Air pollutants: Elevated carbon dioxide
The assessment of the potential combined effects of air pollutants and elevated atmospheric concentrations of carbon dioxide (CO2) on vegetation is of critical importance during the next decades. The interactive effects of these atmospheric compounds on crops, trees, and other types of vegetation have been shown. Existing evidence on such interactions is almost entirely restricted to CO2 and ozone (O3), the concentrations of which are increasing globally. Results from a number of studies indicate that elevated CO2 may reduce the adverse effects of O3 on plant growth and productivity, but the available information is inconsistent as several studies show that elevated CO2 did not ameliorate the negative effects of O3. The future interactions of elevated CO2 and enhanced atmospheric nitrogen (N) deposition are of concern in many ecosystem types with respect to carbon sequestration and biodiversity. The overall impact of climate change including elevated CO2 on future air pollutant effects are difficult to predict because of the largely uncertain influence and feedbacks of other growth variables such as plant genotype, soil water deficit, nutrient availability, or temperature.