CO2alters water use, carbon gain, and yield for the dominant species in a natural grassland.
Global atmospheric CO2is increasing at a rate of 1.5-2 ppm per year and is predicted to double by the end of the next century. Understanding how terrestrial ecosystems will respond in this changing environment is an important goal of current research. Here we present results from a field study of elevated CO2in a California annual grassland. Elevated CO2led to lower leaf-level stomatal conductance and transpiration (approximately 50%) and higher mid-day leaf water potentials (30-35%) in the most abundant species of the grassland, Avena barbata Brot. Higher CO2concentrations also resulted in greater midday photosynthetic rates (70% on average). The effects of CO2on stomatal conductance and leaf water potential decreased towards the end of the growing season, when Avena began to show signs of senescence. Water-use efficiency was approximately doubled in elevated CO2, as estimated by instantaneous gas-exchange measurements and seasonal carbon isotope discrimination. Increases in CO2and photosynthesis resulted in more seeds per plant (30%) and taller and heavier plants (27% and 41%, respectively). Elevated CO2also reduced seed N concentrations (9%).
Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA.
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Jackson
Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA.|Department of Ecology, Faculty of Agronomy, University of Buenos Aires, Av San Martín 4453, Buenos Aires, Argentina.
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Sala
Carnegie Institution of Washington, 290 Panama Street, 94305, Stanford, CA, USA.
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Field
Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA.
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Mooney
Annual grassland; Avena barbata CO2; Reproduction; Water relations