Photosynthetic Characteristics of Crested Wheatgrass and Bluebunch Wheatgrass

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Abstract
Light and temperature dependencies for net photosynthesis and stomatal conductance were generally very similar between foliage on crested wheatgrass (Agropyron desertorum (Fisch. ex Link) Schult.) plants and that on bluebunch wheatgrass (A. spicatum (Pursh) Scribn. and Smith) plants. The similarity of these gas exchange characteristics between the 2 bunchgrass species was true for foliage on unclipped plants as well as on partially defoliated plants. However, light and temperture dependencies of senescing leaf blades that were exserted in late-spring were significantly different for unclipped plants of these 2 species. Photosynthetic rates and stomatal conductances of senescent late-season blades on bluebunch wheatgrass plants were greater than those on crested wheatgrass plants at light intensities greater than 0.8 mmol photons m-2 s-1 (photosynthetic photon flux density) and at all foliage temperatures between 13.degree. C and 41.degree. C. These greater photosynthetic rates and stomatal conductances do not mean that blue-bunch wheatgrass tillers gained substantially more carbon or lost substantially more water than crested wheatgrass tillers. If both the photosynthetic area compositon of tillers and the environmental conditions of the northern Utah [USA] study site were considered, carbon gain and water loss for individual bluebunch wheatgrass tillers would be very similar to those for indiviudal crested wheatgrass tillers despite the significantly different responses to light and temperature during mid-summer.