Effects of plant size and water relations on gas exchange and growth of the desert shrub <i>Larrea tridentata</i>

TitleEffects of plant size and water relations on gas exchange and growth of the desert shrub Larrea tridentata
Publication TypeJournal Article
Year of Publication1994
AuthorsFranco A.C., de Soyza A.G., Virginia R.A, Reynolds J.F., Whitford WG
Date Published1994
Call Number00456
Keywordsarticle, articles, gas-exchange,Larrea, journal, journals, Larrea,gas-exchange, Larrea,phenology, Larrea,water relations, phenology,Larrea, stomatal conductance,Larrea, water relations,Larrea

Larrea tridentata is a xerophytic evergreen shrub, dominant in the arid regions of the southwestern United States. We examined relationships between gas-exchange characteristics, plant and soil water relations, and growth responses of large versus small shrubs of L. tridentata over the course of a summer growing season in the Chihuahuan Desert of southern New Mexico, USA. The soil wetting front did not reach 0.6 m, and soils at depth of 0.6 and 0.9 m remained dry throughout the summer, suggesting that L. tridentata extracts water largely from soil near the surface. Surface soil layers (<0.3 m) were drier under large plants, but pre-dawn xylem water potentials were similar for both plant sizes suggesting some access to deeper soil moisture reserves by large plants. Stem elongation rates were about 40% less in large, reproductively active shrubs than in small, repoductively inactive shrubs. Maximal net photosynthetic rates (Pmax) occurred in early summer (21.3 u mol m-2 s -1), when pre-dawn xylem water potential (XWP) reached ca. -1MPa. Although both shrub sizes exhibited similar responses to environmental factors, small shrubs recovered faster from short-term drought, when pre-dawn XWP reached about -4.5 MPa and Pmax decreased to only ca. 20% of unstressed levels. Gas exchange measurements yielded a strong relationship between stomatal conductance and photosynthesis, and the relationship between leaf-to-air vapor pressure deficit and stomatal conductance was found to be influenced by pre-dawn XWP. Our results indicate that stomatal repsonses to water stress and vapor pressure deficit are important in dtermining rates of carbon gain and water loss in L. tridentata.