title: Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO2 and H2O in a sotol grassland in Big Bend National Park, Texas.
abstract: Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is anticipated to affect biosphere/atmosphere exchanges of both CO(2) and H(2)O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level fluxes of CO(2) and H(2)O 1 day before and up to 7 days after three supplemental precipitation pulses in the summer (June, July, and August 2004). In addition, the responses of leaf, soil, and ecosystem fluxes of CO(2) and H(2)O to these precipitation pulses were also evaluated in September, 1 month after the final seasonal supplemental watering event. We found that plant carbon fixation responded positively to supplemental precipitation throughout the summer. Both shrubs and grasses in watered plots had increased rates of photosynthesis following pulses in June and July. In September, only grasses in watered plots had higher rates of photosynthesis than plants in the control plots. Soil respiration decreased in supplementally watered plots at the end of the summer. Due to these increased rates of photosynthesis in grasses and decreased rates of daytime soil respiration, watered ecosystems were a sink for carbon in September, assimilating on average 31 mmol CO(2) m(-2) s(-1) ground area day(-1). As a result of a 25% increase in summer precipitation, watered plots fixed eightfold more CO(2) during a 24-h period than control plots. In June and July, there were greater rates of transpiration for both grasses and shrubs in the watered plots. In September, similar rates of transpiration and soil water evaporation led to no observed treatment differences in ecosystem evapotranspiration, even though grasses transpired significantly more than shrubs. In summary, greater amounts of summer precipitation may lead to short-term increased carbon uptake by this sotol grassland ecosystem.
authors.affiliation: Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409-3131, USA. lisa.patrick@ttu.edu
authors.forename: Lisa
authors.initials: L
authors.lastname: Patrick
authors.forename: Jessica
authors.initials: J
authors.lastname: Cable
authors.forename: Daniel
authors.initials: D
authors.lastname: Potts
authors.forename: Danielle
authors.initials: D
authors.lastname: Ignace
authors.forename: Greg
authors.initials: G
authors.lastname: Barron-Gafford
authors.forename: Alden
authors.initials: A
authors.lastname: Griffith
authors.forename: Holly
authors.initials: H
authors.lastname: Alpert
authors.forename: Natasja
authors.initials: N
authors.lastname: Van Gestel
authors.forename: Traesha
authors.initials: T
authors.lastname: Robertson
authors.forename: Travis E
authors.initials: TE
authors.lastname: Huxman
authors.forename: John
authors.initials: J
authors.lastname: Zak
authors.forename: Michael E
authors.initials: ME
authors.lastname: Loik
authors.forename: David
authors.initials: D
authors.lastname: Tissue
mesh_terms: D000070357:Asparagaceae / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D017753:Ecosystem; D018515:Plant Leaves / Q000378:metabolism*; D006109:Poaceae / Q000378:metabolism; D011891:Rain; D012621:Seasons; D012987:Soil / Q000032:analysis*; D013781:Texas; D014867:Water / Q000378:metabolism*
chemical_list: D012987:Soil; D014867:Water; D002245:Carbon Dioxide