PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Proceedings-Research on Coniferous Forest Ecosystems-A symposium .
Bellingham, Washington-March 23-24, 197 2
Initial steps in decomposition
of Douglasfir needles
under forest conditions
Abstract
P. L . Minyar d
Graduate Student i n
Forest Pathology
Douglas-fir (Pseudotsuga menziesii) needle decomposition was evaluated after 6 and 12 months exposure t o
forest floor conditions by characterizing solubility changes of saccharides, waxes and oils, and cellulose. Th e
results lead to the hypothesis that primary processes of decomposition are initiated on the outside of the needl e
with the solubilization of waxes and, as the waxes are depleted, the cellular constituents are solubilized.
and
C . H . Drive r
Professor of
Forest Pathology
College of Forest Resources
University of Washingto n
Seattle, Washingto n
Introduction
Approximately 4 percent of the biomass of
the Douglas-fir consists of needles (Dic e
1970) containing a portion of the carbon to
be cycled within the ecosystem . Some genera
of the Moniliales have been reported that are
capable of utilizing cellulose and breakin g
down needle waxes to release carbo n
(Macauley and Thrower 1966 ; Martin and
Juniper 1970) . The decomposition of needl e
litter and the release of carbon in a forest is
important in the nutrient cycling processe s
within a conifer ecosystem . In an effort to
study carbon cycling pathways and the par t
played by the processes of the decompositio n
of Douglas-fir needles the following investigation
was conducted .
Primary decomposition is defined a s
changes in solubility of the needle constituents.
Therefore to study decompositio n
techniques were used to detect changes i n
solubility . Simplistically, needles consist of an
outer layer of cutin and waxes and an inne r
cellular layer made up of cellulose and protoplasmic
contents. Needle constituents wer e
divided into three classes : (1) compound s
extractable with hexane (primarily cuticl e
waxes) (Martin and Juniper 1970), (2) those
extractable with hot water (saccharides)
(Campbell 1952), and (3) cellular components
soluble in 1 percent HaOH (hemicellulose )
(Campbell 1952) .
Materials and Methods
Needles used in this study were collected i n
the following manner . Screen traps wer e
attached to a tower at random intervals i n
height from just below the crown of the tree s
to ground level . Needles were collected fro m
the traps aseptically, placed in sterile containers,
and transported to the laboratory for
analysis and further study. In addition needle s
from the traps were placed in nylon mes h
bags on the forest floor and allowed to de -
compose. After exposure for 6 and 12 months
the needle samples were analyzed in th e
following manner .
Samples were oven dried for 24 hr . at
105°C and stored in airtight containers unti l
analyzed .
Three 8-g replications of each treatmen t
sample of needles were extracted with boiling
n-hexane in a Soxhlet extractor for 6 hr . and
oven dried for 24 hr. at 105°C to remove the
hexane and weighed . The amount of material
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