© 1996 Heron Publishing—Victoria, Canada
Carbon partitioning in Pinus radiata stands in relation to foliage nitrogen status
Peter N. Beets (1) and David Whitehead (2)
1. New Zealand Forest Research Institute, Private Bag RO 3020, Rotorua, New Zealand / 2. New Zealand Forest Research Institute, PO Box 69, Lincoln 8152, New Zealand / Received April 10, 1995
Summary
First rotation Pinus radiata D. Don trees were grown on a nitrogen-deficient sand dune in an experimental design that included lupin (Lupinus arboreus Sims) as an understory species, and biennial application of balanced fertilizer in a replicated split-plot factorial design
with thinning treatments as subplots. From an initial 2222 stems ha–1, stands were thinned to 1483 and 741 trees ha–1 at ages 2 and 4 years, respectively. Mean annual production of foliage, branches, stem, coarse roots, and cones was estimated
from measurements of the dry matter content at ages 7, 10, 11 and 17 years. A model was used to estimate total above- and
belowground dry matter production from measurements of leaf area index and foliar nitrogen concentration. An estimate of fine
root production was obtained from the difference between the model estimate of total production and the estimate of aboveground
production.
The fertilizer and lupin treatments increased foliage nitrogen concentration, leaf area index and dry matter production of
most aboveground components. In unthinned stands, foliage production ranged from 3 to 6 Mg ha–1 year–1, branch production from 1 to 4 Mg ha–1 year–1, and stem production from 8 to 19 Mg ha–1 year–1, depending on site fertility. Partitioning of aboveground production to foliage, branches, stems, and cones changed with
tree age but it was not significantly influenced by the treatments. The fractions of aboveground dry matter production partitioned
to foliage, branches, stems and cones were 0.23, 0.12, 0.63 and 0.02, respectively, for trees between ages 7 and 11 years,
and 0.21, 0.08, 0.67 and 0.04, respectively, for trees between ages 11 and 17 years. With increasing foliage nitrogen concentration,
partitioning to branches increased significantly, whereas partitioning to stems decreased.
The fraction of total dry matter production partitioned to stems decreased significantly with thinning from 0.40 to 0.27 with
a concomitant increase in the fraction partitioned to fine roots from 0.31 to 0.46. The average fraction partitioned to fine
roots was 0.46 and 0.30 in unfertilized and fertilized stands, respectively. Stem production was more highly correlated with
fine root partitioning than with leaf area index. Fine root production was not significantly affected by fertilizer application.
The ratio of total net primary production to leaf area index increased significantly with thinning, but not with site fertility
or stand age. The ratio of aboveground dry matter production to leaf area index increased with stand age and with the application
of fertilizer but not with thinning.
Keywords:
forest growth, nitrogen fertilization, plantation forest.
