title: The sensitivity of ecosystem carbon exchange to seasonal precipitation and woody plant encroachment.
abstract: Ongoing, widespread increases in woody plant abundance in historical grasslands and savannas (woody encroachment) likely will interact with future precipitation variability to influence seasonal patterns of carbon cycling in water-limited regions. To characterize the effects of woody encroachment on the sensitivity of ecosystem carbon exchange to seasonal rainfall in a semi-arid riparian setting we used flux-duration analysis to compare 2003-growing season NEE data from a riparian grassland and shrubland. Though less seasonally variable than the grassland, shrubland NEE was more responsive to monsoon rains than anticipated. During the 2004-growing season we measured leaf gas exchange and collected leaf tissue for delta(13)C and nitrogen content analysis periodically among three size classes of the dominant woody-plant, Prosopis velutina and the dominant understory species, Sporobolus wrightii, a C(4) bunchgrass, present at the shrubland. We observed size-class and plant functional type independent patterns of seasonal plant performance consistent with greater-than-anticipated sensitivity of NEE in the shrubland. This research highlights the complex interaction between growing-season precipitation, plant-available alluvial groundwater and woody plant abundance governing ecosystem carbon balance in this semi-arid watershed.
authors.affiliation: Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA. dpotts@uci.edu
authors.forename: D L
authors.initials: DL
authors.lastname: Potts
authors.forename: T E
authors.initials: TE
authors.lastname: Huxman
authors.forename: R L
authors.initials: RL
authors.lastname: Scott
authors.forename: D G
authors.initials: DG
authors.lastname: Williams
authors.forename: D C
authors.initials: DC
authors.lastname: Goodrich
mesh_terms: D000704:Analysis of Variance; D001130:Arizona; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D017753:Ecosystem; D009584:Nitrogen / Q000032:analysis; D018515:Plant Leaves / Q000378:metabolism; D006109:Poaceae / Q000737:chemistry / Q000254:growth & development; D029862:Prosopis / Q000737:chemistry / Q000254:growth & development*; D011891:Rain
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D009584:Nitrogen