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

Abstract

The Biolog assay is a popular tool for estimating carbon (C) substrate utilization potentials of microbial communities of natural habitats, but its ecological relevance has been questioned. In this study, impacts of simple and complex C substrates on microbial community Biolog activities were assessed to determine if the resulting utilization potentials reflected the amended substrates. A silt loam soil was amended on an equal C-basis with glucose, cellulose, lignin, hydroxyproline, gelatin, or residues from either triticale ( 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 following incorporation of each substrate to soil. In addition, microbial biomass C (MB C) and community fatty acid methyl ester (FAME) profiles were determined at each sampling point to assess community size and structure. Soil amended with lignin maintained similar levels of MB C, Biolog activities, and FAME profiles relative to a non-amended control soil. Soil amended with glucose had higher MB C levels relative to non-amended soil and soils amended with cellulose, lignin, and plant residues. Communities from glucose-amended soil utilized Biolog carbohydrates at high rates but exhibited low utilization potentials for amino acids and polymers. Principal components analysis of FAME data revealed greater amounts of fungal markers in soil amended with glucose during the first 21 days of the incubation. In contrast, soils amended with plant residues had relatively high Biolog activities for all three types of substrates and contained a greater diversity of FAMEs compared to communities from the glucose treatment. Hydroxyproline and gelatin amendments had the greatest impact on the microbial parameters measured. Highest values for MB C, Biolog activity, FAME richness, and diversity were found in either or both treatments at most sampling dates. Biolog polymer utilization was particularly elevated in soil amended with gelatin, which was similar in structure to the Biolog polymer collagen. Positive impacts of hydroxyproline and gelatin on microbial communities may be due to the N content of these treatments; however, triticale and winter pea residues had very similar impacts on soil communities, despite winter pea legume having 1.5 times more N compared to the triticale residue. Together, the Biolog and FAME data revealed successional patterns in microbial communities over time. For example, an increase in carbohydrate utilization in cellulose-amended soil at day 49 corresponded to increases in FAME richness and diversity, with elevated amounts of the fungal fatty acids 18:1ω9 c and 18:3ω6 c detected in this soil.