The impact of ozone and other limitations on the crop productivity response to CO2

Numerous studies indicate that increasing atmospheric CO2 concentrations might enhance the productivity of current cropping systems. However, it appears that this productivity benefit may, in some cases, be the result of amelioration of the effects of co-occurring stresses by elevated CO2. In a series of experiments conducted in open-top field chambers over a period of 6 years using cotton, rice, soybean, and wheat, it was demonstrated that the crop yield response to doubled CO2 concentration was highly dependent on the co-occurring concentration of the air pollutant O3. Yield responses to elevated CO2 ranged from losses of 26% to increases up to about 40% in charcoal filtered air. However, plants grown under O3 stress showed yield increases in response to CO2 of up to 140%. Increased vegetative biomass in elevated CO2 treatments was consistently observed, but this extra biomass was not always translated into increased economic yield. Elevated CO2 concentrations did, however, ameliorate the average 27% yield suppression caused by pollutant O3, primarily through reducing leaf conductance and limiting the O3 flux into leaves. The amelioration of O3 damage and consequent higher yields would appear to be a direct stimulation of productivity by CO2 if there was no recognition of extant O3 pollution during the experiment. The same misperception might arise in the case of unrecognized or unmonitored water or nutrient stress conditions. We conclude that the effects of background levels of air pollutants and other environmental stresses should be included in the calculations used to predict crop productivity in a future atmosphere containing higher CO2 concentrations.

Duke Scholars

Author Chantal D. Reid Environmental Sciences and Policy