Forest harvest can have significant impacts on forest ecosystems that may
influence the capacity of soils to sequester carbon (C). The microbial community
controls decomposition, which is a critical process in partitioning litter- and root-C
between CO₂ and storage in semi-permanent soil-C pools. The objectives of this study
were to determine the effect of clear-cutting and stand age on: 1) temporal dynamics
of soil microbial community (SMC) structure and physiological status; and 2) shifts
among microbial functional groups in taking up ¹³C-labeled plant materials during
decomposition. The experiment was conducted in Douglas-fir ecosystems within the
Gifford Pinchot National Forest, Washington. We chose stands of three different
ages: old-growth where trees are between 300 and 500 years old; an 8-year old stand;
and a 25-year old stand. Phospholipid fatty acid (PLFA) profiling and ¹³C-PLFA
labeling techniques along with the ratio of saturated to monounsaturated PLFAs and
the ratios of cyclopropyl PLFAs to their monoenoic precursors as microbial
physiological stress markers were utilized.
Microbial PLFA profiles showed that SMC structure and physiological status
was most affected by season and secondarily by time since clear-cutting. Total
microbial biomass and bacterial and fungal biomass were significantly reduced in CC8
but not in CC25 sites relative to old-growth sites. Total microbial biomass
concentration was lowest and the stress indicators were highest in August, which
corresponded to low soil moisture and high temperatures.
The relative amount of ¹³C incorporated into PLFAs was also influenced by
stand age and ¹³C source (¹³C-labeled litter vs. ¹³C-labeled root material). A
significantly greater amount of ¹³C was incorporated in CC8 samples compared to
OG1 samples in five out of the seven sample dates. Additionally, a significantly
greater proportion of ¹³C was incorporated into soil samples containing the ¹³C-labeled
litter material relative to samples containing ¹³C-labeled root material in four out of
the seven dates. In general, 18:lω9 and 18:2ω6,9 (common fungal biomarkers) had
the greatest amount of ¹³C incorporation throughout the study period in both clear-cut
and old-growth sites, indicating the important role of fungi in the decomposition of
litter and root material and translocation of C within soil layers. / Graduation date: 2006
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28797 |
| Date | 01 June 2005 |
| Creators | Kucera, Jennifer Moore |
| Contributors | Dick, Richard P. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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