Affiliation:
1. Departments of Microbiology, Soil Science, 2 and Fisheries and Wildlife, 3 Oregon State University, Corvallis, Oregon 97331-3804
Abstract
Surface wood samples obtained from a Douglas fir log (
Pseudotsuga menziesii
) in a Pacific Northwest stream were incubated in vitro with [
14
C]lignocellulose in a defined mineral salts medium supplemented with 10 mg of N liter
−1
of
15
N-labeled NO
3
−
(50 atom%
15
N). Evolution of
14
CO
2
, distribution and isotopic dilution of
15
N, filtrate N concentrations, and the rates of denitrification, N
2
fixation, and respiration were measured at 6, 12, and 18 days of incubation. The organic N content of the lignocellulose-wood sample mixture had increased from 132 μg of N to a maximum of 231 μg of N per treatment after 6 days of incubation. Rates of [
14
C]lignocellulose decomposition were greatest during the first 6 days and then began to decline over the remaining 12 days. Total CO
2
evolution was also highest at day 6 and declined steadily over the remaining duration of the incubation. Filtrate NH
4
+
-N increased from background levels to a final value of 57 μg of N per treatment. Filtrate NO
3
−
N completely disappeared by day 6, and organic N showed a slight decline between days 12 and 18. The majority of the
15
N that could be recovered appeared in the particulate organic fraction by day 6 (41 μg of N), and the filtrate NH
4
+
N fraction contained 11 μg of
15
N by day 18. The
15
N enrichment values of the filtrate NH
4
+
and the inorganic N associated with the particulate fraction had increased to approximately 20 atom%
15
N by 18 days of incubation, whereas the particulate organic fraction reached its highest enrichment by day 6. Measurements of N
2
fixation and denitrification indicated an insignificant gain or loss of N from the experimental system by these processes. The data show that woody debris in stream ecosystems might function as a rapid and efficient sink for exogenous N, resulting in stimulation of wood decomposition and subsequent activation of other N cycling processes.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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