CARBON ISOTOPE DISCRIMINATION AND WATER-USE EFFICIENCY IN 4 COOL-SEASON GRASSES

Carbon isotope discrimination (DELTA) has been correlated with water use efficiency (WUE) in several C3 plant species and may be useful as a plant selection factor for improving WUE in crops. Research was undertaken to determine if differences in DELTA could be found in grass accessions from the National Plant Germplasm System and if DELTA of field grown plant tissue could be linked to WUE in greenhouse pots (pot WUE). Leaf DELTA was measured on several accessions of Agropyron desertorum (Fischer ex Link) Schultes (standard crested wheatgrass), Festuca arundinacea Schreb. (tall fescue), Dactylis glomerata L. (orchardgrass), and Lolium perenne L. (perennial ryegrass). Accessions were established and grown under irrigated and dryland conditions at Central Ferry, WA and dryland conditions at Pullman, WA in the spring and summer of 1988. Differences in DELTA among accessions within species were significant, but the environment by accession (within species) interaction was not, indicating that accession differences in DELTA were generally consistent across environments. Measurements of pot WUE (dry weight/pot evapotranspiration) were made under greenhouse conditions on accessions of Dactylis, Festuca, and Lolium that had high and low field DELTA and dry matter productivity. Accessions selected for low field DELTA always had higher pot WUE based on shoot dry weight than high DELTA selections under well-watered and drought-stressed conditions. This was also true of pot WUE based on whole-plant dry weight in all cases except Festuca under drought-stress. Accessions with low field DELTA had higher water potential, solute potential, and turgor pressure than high DELTA accessions in the greenhouse experiment, suggesting a more favorable water status for growth. The results link pot WUE with field DELTA in a way consistent with theoretical expectations and suggest that DELTA can be effectively used to evaluate C3 grass germplasm for WUE.