Photosynthetic adaptation to temperature in four species from the Colorado shortgrass steppe: a physiological model for coexistence

Abstract

Several aspects of photosynthetic adaptation to temperature were examined in four graminoid species from the Colorado shortgrass steppe. The experimental species were chosen to provide examples of a variety of in situ seasonal phenology patterns. The cool season grass, Agropyron smithii (C), exhibited higher photosynthesis rates when grown in a cool temperature regime (20/15°C), and compared to warm grown plants (35/15°C). The warm season species, Bouteloua gracilis (C) and Buchloe dactyloides (C), exhibited higher photosynthetic capacities when grown in the warmer temperature regime. The sedge, Carex eleocharis (C), which exhibits seasonal growth potential during the cool and warm portions of the growing season, exhibited a marked capacity for photosynthetic temperature acclimation. Differential effects of growth temperature on the intracellular conductance to CO appeared to have a greater regulatory role in these responses for the two C species, relative to stomatal conductance or photorespiration (O inhibition of photosynthesis). In the two C species decreases in the intracellular conductance in cool grown plants were correlated with the decreased photosynthetic capacity in normal air for B. gracilis, but not for B. dactyloides. Analysis of the Arrhenius relationship for CO saturated net photosynthesis at low leaf temperatures (4.5-17°C) indicated sharp breaks in the apparent energy of activation at 5.8-9.0°C in the warm season species B. gracilis and B. dactyloides. Leaves of A. smithii and C. eleocharis exhibited no significant low temperature limitations according to this analysis. The low temperature limitations in the warm season species were partially reflected in an inhibition of the quantum yield for CO uptake after 2 h at 5-6°C in the presence of high photon flux densities. Temperature dependent increases in the chlorophyll fluorescence yield at high temperatures revealed the lowest breakpoint values for A. smithii, and the highest values for B. gracilis. The differential patterns of temperature adaptation among the species further extend the proposal of Kemp and Williams (1980; Ecology 61:846-858) that seasonal temperature gradients in the shortgrass steppe have a regulatory role in maintaining offset patterns of resource utilization and decreasing interspecific competition.

C 4 photosynthesis, atmospheric CO 2 , and climate

“…Numerous studies from grasslands throughout the world, including the Great Plains, have con®rmed the C 3 /C 4 transition in grassland composition correlated with temperature along a geographic gradient (Table 2) or on an interseasonal basis (Ode et al 1980;Barnes et al 1983;Monson et al 1983;Boryslawski and Bentley 1985) as predicted by the quantum yield model. It is unlikely that the strong agreements between predictions of C 3 /C 4 monocot transition based on quantum yield modeling analysis and ®eld observations are fortuitous.…”

“…However, where grasslands exhibit two distinct growing seasons (winter±spring and summer), strong seasonal dierences exist for the dominance of one pathway versus the other. Primary productivity in the central and northern portions of the Great Plains of North America is dominated by C 3 grasses in the spring growing season, while C 4 grasses predominate during the summer growing season (Ode et al 1980;Barnes et al 1983;Monson et al 1983;Boryslawski and Bentley 1985;Paruelo and Lauenroth 1996;Tieszen et al 1997). A similar pattern occurs in the Sonoran Desert, where the winter±spring vegetation is exclusively C 3 , whereas C 4 grasses dominate in the summer monsoon season (Shreve and Wiggins 1964;Mulroy and Rundel 1977).…”

Examining plant physiological responses to climate change through an evolutionary lens

“…Photorespiration scavenges some of the lost carbon from this process, but net losses of carbon and energy still occur. Evaporative water loss increases with photorespiration rates because greater stomatal conductance is necessary to make up for carbon losses (Monson et al, 1983).…”

Wetting and drying cycles drive variations in the stable carbon isotope ratio of respired carbon dioxide in semi-arid grassland

“…C 3 grasses are more competitive during years with moist, mild springs and dry summers; on the other hand, in years with dry springs and wet summers, C 4 species are favored (Monson et al 1983). In 2000, a dry spring was associated with lower C 3 /C 4 live biomass ratios compared to 2001, when more moisture allowed for superior growth of C 3 species.…”