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Growth, nitrogen uptake, and metabolism in two semiarid shrubs grown at ambient and elevated atmospheric CO₂ concentrations: effects of nitrogen supply and source¹

²Department of Biology, Duke University, Durham, North Carolina, 27708 USA; ³Department of Crop Science, P.O. Box 7620, North Carolina State University, Raleigh, North Carolina 27695 USA; ⁴Department of Biology and Division of Environmental Science and Policy, Nicholas School of the Environment & Earth Science, Phytotron Building, Box 90340, Duke University, Durham, North Carolina 27708-0340 USA

The effect of differences in nitrogen (N) availability and source on growth and nitrogen metabolism at different atmospheric CO₂ concentrations in Prosopis glandulosa and Prosopis flexuosa (native to semiarid regions of North and South America, respectively) was examined. Total biomass, allocation, N uptake, and metabolites (e.g., free NO₃^–, soluble proteins, organic acids) were measured in seedlings grown in controlled environment chambers for 48 d at ambient (350 ppm) and elevated (650 ppm) CO₂ and fertilized with high (8.0 mmol/L) or low (0.8 mmol/L) N (N_level), supplied at either 1 : 1 or 3 : 1 NO₃^– : NH₄⁺ ratios (N_source). Responses to elevated CO₂ depended on both N_level and N_source, with the largest effects evident at high N_level. A high NO₃^– : NH₄⁺ ratio stimulated growth responses to elevated CO₂ in both species when N was limiting and increased the responses of P. flexuosa at high N_level. Significant differences in N uptake and metabolites were found between species. Seedlings of both species are highly responsive to N availability and will benefit from increases in CO₂, provided that a high proportion of NO₃- to NH₄-N is present in the soil solution. This enhancement, in combination with responses that increase N acquisition and increases in water use efficiency typically found at elevated CO₂, may indicate that these semiarid species will be better able to cope with both nutrient and water deficits as CO₂ levels rise.

Key Words: ammonium • CO₂ • controlled environments • nitrate • nitrogen metabolism • nitrogen uptake • Prosopis flexuosa • Prosopis glandulosa

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				H. F. Causin, T. W. Rufty, and J. F. Reynolds Gas exchange and carbon metabolism in two Prosopis species (Fabaceae) from semiarid habitats: effects of elevated CO2, N supply, and N source Am. J. Botany, May 1, 2006; 93(5): 716 - 723. [Abstract] [Full Text] [PDF]