April 20, 2012

For Wheat and Rice, CO2 is Nice

Filed under: Adaptation, Plants

We have written about the biological benefits of elevated temperatures and atmospheric CO2 levels hundreds of times, and we will never run out of new material! Evidence the results of two recent article showing how CO2 improves the yield of wheat and the competitiveness of rice.

A team of seven scientists from various agencies in China began their article noting “In the past 100 years, the mean surface temperature in China has increased by 0.4–0.6ºC, and it is expected that the average surface temperature in western China will rise by 1.7ºC in the next 30 years and by 2.2ºC over the next 50 years.” Furthermore, Xiao et al. report “The annual mean rainfall decreased by about 60 mm [~2.4 in.] from the 1950s to the 1990s in semiarid regions of China, and a loss of soil moisture through evaporation increased 35–45 mm [~1.5 in.] due to the temperature increase. The rainfall and available soil moisture throughout the entire growing stage of the crops was about 100 mm [~4 in.] lower in the 1990s than in the 1950s. As a result, concerns about the vulnerability of agricultural production to climate change are increasing. For example, it is likely that evaporation will increase and soil moisture will decline in many regions as the temperature increases.” If that is not enough bad news, they state “There is now strong evidence that overall crop yields will decrease by 5–10% in China by 2030 as a result of climatic changes, and that the yields of wheat, rice and maize will be greatly reduced.”

But, then, quite importantly, they add “The impact of future climate change on crop production has been widely predicted by modeling the interaction between crops and climate change; however, few observations of the impacts of climate change on crop production have been reported.” [emphasis added]

Xiao and colleagues from the Institute of Arid Meteorology of the China Meteorological Administration set out to help remedy this deficiency.

And were they ever in for a surprise.

Xiao et al. grew wheat in China at several different relatively high elevation sites (1,798 m at Tongwei and 2,351 m at LuLu Mountain), and the artificially increased the temperature up to 2.2ºC. At the Tonwei site, the elevated temperatures increased grain output by over 3% and by up to 6% at LuLu Mountain. Not surprisingly, they write “These findings indicate that an increase in temperature will improve the winter wheat yield at two different altitudes.”

That finding certainly runs counter to the pre-existing model-based expectations!

And that’s not all. Xiao and team note “The results of this study revealed that a 0.6–2.2°C increase in temperature improved the water use efficiency (WUE) of winter wheat plants at both elevations evaluated.” More good news!

And when they consider the effect of CO2, things get even better.

They summarize their thoughts on CO2 with “Model projections have suggested that, although increased temperature and decreased soil moisture will reduce global crop yields by 2050, the direct fertilization effect of rising CO2 will offset these losses.”

And, echoing something that we must have said a thousand times, Xiao et al. go on to conclude “In general, a higher atmospheric CO2 concentration increases plant production as a result of higher rates of photosynthesis and increased water use efficiency.”

In the end, Xiao et al. have this to say “It is expected that by 2030 warming temperatures and changes in rainfall will have led to the increase of 3.1% in wheat yields at a low altitudes and of 4.0% in wheat yields at high altitude in semiarid northwestern China, and that by 2050, there will have been the additional increase of 2.6% and 6.0%, respectively, at these altitudes”. Further, “In addition, the results of this study revealed that a 0.6–2.2ºC increase in temperature will improve the water use efficiency of winter wheat plants at both altitudes evaluated here.”

So while they went into their experiment expecting bad news for winter wheat, they come out of it extoling the virtues of CO2 and a warmer climate on winter wheat yields.

Add the Xiao et al. study to the huge amount of research showing that crops, forests, and/or grasslands will benefit from the effects of elevated atmospheric CO2 concentrations with or without changes to temperature. Our critics just cannot accept the good news and insist that something will surely spoil the benefits.

For example, one thing we hear over and over is that weeds will out-compete more desirable plants and create an ecological disaster sometime down the road (after we pass another tipping-point?).

A recent article hits this issue head-on, and our critics will not be happy. A team of scientists from China and Norway supported financially by the National Natural Science Foundation of China and the Chinese Academy of Sciences grew rice and a weed (barnyard grass) in a paddy in eastern China at ambient (374 ppm) and ambient plus 200 ppm concentrations of atmospheric CO2. Zeng et al. conducted this experiment “in order to evaluate the impact of rising atmospheric carbon dioxide on nutrient competition between rice crop and weed. Results showed that elevated CO2 significantly enhanced the biomass, tillers, leaf area index and net assimilation rate of rice, but reduced those of barnyard grass after elongation.” They report “As a result, significant increase of the ratios of rice/barnyard grass of biomass and absolute nutrient uptake were observed under elevated CO2. The results suggest that rising atmospheric CO2 concentration could alter the competition between rice and barnyard grass in paddy fields in favor of rice.”

You come to World Climate Report to get the facts, and as these two studies continue to show, the evidence is overwhelming that the biosphere will be enhanced in the future, despite the claims to the contrary espoused by the more alarmist types out there.

Be sure to keep coming back for more!


Xiao, G. Q. Zhang, Y. Li, R. Wang, Y. Yao, H. Zhao, and H. Bai. 2010. Impact of temperature increase on the yield of winter wheat at low and high altitudes in semiarid northwestern China. Agricultural Water Management, 97, 1360–1364.

Zeng, Q., B. Liu, B. Gilna, Y. Zhang, C. Zhu, H. Ma, J. Pang, G. Chen, and J. Zhu. 2011. Elevated CO2 effects on nutrient competition between a C3 crop (Oryza sativa L.) and a C4 weed (Echinochloa crusgalli L.). Nutrient Cycling in Agroecosystems, 89, 93–104.

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