Shifts in substrate utilization potential and structure of soil microbial communities in response to carbon substrates

The Biolog assay is a popular tool for estimating carbon (C) substrate util ization potentials of microbial communities of natural habitats, but its ec ological relevance has been questioned. In this study, impacts of simple an d complex C substrates on microbial community Biolog activities were assess ed to determine if the resulting utilization potentials reflected the amend ed substrates. A silt loam soil was amended on an equal C-basis with glucos e, cellulose, lignin, hydroxyproline, gelatin, or residues from either trit icale (X Triticosecale Wittmack) or Austrian winter pea (Pisum sativum L.) and incubated for 80 days. Mean utilization of Biolog carbohydrates, amino acids, and polymers were determined at 3, 7, 21, 35, 49 and 80 days followi ng incorporation of each substrate to soil. In addition, microbial biomass C (MBC) and community fatty acid methyl ester (FAME) profiles were determin ed at each sampling point to assess community size and structure. Soil amen ded with lignin maintained similar levels of MBC, Biolog activities, and FA ME profiles relative to a non-amended control soil. Soil amended with gluco se had higher MBC levels relative to non-amended soil and soils amended wit h cellulose, lignin, and plant residues. Communities from glucose-amended s oil utilized Biolog carbohydrates at high rates but exhibited low utilizati on potentials for amino acids and polymers, Principal components analysis o f FAME data revealed greater amounts of fungal markers in soil amended with glucose during the first 21 days of the incubation. In contrast, soils ame nded with plant residues had relatively high Biolog activities for all thre e types of substrates and contained a greater diversity of FAMEs compared t o communities from the glucose treatment. Hydroxyproline and gelatin amendm ents had the greatest impact on the microbial parameters measured. Highest values for MBC Biolog activity, FAME richness, and diversity were found in either or both treatments at most sampling dates. Biolog polymer utilizatio n was particularly elevated in soil amended with gelatin, which was similar in structure to the Biolog polymer collagen. Positive impacts of hydroxypr oline and gelatin on microbial communities may be due to the N content of t hese treatments; however, triticale and winter pea residues had very simila r impacts on soil communities, despite winter pea legume having 1.5 times m ore N compared to the triticale residue. Together, the Biolog and FAME data revealed successional patterns in microbial communities over time. For exa mple, an increase in carbohydrate utilization in cellulose-amended soil at day 49 corresponded to increases in FAME richness and diversity, with eleva ted amounts of the fungal fatty acids 18:1 omega 9c and 18:3 omega 6c detec ted in this soil. (C) 2001 Elsevier Science Ltd. All rights reserved.