Decomposition of (14)C-labeled cellulose substrates in litter and soil from a beechwood on limestone

The decomposition of three different (14)C-labeled cellulose substrates (plant holocellulose, plant cellulose prepared from (14)C-labeled beech wood (Fagus sylvatica) and bacterial cellulose produced by Acetobacter xylinum) in samples from the litter and mineral soil layer of a beechwood on limestone was studied. In a long-term (154 day) experiment, mineralization of cellulose materials, production of (14)C-labeled water-soluble compounds, and incorporation of (14)C in microbial biomass was in the order Acetobacter cellulose > holocellulose > plant cellulose in both litter and soil. In general, mineralization of cellulose, production of (14)C-labeled water-soluble compounds, and incorporation of (14)C in microbial biomass were more pronounced, but microbial biomass (14)C declined more rapidly in litter than in soil. In short-term (14 day) incubations, mineralization of cellulose substrates generally corresponded with cellulase and xylanase activities in litter and soil. Pre-incubation with trace amounts of unlabeled holocellulose significantly increased the decomposition of (14)C-labeled cellulose substrates and increased cellulase activity later in the experiment but did not affect xylanase activity. The sum of (14)CO2 production, (14)C in microbial biomass, and (14)C in water-soluble compounds is considered to be a sensitive parameter by which to measure cellulolytic activity in soil and litter samples in short-term incubations. Shorter periods than 14 days are preferable in assays using Acetobacter cellulose, because the decomposition of this substrate is more variable than that of holocellulose and plant cellulose.