Does the chemical nature of soil carbon drive the structure and functioning of soil microbial communities?

The transformation of organic amendments (OA) in soil is in large part performed by soil microbial communities. These processes are strongly affected by the carbon composition of the OAs. We examined microbial community responses to three types of OA: green waste, composted green waste and pyrolysed green waste added to two contrasting agricultural soils. We investigated the relationship between the soil carbon composition (as determined by 13C-solid state NMR), microbial community composition (as determined by phospholipid fatty acid analysis) and microbial activity (as determined by soil enzyme assays). We found that alkyl-C, O-aryl-C, aryl-C and carbonyl-C were able to explain most of the variations (≥50%) in soil microbial community composition and activity. Aryl-C content (reflecting relatively stable carbon forms) strongly influenced microbial composition, while carbonyl-C content (reflecting relatively labile carbon forms) strongly influenced the microbial activity. Our results confirm that there is a tight relationship between carbon composition and soil microbial community composition and function. Results are discussed in the context of examining the relationship between carbon forms, microbial community composition and activity following the addition of different OAs to the soil.