© 1994 Heron Publishing—Victoria, Canada
Variation in foliar δ13C values within the crowns of Pinus radiata trees
Richard H. Waring (1) and Warwick B. Silvester (2)
1. College of Forestry, Oregon State University, Corvallis, Oregon 97331, USA / 2. / Department of Biological Sciences, The University of Waikato, Private Bag 3105, Hamilton, New Zealand / Received February 16, 1994
Summary
Although herbaceous species generally show little within plant variation in δ13C, trees show large spatial and temporal differences. We found that the aspect of exposure and branch length accounted for
up to 6‰ δ13C difference within the foliage of individual trees of Pinus radiata D. Don. The foliage on branches 0.5 m in length was as much as 4‰ more depleted in 13C than foliage on 10-m long branches, and an additional 2‰ more depleted on the shaded side than on the exposed side. We confirmed
that on clear days, relative branch hydraulic conductivity, defined as the ratio of transpiration to the water potential gradient,
was much higher in short branches than in long branches. Stomatal conductance remained high in foliage on short branches during
the day, whereas it declined progressively in long-branch foliage under similar conditions. These differences were sufficient
to explain the observed variation in δ13C in foliage on long and short branches.
Keywords:
carbon isotopes, hydraulic conductance, isotope fractionation, stomatal conductance, water potential.
