Download Plants constantly face a tradeoff between CO2 uptake and water loss

The Linkage Between Fourteen Acacia Species’ Native Habitat and their Water Use Efficiency
Boyang Pan
Mentor: Diane Pataki
When leaf stomates are open, CO2 is taken up for photosynthesis and water is lost through transpiration. The
amount of CO2 fixed in photosynthesis per unit water lost in transpiration is the plant Water Use Efficiency
(WUE). WUE varies among species and is an important determinant for selecting plants that grow efficiently
with minimal water inputs. We do not currently have a means of predicting WUE; however, it is generally
assumed that species originating in more arid ecosystems will use less water and will have greater WUE. To
test this hypothesis, we investigated the linkage between plant water use efficiency and native ecosystem in 14
common horticultural shrub and tree species within the genus Acacia. All species were grown in an irrigated
common garden environment at the Los Angeles County Arboretum and Botanic Garden. Plant water use
efficiency was determined through carbon isotope analysis of bulk leaves and leaf soluble sugars, and leaf
transpiration was measured using a handheld porometer. Contrary to our hypothesis, Acacia species
originating in more arid ecosystems used more water and had lower WUE than Acacia species originating in
more temperate ecosystems. The results of this study indicate that under well-watered conditions arid species
may use more water than temperate species. Given the growing importance of water conservation in southern
California, an improved understanding of water use in horticultural plants will provide critical information for
selecting water efficient plants and determining plant irrigation needs.