Pa. Fay et Ak. Knapp, PHOTOSYNTHETIC AND STOMATAL RESPONSES TO VARIABLE LIGHT IN A COOL-SEASON AND A WARM-SEASON PRAIRIE FORB, International journal of plant sciences, 157(3), 1996, pp. 303-308
Species differences in photosynthetic and stomatal responses to steady
-state and variable light were examined in two cooccurring tallgrass p
rairie forbs, the cool-season legume Baptisia bracteata var. glabresce
ns and the warm-season composite Helianthus annuus. Previous studies i
ndicated that these species might have similar responses to short-term
, minutes-long shade because of their similar growth forms. However, p
hotosynthetic carbon gain, oxygen evolution, transpiration, and leaf x
ylem pressure potential measurements showed that Helianthus was far mo
re responsive than Baptisia to changes in light availability. Helianth
us had higher photosynthetic capacity, photosynthetic temperature opti
mum, stomatal conductance, and transpiration rates, rapid stomatal clo
sure during shade, and delayed photosynthetic recovery when light leve
ls increased, traits common to species exposed to high temperatures or
periodic drought stress. Baptisia, active under cooler, wetter condit
ions than Helianthus, had lower photosynthetic capacity, photosyntheti
c temperature optimum, stomatal conductance, and transpiration, and no
stomatal response to shade, responses typifying species that experien
ce little water stress. We suggest that environmental and physiologica
l factors may combine to reinforce greatly different photosynthetic an
d stomatal responses to short-term shade in species with similar growt
h form, especially in habitats with long, seasonally varying growing c
onditions.