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Effects of leaf area index and species distribution on ecosystem CO2 and water fluxes.
SPARKS, JED1, HARLEY, PETER2, TURNIPSEED, ANDREW1, SPARKS, KIMBERLEE1, HUXMAN, TRAVIS1, MONSON, RUSSELL1, 1 2
ABSTRACT- During the summers of 1999 and 2000 we compared fluxes from the eastern and western fetch directions at the Niwot Ridge AMERIFLUX eddy correlation tower to determine if differences in leaf-area index (LAI), species composition, and forest density alter ecosystem carbon fixation, water vapor efflux, and ecosystem water-use efficiency (WUE). The eastern fetch is dominated by Pinus contorta, exhibits a LAI of 3.74 m2 m-2, and a tree density of 0.45 trees m-2. The western fetch is a mixture of Pinus contorta, Picea engelmannii, and Abies lasiocarpa, exhibits a LAI of 4.33 m2 m-2, and a tree density of 0.35 trees m-2. Average net carbon uptake was higher from the western (5.38 ± 0.08 mol CO2 m-2) compared to the eastern fetch (4.42 ± 0.11 mol CO2 m-2). Additionally, water vapor fluxes were 18-20% higher in the western compared to the eastern fetch. Despite differences in LAI, species composition, and tree density, ecosystem-level WUE was similar in both forests (1.72 ± 0.15 and 1.65 ± 0.09 mmol mol-1 in the eastern and western forest, respectively). Instantaneous leaf-level measurements of WUE were 5.55 ± 0.76, 4.56 ± 0.35, and 4.30 ± 0.49 mmol mol-1 in P. contorta, P. engelmanii, and A. lasiocarpa, respectively. It appears differences in species-level WUE, LAI, and tree density are not manifested annually at the ecosystem level due to differential patterns of soil evaporation.
KEY WORDS: water-use efficiency, carbon sequestration, eddy flux, alpine