Carbon isotope discrimination and yield in 14 cool-season grasses

Selection for carbon isotope discrimination (delta) has potential for improving water-use efficiency in cool-season grasses. An understanding of how delta is affected by differential water application and its association with dry mater yield may be helpful in identifying the best cool-season grass species for breeding and improvement, and may assist in designing selection and breeding procedures for improving cool-season grasses. We designed a study to evaluate the response of delta and dry matter yield to a gradient of water application in 14 cool-season, perennial grasses. The grasses were established in a rainout shelter facility equipped with a line-source irrigation system to study the: i) trends in dry matter yield across 6 water levels (WL-1 through 6, ranging from 981 to 64 mm water applied) and delta across 3 water levels (WL-1, 3, and 5), ii) grass x water level interactions for these traits, and iii) relationship between dry matter yield and delta in these grasses across a 2-year period. When averaged across years, the grasses differed significantly for delta at the highest (WL-1) and lowest (WL-5) water levels, but not at WL-3. Reductions in delta were strongly linear from WL-1 to WL-5, and although some inconsistencies were evident, the trend was similar for all grasses. Grasses differed significantly for dry matter yield at each of the water levels. Although the change in dry matter yield was mostly linear across water levels, the trend was not consistent among the grasses. In general, delta was not closely associated with dry matter yield; however, some exceptions with high dry matter yield and high delta were evident. This lack of close association between dry matter yield and delta in these 14 grasses suggests that breeding efforts to improve these grasses should involve simultaneous selection for dry matter yield and delta. DOI:10.2458/azu_jrm_v56i6_johnson