Influence of Elevated Atmospheric CO₂ Concentrations on Plant Nutrition

Abstract

The rising levels of atmospheric CO₂ are likely to increase biomass production of C₃ species in both natural and managed ecosystems because photosynthetic rates will be higher. The greatest absolute increase in productivity will occur when nitrogen and phosphorus availability in the soil is high. Low nitrogen does not preclude a growth response to high CO₂, whereas some C₃ species fail to respond to high CO₂ when phosphorus is low, possibly because insufficient phosphorus is available to maintain maximum photosynthetic activity at high CO₂.

C₃ plants response to high CO₂ because the flux of carbon through the photoreductive cycle is increased and photorespiration is suppressed. This change in metabolism appears to alter the foliar nutrient concentration required to promote maximum productivity (critical concentration). Higher phosphorus concentrations are needed at elevated CO₂, whereas the nitrogen requirement is reduced by CO₂ enrichment. Since critical concentrations are used to evaluate nutrient status of crop and forest species and to manage fertiliser programs, they will need reassessing as the atmospheric CO₂ concentration rises. Another consequence of the altered nutrient requirement at high CO₂ is that the nitrogen concentrations of foliage, roots and grain are consistently lower in plants grown at elevated CO₂, irrespective of availability of nitrogen in the soil. In natural ecosystems, the lower nitrogen to carbon ratio of the litter may alter rates of nutrient cycling. For farmers, the rising CO₂ concentrations could cause reductions in grain nitrogen, and therefore protein content. This could have important implications for baking quality of hard wheats as well as affecting the nutrient value of grain such as rice.