Degradation of 13C–U–Glucose in Sphagnum majus Litter Responses to Redox, pH, and Temperature

Abstract

We studied the utilization of 13C–U–glucose by the microbial community in shallow Sphagnum majus (Russ.) C. Jens. ssp. norvegicum Flatb. litter and its regulation by pH, temperature, and redox conditions. The transformation of 13C–glucose was monitored by solution‐ and solid‐state 13C–nuclear magnetic resonance (NMR) spectroscopy. The aerobic microbial community used the glucose C for respiration and, to a lesser degree, for storage as mannitol, triglycerides, and polysaccharides. Under both aerobic and anaerobic conditions, the allocation of glucose C for storage was greater at pH 6.8 than at 4.3; however, the amount of C used for building new biomass was the same at both pH settings. At 15°C, 15 to 18% of the utilized C under aerobic conditions was found in new microbial biomass: less than the previously reported values of 40 to 72%. This indicates that peat soils may promote significantly different microbial growth patterns from other minerogenic and moor humus soils. The production of mannitol and triglycerides suggests that fungi dominated the microbial community and utilized the glucose under aerobic conditions. Using a combination of solid and liquid NMR techniques we were able, for the first time, to follow the anaerobic pathways of glucose degradation in a natural soil sample. The anaerobic microbial community produced mainly volatile fatty acids (VFA), ethanol, and CO2 from the added glucose, and only minor amounts were converted to methane, storage C, and new microbial biomass. Nuclear magnetic resonance spectroscopy allows nondestructive assays of metabolic events and, therefore, was shown to be an excellent tool for studying the microbial utilization of 13C–glucose in peat.