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Links between Transpiration and Plant Nitrogen: Variation with Atmospheric CO2 Concentration and Nitrogen Availability

H. Wayne Polley, Hyrum B. Johnson, Charles R. Tischler and H. Allen Torbert
International Journal of Plant Sciences
Vol. 160, No. 3 (May 1999), pp. 535-542
DOI: 10.1086/314145
Stable URL: http://www.jstor.org/stable/10.1086/314145
Page Count: 8
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Links between Transpiration and Plant Nitrogen: Variation
with Atmospheric CO2 Concentration and
Nitrogen Availability
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Abstract

Transpiration is closely linked to plant nitrogen (N) content, indicating that global or other changes that alter plant N accumulation or the relative requirements of plants for water and N will affect transpiration. We studied effects of N availability and atmospheric CO2 concentration, two components of global biogeochemistry that are changing, on relationships between whole‐plant transpiration and N in two perennial C3 species, Pseudoroegneria spicata (a tussock grass) and Gutierrezia microcephala (a half‐shrub). Two indices of plant N requirement were used: N accretion (N in live and dead tissues) and N loss in litter (N in dead tissues). Transpiration was analyzed as the product of N accretion or loss by plants and the ratio of transpiration to N accretion or loss. The two indices of plant N requirement led to different conclusions as to the effects of N availability on plant use of water relative to N. Transpiration scaled proportionally with N accretion, but transpiration per unit of N loss declined at high N. Carbon dioxide enrichment had little effect on the ratio of transpiration to N accretion and no effect on transpiration per unit of N loss. The two species accumulated similar amounts of N, but the half‐shrub used more than twice as much water as the grass. Nitrogen availability and CO2 concentration influenced whole‐plant transpiration more by changing plant N accumulation than by altering the stoichiometry between transpiration and plant N. Species differences in total water use, by contrast, reflected differences in the scaling of transpiration to plant N. A better understanding of species differences in water and N dynamics may thus be required to predict transpiration reliably.

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