PHOTOSYNTHETIC AND STOMATAL RESPONSES OF AVENA-SATIVA (POACEAE) TO A VARIABLE LIGHT ENVIRONMENT

The net photosynthetic (A), stomatal conductance to water vapor (g), water use efficiency (WUE = A/transpiration), and leaf water potential (psi) responses of cultivated oats (Avena sativa)were determined under an experimental regime of alternating full sun (photosynthetic photon flux density, PPFD > 1,700 mumol . m2 . sec-1) and shade (300-400 mumol . m-2 . sec-1 PPFD). Less extensive measurements were made on winter wheat (Triticum aestivum) to test the generality of crop species' responses. The rates of stomatal opening/closing after changes in PPFD in A vena and Triticum were compared with previously determined rates for native grasses and forbs to assess how domestication might have altered stomatal dynamics. Characteristics of Avena under alternating sun and shade were 1) rapid fluctuations in A between full sun (approximately 27 mumol . m-2 . sec-1) and shade rates (approximately 12-13 mumol . m-2 . sec-1); 2) slower changes in g, causing progressive stomatal closure during the measurement sequence and possible stomatal limitation of A; 3) no change in leaf psi; and 4) a net reduction in WUE. Triticum had similar sun/shade A, g, and WUE dynamics, except that Triticum stomata returned to full-sun g between shade periods. The rates of change of g in Avena and Triticum were lower than for some desert and subalpine native species, but were similar to rates for species in adjoining native habitat. The basic stomatal dynamics of A vena and Triticum may typify many cultivated C3 species, and these data indicate that crop stomatal behavior has not diverged significantly from that of native species.