© 1996 Heron Publishing—Victoria, Canada
Hydraulic conductance, light interception and needle nutrient concentration in Scots pine stands and their relations with
net primary productivity
Maurizio Mencuccini (1, 2) and John Grace (3)
1. Istituto di Ecologia Forestale e Selvicoltura, Università degli studi di Firenze, Via S. Bonaventura 13, 50145 Firenze, Italy / 2. Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY 14853-1801, USA / 3. Institute of Ecology and Resource Management, University of Edinburgh, Darwin Building, Mayfield Road, EH9 3JU Edinburgh,
U.K. / Received June 8, 1995
Summary
Aboveground xylem hydraulic conductance was determined in Scots pine (Pinus sylvestris L.) trees and stands from 7 to about 60 years of age. At the stand scale, leaf area index and net primary productivity (NPP,
above- plus belowground) increased and reached a plateau at about 25–30 and 15–20 years, respectively; both parameters declined
in mature stands. Stand hydraulic conductance followed a similar trend to NPP, with a maximum at about 15–20 years and a pronounced
reduction in old stands. At the tree scale, annual biomass growth per unit of leaf area (growth efficiency) declined with
tree age, whereas aboveground sapwood volume per unit leaf area, which is linearly related to maintenance respiration costs,
steadily increased. Radiation interception per unit leaf area increased significantly with reduced leaf area index of mature
stands, despite increased foliage clumping in the canopies of mature trees. Needle nutrient concentration did not change in
the chronosequence. Tree hydraulic conductance per unit leaf area was strongly and positively correlated with growth efficiency.
We discuss our findings in the context of growth reductions in mature and old trees, and suggest that increased hydraulic
resistance and maintenance respiration costs may be the main causes of reduced carbon gain in mature and old trees.
Keywords:
hydraulic architecture, Pinus sylvestris, respiration costs, transpiration.
