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Photosynthesis, Transpiration, and Ribulose Bisphosphate Carboxylase of Selected Crested Wheatgrass Plants¹

Information on rates of physiological processes is needed to identify genotypes differing in physiological characteristics for use in varietal improvement programs. Apparent photosynthesis (AP), transpiration (E), stomatal conductance (r_c), ribulose bisphosphate Carboxylase (RuBPc), specific leaf weight (SLW), and stoma frequency were measured in diploid, tetraploid, and hexaploid crested wheatgrass [Agropyron cristatum (L.) Gaertn.] plants from Iran to determine rates for these physiological processes in this species. Two named varieties of crested wheatgrass, A. desertorum (Fisch. ex Link) Schult. ‘Nordan’ and A. cristatum ‘Ruff’ were also evaluated.

Mean AP rates were 22.0, 12.5, and 12.2 mg CO₂ dm^-3 hour^-1 and mean E rates were 2.7, 1.4, and 1.6 g H₂O dm^-2 hour-¹ for greenhouse-grown tetraploid, hexaploid, and diploid plants, respectively. Field-grown (natural water stress) hexaploid plants had higher AP rates (18.1 and 10.4 mg CO₂ dm^-2 hour^-1 in 1976 and 1977, respectively) than did tetraploid plants (13.1 and 8.3). Activity of RuBPc averaged 12.1, 6.9, and 11.0 µnoles CO²/(mg protein)^-1 hour^-1 for greenhouse-grown hexaploids, tetraploids, and diploid plants, respectively, and 8.7, 7.6, and 7.4 for field-grown plants. The field soil was a Parshall fine sandy loam (Pachic haploborolls). The fact that tetraploid plants had the higher AP rates and dry matter production under non-water stress growing conditions in the greenhouse may indicate a greater potential for increased growth and yield as compared with the other plants evaluated in this study. Hexaploids had the higher SLW with the tetraploids and diploids having similar and lower SLW. Stomate frequency was greater for the tetraploids as compared with hexaploid plants.

In the greenhouse, the tetraplotd plants fixed more CO₂ per unit of RuBPc than either the diploid or hexaploid plants. Both greenhouse and field hexaploid plants had high RuBPc activity, but with less range in AP rates than greenhouse (nonstressed) and field (stressed) tetraploid plants which indicated that either stomatal response is sluggish in the hexaploids or that these plants are capable of fixing greater amounts of CO₂ under waterstress conditions. The latter quality may indicate greater drought tolerance.

Key Words: Stomatal resistance • Stomatal conductance • Ribulose bisphosphate Carboxylase • Transpiration • Stomata • Grasses • Forage grass • Agropyrom cristatum (L.) Gaertn

² Plant physiologist, AR, SEA, USDA, Northern Great Plains Res. Ctr., Box 459, Mandan, ND 58554.

Received for publication May 13, 1979.