Won’t Beat Your Wheat
Balling Jr., Ph.D.
current issue of New Phytologist
is completely devoted to the effect of elevated atmospheric carbon
dioxide on the global ecosystem. Not surprisingly, several of those
articles deal exclusively with wheat growth rates; indeed, wheat is very
popular with the scientific set, thanks to its responsiveness to weather
the first study, a team of scientists from the Netherlands, Argentina,
Denmark, and Germany built a sophisticated computer model of
wheat-growth processes. They tested that model using wheat grown at CO2
levels of 410 parts per million (ppm) and 680 ppm. Among their many
findings, Rodriguez and colleagues reported that "elevated CO2 promoted final biomass by 12 percent" and
"photosynthesis was increased by 33 percent" when CO2 was higher. Radiation use efficiency, they found, increased
by 39 percent when atmospheric carbon dioxide rose.
from Arizona, Germany, and Nebraska developed a numerical model of wheat
growth that they compared with their model simulations to wheat grown in
central Arizona with natural and elevated (550 ppm) atmospheric CO2
concentrations. Grossman-Clarke and colleagues noted from the outset
that many previous studies had shown "an average increase in growth
and yield of about 30 percent" when CO2
doubled. In discussing final grain biomass, they found that "This
translates in a CO2
effect of 12 [percent] and 15 percent for the measurements and the
simulations, respectively, under unlimited water supply and the higher
values of 25 [percent] and 34 percent under water limitation."
Furthermore, "The CO2
effect on grain mass is clearly higher under water limitation for both
the measured and simulated results." They found that root biomass
increased under elevated CO2,
which gave the plants a competitive advantage in terms of water uptake.
finally, a team of scientists from Washington and Arizona grew spring
wheat over four different growing seasons in central Arizona in field
plots with atmospheric CO2 concentrations maintained at
natural (near 350 ppm) and 550 ppm. The levels of irrigation and
nitrogen fertilizer varied. When the nitrogen levels were low, the grain
quality and bread-making quality were negatively impacted by lower CO2. But they concluded that "with ample nitrogen fertilizer,
the effects will be minor."
three articles show us that with elevated atmospheric CO2
concentrations, a) wheat biomass will increase, b) wheat increases its
overall growth efficiency, and c) with adequate fertilizer, future grain
quality need not suffer.
Grossman-Clarke, S., et al.,. 2001. Modelling a spring wheat
crop under elevated CO2 and drought. New Phytologist, 150,
Kimball, B.A., et al.,. 2001. Elevated CO2,
drought and soil nitrogen effects on wheat grain quality. New Phytologist, 150,
Rodriguez, D., et al., 2001. Modelling the
response of wheat canopy assimilation to atmospheric CO2 concentrations. New