Microbial decomposition of wood in streams: distribution of microflora and factors affecting (14C) lignocellulose mineralization

The distribution and lignocellulolytic activity of the microbial community wasdetermined on a large log of Douglas fir (Pseudotsuga menziesit) in a PacificNorthwest stream. Scanning electron microscopy, plate counts, and degradationof [14C]lignocelluloses prepared from Douglas fir and incubated with samples ofwood taken from the surface and within the log revealed that most of the microbialcolonization and lignocellulose-degrading activity occurred on the surface. La-beled lignocellulose and surface wood samples were incubated in vitro withnutrient supplements to determine potential limiting factors of C4Cflignocellulosedegradation. Incubations carried out in a nitrogenless mineral salts and traceelements solution were no more favorable to degradation than those carried out indistilled water alone. Incubations supplemented with either (NH4)2SO4 or organicnitrogen sources showed large increases in the rates of mineralization overincubations with mineral salts and trace elements alone, with the greatest effectbeing observed from an addition of (NH4)2SO4. Subsequent incubations with(NH4)2SO4, KNO3, and NH4NO3 revealed that KNO3 was the most favorable forlignin degradation, whereas all three supplements were equally favorable forcellulose degradation. Supplementation with glucose repressed both lignin andcellulose mineralization. The results reported in this study indicate that nitrogenlimitation of wood decomposition may exist in streams of the Pacific Northwest.The radiotracer technique was shown to be a sensitive and useful tool forassessing relative patterns of lignocellulose decay and microbial activity in wood,along with the importance of thoroughly characterizing the experimental systembefore its general acceptance.