Temperature and precipitation controls over leaf- and ecosystem-level CO 2 flux along a woody plant encroachment gradient

Greg A. Barron-Gafford, Russell L. Scott, G. Darrel Jenerette, Erik P. Hamerlynck, Travis E. Huxman

Research output: Contribution to journalArticle

46 Scopus citations

Abstract

Conversion of grasslands to woodlands may alter the sensitivity of CO 2 exchange of individual plants and entire ecosystems to air temperature and precipitation. We combined leaf-level gas exchange and ecosystem-level eddy covariance measurements to quantify the effects of plant temperature sensitivity and ecosystem temperature responses within a grassland and mesquite woodland across seasonal precipitation periods. In so doing, we were able to estimate the role of moisture availability on ecosystem temperature sensitivity under large-scale vegetative shifts. Optimum temperatures (T opt) for net photosynthetic assimilation (A) and net ecosystem productivity (NEP) were estimated from a function fitted to A and NEP plotted against air temperature. The convexities of these temperature responses were quantified by the range of temperatures over which a leaf or an ecosystem assimilated 50% of maximum NEP (Ω 50). Under dry pre- and postmonsoon conditions, leaf-level Ω 50 in C 3 shrubs were two-to-three times that of C 4 grasses, but under moist monsoon conditions, leaf-level Ω 50 was similar between growth forms. At the ecosystems-scale, grassland NEP was more sensitive to precipitation, as evidenced by a 104% increase in maximum NEP at monsoon onset, compared to a 57% increase in the woodland. Also, woodland NEP was greater across all temperatures experienced by both ecosystems in all seasons. By maintaining physiological function across a wider temperature range during water-limited periods, woody plants assimilated larger amounts of carbon. This higher carbon-assimilation capacity may have significant implications for ecosystem responses to projected climate change scenarios of higher temperatures and more variable precipitation, particularly as semiarid regions experience conversions from C 4 grasses to C 3 shrubs. As regional carbon models, CLM 4.0, are now able to incorporate functional type and photosynthetic pathway differences, this work highlights the need for a better integration of the interactive effects of growth form/functional type and photosynthetic pathway on water resource acquisition and temperature sensitivity.

Original languageEnglish (US)
Pages (from-to)1389-1400
Number of pages12
JournalGlobal change biology
Volume18
Issue number4
DOIs
StatePublished - Apr 1 2012

Keywords

  • Eddy covariance
  • Mesquite (Prosopis velutina)
  • Net ecosystem exchange
  • Photosynthesis
  • Respiration
  • Temperature optima
  • Vegetative change
  • Woody plant encroachment

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Ecology
  • Environmental Science(all)

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