title: Antecedent moisture and seasonal precipitation influence the response of canopy-scale carbon and water exchange to rainfall pulses in a semi-arid grassland.
abstract: The influences of prior monsoon-season drought (PMSD) and the seasonal timing of episodic rainfall ('pulses') on carbon and water exchange in water-limited ecosystems are poorly quantified. *In the present study, we estimated net ecosystem exchange of CO(2) (NEE) and evapotranspiration (ET) before, and for 15 d following, experimental irrigation in a semi-arid grassland during June and August 2003. Rainout shelters near Tucson, Arizona, USA, were positioned on contrasting soils (clay and sand) and planted with native (Heteropogon contortus) or non-native invasive (Eragrostis lehmanniana) C4 bunchgrasses. Plots received increased ('wet') or decreased ('dry') monsoon-season (July-September) rainfall during 2002 and 2003. Following a June 2003 39-mm pulse, species treatments had similar NEE and ET dynamics including 15-d integrated NEE (NEE(pulse)). Contrary to predictions, PMSD increased net C uptake during June in plots of both species. Greater flux rates after an August 2003 39-mm pulse reflected biotic activity associated with the North American Monsoon. Furthermore, August NEE(pulse) and ecosystem pulse-use efficiency (PUE(e) = NEE(pulse)/ET(pulse)) was greatest in Heteropogon plots. PMSD and rainfall seasonal timing may interact with bunchgrass invasions to alter NEE and ET dynamics with consequences for PUE(e) in water-limited ecosystems.
authors: University of Arizona, Department of Ecology and Evolutionary Biology, Tucson, AZ, USA. dpotts@uci.edu
authors: D L
authors: DL
authors: Potts
authors: T E
authors: TE
authors: Huxman
authors: J M
authors: JM
authors: Cable
authors: N B
authors: NB
authors: English
authors: D D
authors: DD
authors: Ignace
authors: J A
authors: JA
authors: Eilts
authors: M J
authors: MJ
authors: Mason
authors: J F
authors: JF
authors: Weltzin
authors: D G
authors: DG
authors: Williams