1. Nitrogen availability and mycorrhizal colonization influence water use efficiency and carbon isotope patterns in Pinus sylvestris
- Author
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Erik A. Hobbie and Jan V. Colpaert
- Subjects
Physiology ,chemistry.chemical_element ,Plant Science ,Biology ,Photosynthesis ,biology.organism_classification ,Nitrogen ,chemistry ,Agronomy ,Isotopes of carbon ,Botany ,Ecosystem respiration ,Mycorrhiza ,Water-use efficiency ,Carbon ,Transpiration - Abstract
Summary • Nitrogen availability and colonization by mycorrhizal fungi may influence plant budgets of water, carbon, and carbon isotopes ( δ 13 C), but estimates of water use efficiency (WUE) derived from isotopic vs budgetary measurements are rarely compared. •W e assessed patterns of WUE, C allocation, and δ 13 C in cultures of nonmycorrhizal and ectomycorrhizal Pinus sylvestris at two N supply rates, 3% d − 1 and 5% d − 1 . • Mycorrhizal colonization increased δ 13 C at low N but not at high N. Relative to foliage, roots and mycorrhizal fungi were enriched in 13 C 1.5‰ and 3‰, respectively. 13 C fractionation during synthesis of transfer compounds of − 1.5‰ could account for this progressive enrichment. Increasing N availability increased instantaneous WUE by 7% but decreased budget-based WUE by 20%. WUE calculated isotopically was 10 times higher than budget-based WUE. Plants in our system therefore transpired most water without concurrent photosynthesis. •W e conclude that WUE depends on N concentration and not on the rate of N supply. The proportion of transpiration uncoupled from photosynthesis may largely control WUE in well-watered ecosystems, and this proportion depends on N concentration in the soil solution. Carbon isotopes only correlate with WUE above a critical concentration of available N. Thus, quantitatively interpreting δ 13 C patterns requires knowledge about coupling among C, N, and water in the plant‐mycorrhizal‐soil system.
- Published
- 2004