Global Change Biology (2004) 10, 1810–1819, doi: 10.1111/j.1365-2486.2004.00840.x 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? L. H. ZISKA*,C.F.MORRISw and E . W. G O I N S * *Alternate Crop and Systems Laboratory, USDA Agricultural Research Service, Beltsville, MD 20705, USA, wWestern Wheat Quality Laboratory, USDA Agricultural Research Service, Pullman, Washington, DC 99164, USA Abstract The sensitivity of yield and quality parameters to carbon dioxide concentration [CO2] was determined for individual lines of hard-red spring wheat released in 1903, 1921, 1965 and 1996. All cultivars were evaluated with respect to growth and vegetative characteristics, grain yield and nutritional quality in response to [CO2] increases that corresponded roughly to the CO2 concentrations at the beginning of the 20th century, the current [CO2], and the future projected [CO2] for the end of the 21st century, respectively. Leaf area ratio (cm2 gÀ1) declined and net assimilation rate (g m2 dayÀ1) increased in response to increasing [CO2] for all cultivars during early vegetative growth. By maturity, vegetative growth of all cultivars significantly increased with the increase in [CO2]. Seed yield increased significantly as [CO2] increased, with yield sensitivity to rising [CO2] inversely proportional to the year of cultivar release. Greater [CO2] yield sensitivity in older cultivars was associated with whole-plant characteristics such as increased tillering and panicle formation. Grain and flour protein, however, declined significantly with increasing [CO2] and with year of release for all cultivars, although absolute values were higher for the older cultivars. Overall, these data indicate that yield response at the whole-plant level to recent and projected increases in [CO2] has declined with the release of newer cultivars, as has protein content of grain and flour. However, if agronomic practice can be adapted to maximize individual plant performance, [CO2] responsive characteristics of older cultivars could, potentially, be incorporated as factors in future wheat selection. Keywords: breeding, carbon dioxide, Chris, grain quality, Marquis, Oxen, protein, seed yield, Thatcher, wheat Received 6 June 2003; revised version received 26 January 2004 and accepted 23 February 2004 century (Intergovernmental Panel on Climate Change Introduction scenario’s IS 92e and IS 92a, respectively, in Schimel Data from the carbon dioxide information analysis et al., 1996). Because rising atmospheric CO2 represents center indicate a 30% increase in the global back- a resource for plant growth, exploitation of this ground concentration of atmospheric carbon dioxide resource to optimize yield for agronomic productivity À1 [CO2], from 290 to 375 mmol mol during the last 100 has been suggested with future CO2 increases, and years, with the largest increase in recent decades (i.e. significant intraspecific variation in yield response with À1 310–375 mmol mol since 1955, Keeling & Whorf, 2001). a doubling of current CO2 levels has been observed in It is anticipated that the global background [CO2] will cowpea (Ahmed et al., 1993), rice (Ziska et al., 1996; continue to increase with concentrations projected to Moya et al., 1998), and soybean (Ziska et al., 1998). approach 500–700 mmol molÀ1 by the end of the current The importance of wheat as a global staple for human and animal nutrition is indisputable (e.g. Evans, 1998). Correspondence: L. H. Ziska, tel. 1 1 301 504 6639, Wheat has been grown in the North American prairie fax 1 1-301-504-5824, e-mail: [email protected] for over a 100 years and breeding efforts regarding 1810 r 2004 Blackwell Publishing Ltd EVALUATION OF WHEAT VARIETIES TO INCREASING CO2 1811 diseases, pest resistance, early maturity, and enhanced end of the 20th century as well as that projected for the grain and baking quality during this time have been end of the 21st century. Actual [CO2] values (Æ SD) continuous (Bonjean & Angus, 2001). The growth and averaged throughout the experiment were 293 Æ 19, yield response of modern wheat lines has been 385 Æ 15 and 715 Æ 14 mmol molÀ1. Two to three seeds evaluated with respect to recent 20th century [CO2] of each cultivar were sown in 0.6 L pots filled with increases (Polley et al., 1993), and both old and modern vermiculite and thinned to one seedling 4–6 days after Spring wheat lines have been evaluated for projected, emergence for each [CO2], 35–40 plants of a given future atmospheric [CO2] (Mandersheid & Weigel, cultivar were used. All pots were watered to the drip 1997; Kimball et al., 2001). However, wheat lines point daily with a complete nutrient solution contain- released throughout the 20th century have not been ing 14.5 mmol mÀ3 nitrogen (Robinson, 1984). All seed evaluated regarding the increase in atmospheric [CO2] was provided by Dr Ravindra Dezkota of South Dakota that occurred during this period (ca. 30%). Yet, a State University. quantitative and qualitative assessment of reproductive For each chamber, temperature was varied in a sensitivity to rising [CO2] for lines released at the diurnal fashion from an overnight low of 20 1Ctoa beginning and end of the 20th century would be crucial maximum afternoon value of 30 1C, with an average in determining potential changes in yield and quality daily (24 h) value of 23.1 1C. Average daily tempera- for both old and modern wheat lines, as well as in tures for South Dakota (where Spring wheat is grown identifying those plant characteristics that contribute to exclusively) range from 20 1C in late June during [CO2] responsiveness. heading, to 24 1C during maturation in July and To initiate such an assessment, we evaluated four August, although monthly values as low as 17.5 and different lines of spring wheat introduced over the as high as 26.5 1C have been recorded (http:// last 93 years, to recent (i.e. 290–375 mmol molÀ1) and www.lwf.ncdc.noaa.gov). Light (photosynthetically ac- future increases (i.e. 375–720 mmol molÀ1) in atmo- tive radiation, PAR) was also altered diurnally in spheric carbon dioxide at the single plant level. While conjunction with temperature with the highest PAR assessment on a plant basis does not reflect field values, value (1000 mmol m2 sÀ1) occurring during the after- such an approach has distinct validity since increasing noon. Daily PAR was 13 h, supplied by a mixture of yields are related, in large part, to selection for whole- high-pressure sodium and metal halide lamps and 2 À1 plant characteristics such as harvest index or average averaged 24.5 mol m day for all chambers. The CO2 kernel weight (e.g. Evans, 1998; Bonjean & Angus, concentration of the air was controlled by adding either 2001). In the current study, lines were evaluated with CO2 or CO2-free air to maintain the desired CO2 respect to the [CO2] responsiveness of these growth concentration. CO2-free air was obtained using a CO2 characteristics, as well as vegetative parameters and scrubber (Ballston 75–60 type, Ballston Filter products, seed yield. In addition, because increasing [CO2] can Lexington, MA, USA). Injection of CO2 and CO2-free air significantly alter protein concentration relative to was controlled by a TC-2 controller using input from an carbohydrate (e.g. Blumenthal et al., 1996; Rogers absolute infrared gas analyzer (WMA-2, PP Systems, et al., 1998; Kimball et al., 2001), wheat and flour quality Haverhill, MA, USA). Temperature, humidity and was determined separately as a function of cultivar and [CO2] were recorded every 15 min and averages rising [CO2]. recorded on a daily basis for all experimental runs. Additional details concerning the operating system can be found in Ziska et al. (2001). Materials and methods Cultivars were harvested at four different growth Because no system has yet been devised to expose stages during development; tiller initiation, flag leaf plants to subambient [CO2] under field conditions for development, panicle emergence and maturity. These 24 h dayÀ1 (see Mayeux et al., 1993) these experiments correspond approximately to 2.0, 8, 10.1 and 11.4 on the were conducted in controlled environment chambers. Feekes small grains scale, respectively. Although the Seed from four cultivars of hard-red spring wheat more recently introduced cultivars, Chris and Oxen (Triticum aestivum L.) introduced during the 20th matured earlier, [CO2] did not affect the time to century, Marquis (1903), Thatcher (1921), Chris (1965) maturity for any cultivar. To minimize root binding, and Oxen (1996) were grown using three controlled all cultivars were transplanted to 4.5 L pots following environmental chambers (EGC Corp., Chagrin Falls, tiller initiation. Plants from a given cultivar were OH, USA) with each chamber maintained at one grouped together, but groups were spaced so as to of three CO2 concentration set-points, 290, 370 and minimize mutual shading. Both individual plants and 720 mmol molÀ1 for 24 h dayÀ1. These concentrations groups were rotated weekly inside the chambers until approximated the [CO2] present at the beginning and heading to minimize border effects. r 2004 Blackwell Publishing Ltd, Global Change Biology, 10, 1810–1819 1812 L. H. ZISKA et al. At each harvest, eight plants per cultivar and [CO2] product. Flour ash was determined by Method 08-01 treatment were sampled. Leaf area was determined (AACC, 2000) (low values are desired). Milling score is photometrically on all leaves for the first three growth a composite number that encompasses straight flour stages, and estimated from the relationship between yield, break flour yield and ash (high values desired). A leaf weight and area (r2 of 0.89) from leaf samples for all mixograph analysis reflects mixing time requirement cultivar–treatment combinations at plant maturity.