge of the mechanisms involved in plant response to elevated CO21 but without ecosystem-level studies over an extended period, we will be unable to make any valid predictions. Primary production of grassland ecosystems under elevated CO2 will likely increase, with the greatest increase coming with C3-dominated plant communities, or plant communities that are .subjected to frequent drought stress. Increased nitrogen-use efficiency and reduced nitrogen requirement under elevated CO2 may allow the increased primary production to persist. However, reduced quality of the litter entering the detritnl food chain may slow nutrient cycling and feedback on primary production. Leaves of plants exposed lo elevated CO2 have reduced nitrogen concentration and increased fibre content, which may decrease intake of ruminants and increase intake of insects. It is extremely difficult to predict plant community species composition changes, but indications are that elevated CO2 will not be directly responsible for changes in species composition. Other scarce resources usually control competitive relationships among plants in natural grassland ecosystems.