13C PLFAs: a key to open the soil microbial black box?

Phospholipid fatty acid (PLFA) analysis is an effective non-culture-based technique for providing information on the living soil microbial community. The coupling of C-13 tracers with PLFA analysis can indicate the response of microbial populations to environmental change and has been widely used to trace C flux in soil-plant systems. Based on studies applying C-13 PLFA analysis, the current technological status, current applications and future opportunities are discussed and evaluated. First we describe some aspects of the labelling and analytical methodology. The approaches to study the incorporation of C-13 substrate and rhizodeposition C into soil microbial communities are compared. We continue with the application of C-13-labelling to study soil microbial communities, including the utilization of soil mineralisation products, the C flux from plants into the soil microbial pool, the biodegradation of pollutants and on the application to a specific microbial group, i.e. methanotrophs. Additionally, some perspectives on the limitations of the C-13 PLFA method and future research avenues are noted. Although including some limitations and complications, the C-13 PLFA method provides an excellent tool for understanding the relationship between microbial populations and soil biogeochemical cycling, thus providing a key to open the soil microbial black box.