Submitted to: Global Change Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/10/2004
Publication Date: 10/1/2004
Citation: Ziska, L.H., Morris, C.F., Goins, E.W. 2004. Quantitative and qualitative evaluation of selected wheat varieties released since 1903 to increasing atmospheric carbon dioxide: can yield sensitivity to carbon dioxide be a factor in wheat performance. Global Change Biology. 10(10):1810-1819. Interpretive Summary: In addition to being the principle greenhouse gas, carbon dioxide (CO2) is also the principle source of carbon for photosynthesis and plant growth. As such, crops may grow more as CO2 increases. However, are the crop varieties that exist today the most carbon dioxide responsive lines? To answer this question for wheat (the world's most abundant crop), we examined four different Spring wheat varieties introduced in 1903, 1921, 1965 and 1996. Between 1903 and 1996, the concentration of carbon dioxide in the atmosphere increased from approximately 295 parts per million (ppm) to 370 ppm. However, the newer varieties did not show a stronger carbon dioxide response when growth and yield were compared at a common CO2 concentration of 290 and 370 ppm. Rather, the older varieties showed a greater sensitivity to carbon dioxide. Furthermore, these same varieties showed a stronger response to projected carbon dioxide increases (720 ppm) during the 21st century. In addition, the newer varieties showed a strong decrease in protein content and baking quality relative to the older varieties as carbon dioxide increased. Overall, these data indicate that crop breeders have not been selecting for the most CO2 responsive wheat varieties. The data argue for an active CO2 selection program that could be used to maximize wheat yields in response to global carbon dioxide increases.
Technical Abstract: The sensitivity of yield and quality parameters to carbon dioxide concentration [CO2] was determined for four lines of hard-red spring wheat released in 1903, 1921, 1965, and 1996. Environmental growth chambers were used to simulate past, current, and future atmospheric [CO2]. All cultivars were evaluated with respect to growth and vegetative characteristics, grain yield, and nutritional quality in response to [CO2]. Leaf area ratio (LAR) declined and net assimilation rate (NAR) increased in response to recent and future [CO2] increases for all cultivars during early vegetative growth. Vegetative growth was significantly greater with increasing [CO2]. Seed yield increased significantly with [CO2], with yield sensitivity inversely proportional to year of release. This resulted mainly from reduced tiller formation and subsequent panicle production in newer cultivars. Grain and flour protein declined significantly with increasing [CO2] and with year of release. Overall, these data indicate that yield response to increasing [CO2] has declined with the release of newer cultivars, as has protein content. It suggests that at least at the whole plant level, empirical selection for yield during the 20th century has not chosen, de facto, the most [CO2] sensitive wheat cultivars.