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Response of Oats to Elevated CO2 and Disease
Malmstrom, C.M. and Field, C.B.  1997.  Virus-induced differences in the response of oat plants to elevated carbon dioxide.  Plant, Cell and Environment 20: 178-188.

What was done
Individual oat plants were grown for two months in pots placed within phytocells having atmospheric CO2 concentrations of 350 and 700 ppm.  In addition, one-third of the plants were infected with the barley yellow dwarf virus (BYDV), which plagues more than 150 plant species, including all major cereal crops, to determine whether infection with this pathogen would alter the growth response of oats to elevated CO2.

What was learned
Elevated CO2 stimulated rates of net photosynthesis in all plants, regardless of pathogen infection, with the greatest percentage increase occurring in diseased individuals (48% vs. 34%).  Moreover, atmospheric CO2 enrichment decreased stomatal conductance by 50% in infected plants and 34% in healthy ones, thus reducing transpirational water losses.  These phenomena contributed to a CO2-induced doubling of the instantaneous water-use efficiency in healthy control plants, and a larger increase of 2.7-fold in diseased plants infected with the virus.

Although BYDV infection reduced overall plant biomass, the growth response to elevated CO2 was greatest in the diseased plants.  After 60 days of CO2 enrichment, for example, total plant biomass increased by 36% in infected plants, while it only increased by 12% in healthy plants.  In addition, while elevated CO2 had little effect on root growth in healthy plants, it increased root biomass in infected plants by up to 60%.

What it means
As the CO2 content of the air continues to rise higher and higher, it is likely that oats will exhibit significant increases in net photosynthesis and growth.  Additionally, it is conceivable that if infected by BYDV, CO2-induced increases in these parameters will be even greater.  Also, in a future world of higher CO2 concentration, oats should benefit by displaying decreased rates of stomatal conductance and transpiration, and greater water-use efficiency, which again should be magnified if infected by BYDV.  Thus, the many positive effects of elevated CO2 on oats will likely offset some, if not most, of the negative effects of this virus on plant growth.  Indeed, in their concluding remarks, the authors stated that CO2 enrichment "may reduce losses of infected plants to drought," and "may enable diseased plants to compete better with healthy neighbors."

Reviewed 15 August 1999