TITLE:
Comparative Gas Exchange of Ulmus crassifolia (Cedar Elm, Ulmaceae) and Ungnadia speciosa (Mexican Buckey, Sapindaceae) at Ambient and Elevated Levels of Light, CO2 and Temperature
AUTHORS:
Matthew B. Grunstra, Oscar W. Van Auken
KEYWORDS:
Light Response, Gas Exchange, Photosynthesis, Respiration, Water Use Efficiency
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.14 No.6,
June
30,
2023
ABSTRACT: Ulmus
crassifolia Nutt. (Cedar elm, Ulmaceae) is a tree found in central and east Texas, northern
Mexico, east to Florida, and north to southern Missouri and Oklahoma. Ungnadia speciosa Endl. (Mexican-buckeye,
Sapindaceae) is a shrub or small tree found in woodlands and savannas of
central and western Texas, southern New
Mexico and northern Mexico. In central Texas, both species are found in Juniperus ashei/Quercus
virginiana woodlands or savannas or also at low density in
inter-canopy grassland gaps or patches. Environmental conditions in this area
are stressful because of shallow soils, high summer temperatures, and
inconsistent low rainfall. Currently, both species have a low density in these areas, and Ulmus crassifolia is
usually a tree, while Ungnadia
speciosa is a woody understory shrub. This study suggests U. crassifolia
and U. speciosa are tolerant or intermediate species, with juveniles starting
in shade. Maximum photosynthetic rate (Amax),
dark respiration (Rd), intercellular CO2, light
saturation (Lsp) and water
use efficiency significantly increased when light levels and CO2 concentrations were elevated for both species, but not when temperatures were
elevated. Stomatal conductance decreased when the CO2 concentration
doubled, but there were few effects from
elevated temperature. These findings suggest that U. speciosa and U. crassifolia should be more common and imply that they will have a higher density in a
future high CO2 environment.