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Effects of Elevated CO2 and Ozone on the Nitrogen Acquisition and Growth of Peanuts

Reference
Tu, C., Booker, F.L., Burkey, K.O. and Hu, S. 2009. Elevated atmospheric carbon dioxide and O3 differentially alter nitrogen acquisition in peanut. Crop Science 49: 1827-1836.
Tu et al. (2009) grew peanut (Arachis hypogaea L.) plants from seed to maturity out-of-doors near Raleigh, North Carolina (USA) in open-top chambers under adequately watered and fertilized conditions, while exposing the plants to (1) charcoal-filtered air, which was thus ozone-free, (2) ambient air of unaltered ozone (O3) concentration, and (3) air containing 1.6 times the ambient O3 concentration, all of which O3 treatments were exposed to air of 376, 550 and 730 ppm CO2, during which time the researchers made many different plant physiological measurements, and at the end of which period they harvested the crop and measured its final steam, leaf and pod biomass.

Tu et al. report that "elevated CO2 generally increased biomass production while O3 suppressed it, and CO2 ameliorated the O3 effect." In terms of the season-long mean of midday net photosynthesis, for example, the 94% increase in the air's CO2 concentration experienced in going from the lowest to the highest CO2 treatment resulted in a 25% increase in net photosynthesis in the charcoal-filtered air, a 50% increase in the non-filtered air, and a 104% increase in the ozone-polluted air; while in terms of the final aboveground biomass produced, the corresponding CO2-induced increases were 10%, 41% and 105%.

On the other hand, the four researchers found that "at mid-vegetative growth, elevated CO2 significantly reduced leaf nitrogen concentrations by up to 44%," but they add that "plant nitrogen concentrations only differed by 8% among CO2 treatments at harvest while N2 fixation was increased," and they say that data from their experiment suggest that "symbiotic N2 fixation is important for maintaining seed N concentrations and that CO2 enhancement of symbiotic N2 fixation may compensate for low soil N availability."

Tu et al. state that a number of experiments, like theirs, "have shown that elevated CO2 can offset the adverse effects of O3 on crop biomass production and yield," citing the studies of Olszyk et al. (2000), Fuhrer (2003) and Fiscus et al. (2005). In addition, they note that "the protective effect of elevated CO2 against O3 injury has been observed in a number of C3 plant species, including cotton, peanut, rice, soybean, and wheat, due in large part to a reduction in O3 uptake from reduced stomatal conductance and possibly from increases in photoassimilation rates and antioxidant metabolism," citing the work of McKee et al. (2000), Booker and Fiscus (2005), Fiscus et al. (2005) and Booker et al. (2007).

Clearly, therefore, and contrary to the blatantly false contention of the United States Environmental Protection Agency, CO2 is not a pollutant; it is a pollution fighter that reduces the negative effects of true pollutants, such as ozone, and replaces them with positive effects that are of great worth to man and nature alike.

Additional References
Booker, F.L., Burkey, K.O., Pursley, W.A. and Heagle, A.S. 2007. Elevated carbon dioxide and ozone effects on peanut: I. Gas-exchange, biomass, and leaf chemistry. Crop Science 47: 1475-1487.

Booker, F.L. and Fiscus, E.L. 2005. The role of ozone flux and antioxidants in the suppression of ozone injury by elevated CO2 in soybean. Journal of Experimental Botany 56: 2139-2151.

Fiscus, E.L., Booker, F.L. and Burkey, K.O. 2005. Crop responses to ozone: Uptake, modes of action, carbon assimilation and partitioning. Plant, Cell and Environment 28: 997-1011.

Fuhrer, J. 2003. Agroecosystem responses to combinations of elevated CO2, ozone, and global climate change. Agriculture, Ecosystems and Environment 97: 1-20.

McKee, I.F., Mulholland, B.J., Craigon, J., Black, C.R. and Long, S.P. 2000. Elevated concentrations of atmospheric CO2 protect against and compensate for O3 damage to photosynthetic tissues of field-grown wheat. New Phytologist 146: 427-435.

Olszyk, D.M., Tingey, D.T., Watrud, L., Seidler, R. and Andersen, C. 2000. Interactive effects of O3 and CO2: Implications for terrestrial ecosystems. In Singh (Ed.) Trace Gas Emissions and Plants. Kluwer Academic, Dordrecht, the Netherlands, pp. 97-136.

Archived 29 September 2010