Nitrogen availability and mycorrhizal colonization influence water use efficiency and carbon isotope patterns in Pinus sylvestris

• Published in: The New phytologist 2004-12, Vol.164 (3), p.515-525
• Main Authors: Hobbie, Erik A., Colpaert, Jan V.
• Format: Article
• Language: English
• Subjects: bioavailability; Biological and medical sciences; carbon; Carbon dioxide; Carbon isotopes; compound‐specific; ecosystem respiration; ectomycorrhizae; exponential growth; Fundamental and applied biological sciences. Psychology; isotopes; Leaves; mathematical models; microbial colonization; Mycorrhizal fungi; Nitrogen; Parasitism and symbiosis; Perlite; Photosynthesis; Pinus sylvestris; Plant nutrition; Plant physiology and development; Plants; Scots pine (Pinus sylvestris); Suillus; Suillus luteus; Symbiosis; Thelephora; Thelephora terrestris; Water use efficiency
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2004.01187.x

• 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. • We 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. • We 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.