© 2001 Heron Publishing—Victoria, Canada
Responses of foliar δ13C, gas exchange and leaf morphology to reduced hydraulic conductivity in Pinus monticola branches
Lucas A. Cernusak (1, 2) and John D. Marshall (1)
1. Department of Forest Resources, University of Idaho, Moscow, ID 83844-1133, USA / 2. Environmental Biology Group and CRC for Greenhouse Accounting, Research School of Biological Sciences, Australian National
University, GPO Box 475, Canberra, ACT 2601, Australia / Received December 5, 2000
Summary
We tested the hypothesis that branch hydraulic conductivity partly controls foliar stable carbon isotope ratio (δ13C) by its influence on stomatal conductance in Pinus monticola Dougl. Notching and phloem-girdling treatments were applied to reduce branch conductivity over the course of a growing season.
Notching and phloem girdling reduced leaf-specific conductivity (LSC) by about 30 and 90%, respectively. The 90% reduction
in LSC increased foliar δ13C by about 1‰ (P < 0.0001, n = 65), whereas the 30% reduction in LSC had no effect on foliar δ13C (P = 0.90, n = 65). Variation in the δ13C of dark respiration was similar to that of whole-tissues when compared among treatments. These isotopic measurements, in
addition to instantaneous gas exchange measurements, suggested only minor adjustments in the ratio of intercellular to atmospheric
CO2 partial pressures (ci/ca) in response to experimentally reduced hydraulic conductivity. A strong correlation was observed between stomatal conductance
(gs) and photosynthetic demand over a tenfold range in gs. Although ci/ca and δ13C appeared to be relatively homeostatic, current-year leaf area varied linearly as a function of branch hydraulic conductivity
(r2 = 0.69, P < 0.0001, n = 18). These results suggest that, for Pinus monticola, adjustment of leaf area is a more important response to reduced branch conductivity than adjustment of ci/ca.
Keywords:
carbon isotope ratio, intercellular CO2 concentration, leaf area.
