, Volume 169, Issue 2, pp 373–383 | Cite as

Response of dominant grass and shrub species to water manipulation: an ecophysiological basis for shrub invasion in a Chihuahuan Desert Grassland

  • Heather L. ThroopEmail author
  • Lara G. Reichmann
  • Osvaldo E. Sala
  • Steven R. Archer
Physiological ecology - Original research


Increases in woody vegetation and declines in grasses in arid and semi-arid ecosystems have occurred globally since the 1800s, but the mechanisms driving this major land-cover change remain uncertain and controversial. Working in a shrub-encroached grassland in the northern Chihuahuan Desert where grasses and shrubs typically differ in leaf-level nitrogen allocation, photosynthetic pathway, and root distribution, we asked if differences in leaf-level ecophysiology could help explain shrub proliferation. We predicted that the relative performance of grasses and shrubs would vary with soil moisture due to the different morphological and physiological characteristics of the two life-forms. In a 2-year experiment with ambient, reduced, and enhanced precipitation during the monsoon season, respectively, the encroaching C3 shrub (honey mesquite Prosopis glandulosa) consistently and substantially outperformed the historically dominant C4 grass (black grama Bouteloua eriopoda) in terms of photosynthetic rates while also maintaining a more favorable leaf water status. These differences persisted across a wide range of soil moisture conditions, across which mesquite photosynthesis was decoupled from leaf water status and moisture in the upper 50 cm of the soil profile. Mesquite’s ability to maintain physiologically active leaves for a greater fraction of the growing season than black grama potentially amplifies and extends the importance of physiological differences. These physiological and phenological differences may help account for grass displacement by shrubs in drylands. Furthermore, the greater sensitivity of the grass to low soil moisture suggests that grasslands may be increasingly susceptible to shrub encroachment in the face of the predicted increases in drought intensity and frequency in the desert of the southwestern USA.


Drought Photosynthesis Precipitation manipulation Water potential Woody encroachment 



We thank D.B. Hewins, N. Pierce, E. Johnson, L. Ebbs, and G.A. Gil for field assistance and K. Havstad, D. Peters, and the personnel of the Jornada Experimental Range site for logistical support. SRA and OES thank M.J. Trlica for introducing them many years ago and consequently providing the opportunity of working together. This work was supported by NSF grants to Arizona State University (DEB 09-17668), the University of Arizona (DEB 05-31691), and the Jornada LTER (DEB 06-18210) program, and by USDA-NRI 2008-35320-18684 to New Mexico State University.


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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Heather L. Throop
    • 1
    Email author
  • Lara G. Reichmann
    • 2
  • Osvaldo E. Sala
    • 2
  • Steven R. Archer
    • 3
  1. 1.Department of BiologyNew Mexico State UniversityLas CrucesUSA
  2. 2.School of Life Sciences and School of SustainabilityArizona State UniversityTempeUSA
  3. 3.School of Natural Resources and the EnvironmentUniversity of ArizonaTucsonUSA

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