Interactive Effects of Elevated CO2 and Temperature on Crops

Concerns about the enrichment of atmospheric CO2 and its association with global warming that will likely have potential impacts on crop production, have drawn attention of plant scientists to study the combined effects of elevated CO2 and high temperature on plants, especially crops (Idso et al. 1987; Rawson 1992; Morison and Lawlor 1999). As mentioned earlier, crops respond positively to elevated CO2 and negatively to high temperature, but what about the interactive effects of these two environmental factors? Previous studies have shown that elevated CO2 can partially ameliorate some of the adverse effects of environmental stresses, including high temperature (Qaderi et al. 2006), salinity (Bray and Reid 2002) and ultraviolet-B radiation (Qaderi and Reid 2005) on crops. Even though elevated CO2 can mitigate the detrimental effects of the above-optimal temperatures on crop growth and yield, certainly temperatures near the upper limit for crops will negatively affect yields, regardless of CO2 concentration (Polley 2002).

Crop responses to elevated CO2 are strongly related to temperature (Wheeler et al. 1994). Both of these environmental factors affect crop yields, in terms of seed quantity and quality. In a meta-analysis of FACE experiments, Ainsworth and Long (2005) have shown that the herbaceous crop yield increased on average by 17% and the above-ground dry matter production for trees increased 28%. In contrast, Lobell et al. (2006) developed statistical crop models, using outputs from multiple climate models and considering six California perennial food crops, and predicted that temperature-induced decreases in yields of these crops will likely occur by 2050. Also, Prasad et al. (2005) have reported that elevated CO2 can increase yields of grain legume crops (e.g., soybean, dry bean (Phaseolus vulgaris L.) peanut, and cowpea [Vigna unguiculata (L.) Walp.)], but this beneficial effect is offset by negative effects of the above-optimum temperature, which leads to decreased seed yield and quality. Thomas et al. (2003) have shown that, in soybean grown under five temperature regimes and two CO2 concentrations, carbon dioxide had no effect on seed composition and transcript, whereas temperature had a pronounced effect on mature seed composition (e.g., total oil, ratio of fatty acids, nitrogen, phosphorus, carbohydrate) and transcript (e.g., p-glucosidase) in developing seeds (Table 1.1).

Vu et al. (1997) have found that elevated CO2 enhanced leaf photosynthetic CO2 assimilation rates, but CO2 enrichment and high temperature reduced Rubisco content in rice and soybean. Variation in the responses of these two crop species to these two environmental factors suggests an interspecific variation among C3 plants in response to future global climate change. Ziska et al. (1996) studied the response of 17 rice cultivars to increased CO2 and temperature and reported that at elevated CO2, plant growth and yield were higher under lower temperature than under higher temperature regime and there was variation among rice cultivars.

Alterations in the air temperature and its interaction with elevated CO2 can affect photosynthesis. Based on the biochemical models of photosynthesis (Farquhar et al. 1980), other models that simulate this interaction have been

Table 1.1 Responses of some crop species to the stimulatory effects of elevated CO2 at high





Strong response

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