, Volume 151, Issue 3, pp 372-386
Date: 15 Nov 2006

Variation in leaf physiology of Salix arctica within and across ecosystems in the High Arctic: test of a dual isotope (Δ13C and Δ18O) conceptual model

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Leaf carbon isotope discrimination (Δ13C) varies with the balance between net photosynthesis (A) and stomatal conductance (g s ). Inferences that can be made with Δ13C are limited, as changes could reflect variation in A and/or g s . Investigators have suggested that leaf δ18O enrichment above source water (Δ18O) may enable differentiation between sources of variation in Δ13C, as leaf Δ18O varies with transpiration rate (E), which is closely correlated with g s when leaves experience similar leaf to air vapor pressure differences. We examined leaf gas exchange of Salix arctica at eight sites with similar air temperatures and relative humidities but divergent soil temperatures and soil water contents near Pituffik, Greenland (76°N, 38°W). We found negative correlations at the site level between g s and Δ18O in bulk leaf tissue (r 2 = 0.62, slope = −17.9‰/mol H2O m−2 s−1, = 0.02) and leaf α-cellulose (r 2 = 0.83, slope = −11.5‰ mol H2O m−2 s−1, P < 0.01), consistent with the notion that leaf water enrichment declines with increasing E. We also found negative correlations at the site-level between intrinsic water-use efficiency (iWUE) and Δ13C in bulk leaf tissue (r 2 = 0.65, slope = −0.08‰/μmol CO2 /mol H2O, = 0.02) and leaf α-cellulose (r 2 = 0.50, slope = −0.05 ‰/[μmol CO2 /mol H2O], = 0.05). When increasing Δ13C was driven by increasing g s alone, we found negative slopes between Δ13C and Δ18O for bulk leaf tissue (−0.664) and leaf α-cellulose (−1.135). When both g s and A max increased, we found steeper negative slopes between Δ13C and Δ18O for bulk leaf tissue (−2.307) and leaf α-cellulose (−1.296). Our results suggest that the dual isotope approach is capable of revealing the qualitative contributions of g s and A max to Δ13C at the site level. In our study, bulk leaf tissue was a better medium than leaf α-cellulose for application of the dual isotope approach.

Communicated by Dan Yakir.