CHARACTERIZATION OF LIGNOCELLULOSE DECOMPOSITION IN STREAM WOOD SAMPLES USING CARBON-14 AND NITROGEN-15 TECHNIQUES

The distribution and lignocellulolytic activity of the microbial community on a Douglas fir log (Pseudotsuga menziesii) was studied in a Pacific Northwest stream. Microbial colonization and lignocellulolytic activity was shown to be a surface phenomenon. Incubations of {('14)C}lignocelluloses and wood samples in a mineral salts medium showed no increase in ('14)CO(,2) evolution over incubations in distilled water. Inorganic and organic nitrogen stimulated lignocellulose decay, with the greatest effect observed from (NH(,4))(,2)SO(,4) addition. Subsequent incubations revealed that KNO(,3) was most favorable to decay. Decomposition of {('14)C}lignocelluloses was greatest when incubated in stream water collected from four different sources than in distilled water. Phosphate and nitrate additions alone and in combination to a stream water medium yielded increases in {('14)C}cellulose decay, whereas {('14)C}lignin decomposition responded only to both in combination. Decomposition of {('14)C}lignocelluloses was greatest when KNO(,3) was added in concentrations (GREATERTHEQ) 10 mg N(.)l('-1) to a mineral salts medium. Decomposition rates increased three- to seven-fold over a range of temperatures from 5 to 22(DEGREES)C. Accumulation of filtrate NH(,4)('+) N (2-4 mg N(.)l('-1)) was always observed in incubations with KNO(,3) addition, and was independent of NO(,3)('-) concentrations (GREATERTHEQ) 10 mg N(.)1('-1). An incubation was conducted of stream wood samples with {('14)C}lignocelluloses in a mineral salts medium with K('15)NO(,3) (50% ('15)N). The organic nitrogen in the lignocellulose/wood sample mixture increases two-fold over the first 6 days. {('14)C}lignocellulose decomposition rates were greatest during the first 6 days, then diminished over the remaining 12 days, as did the rate of overall respiration. Filtrate NH(,4)('+) N increased from background levels to a final value of 57 ug N per treatment. Filtrate NO(,3)('-) disappeared by day 6, and organic nitrogen showed a slight decline between 12 and 18 days. The majority of the ('15)N that was accounted for (53%) was in the particulate organic fraction. By 18 days, the ('15)N enrichments of the filtrate NH(,4)('+), the organic fraction, and the inorganic nitrogen associated with the organic fraction had all increased to 20% ('15)N. Nitrogen fixation and denitrification measurements indicated insignificant gain/or loss of nitrogen from the incubations by these processes.