DECOMPOSITION AND BIOMASS INCORPORATION OF C-14-LABELED GLUCOSE AND PHENOLICS IN TAIGA FOREST FLOOR - EFFECT OF SUBSTRATE QUALITY, SUCCESSIONAL STATE, AND SEASON

Forest floor samples from early. intermediate and mature successional sites in the taiga of interior Alaska were exposed to C-14-labeled glucose and two phenolic acids. Our results indicate that microbes present in the taiga forest floor metabolized phenolics. At all sites, biomass incorporation of glucose as measured by the fumigation extraction technique was approximately twice that for the phenolics, while respiration of (CO2)-C-14 was significantly higher for the phenolic compounds. Major differences in C-14 allocation were seen even between phenolic compounds with similar structures. Despite large differences in litter and forest floor composition, the metabolism of our model compounds varied only slightly between successional stages. Seasonal and successional effects were considerably less than those arising from substrate quality with variation greater in the uplands (where succession is fire-dominated) than in the floodplains (where river erosion and deposition are the controlling factors). Any physiological variation in microbial communities through succession must therefore be in organisms which produce exoenzymes that break down primary polymers, rather than in organisms and pathways that use the monomer breakdown products.