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Elevated CO2 Increases Photosynthesis and Water-Use Efficiency in Peas
Gavito, M.E., Curtis, P.S., Mikkelsen, T.N. and Jakobsen, I.  2000.  Atmospheric CO2 and mycorrhiza effects on biomass allocation and nutrient uptake of nodulated pea (Pisum sativum L.) plants. Journal of Experimental Botany 52: 1931-1938.

What was done
Peas (Pisum sativum L.) were grown in growth chambers for 60 days at atmospheric CO2 concentrations of 350 and 700 ppm.  In addition, half of the peas in each CO2 treatment were inoculated with mycorrhizal fungi, while the other half were not inoculated.  Thus, the authors studied the interactive effects of elevated CO2 and mycorrhizal inoculation in this agricultural species.

What was learned
There were no significant interactive effects between elevated CO2 and mycorrhizal inoculation for any measured parameters.  Nonetheless, as a main effect, elevated CO2 increased photosynthetic rates by 53%.  In addition, when photosynthetic capacity was measured at various atmospheric CO2 concentrations, no signs of photosynthetic acclimation were detected.

The CO2-induced increases in photosynthesis contributed to total dry weight increases of 15 and 19% for non-inoculated and inoculated plants, respectively.  Although total water use was unchanged by atmospheric CO2 enrichment, plants grown at 700 ppm CO2 exhibited a water-use efficiency that was 27% greater than that displayed by plants grown at the ambient CO2 concentration.

What it means
As the atmospheric CO2 concentration rises, it is likely that pea plants will exhibit increased rates of photosynthesis and biomass production, regardless of their association with mycorrhizal fungi.  In addition, when exposed to greater atmospheric CO2 concentrations, such pants will also likely increase their water-use efficiency, possibly providing farmers with significant savings in the form of unused irrigation water allotments that could be redirected elsewhere.