Decomposition of Carex and Sphagnum litter in fens: Effect of litter quality and inhibition by living tissue homogenates

Decomposition of fresh litter of Carex diandra, originating from a base-rich fen, and Sphagnum fallax, originating from a base-poor fen, was investigated in field experiments with litter bags and laboratory experiments with aerobic incubators. The Carex litter decomposed significantly faster than the Sphagnum litter in all experiments. Further, both litter types decomposed faster in the base-rich than in the base-poor fen. The addition of a small amount of homogenized S. fallax capitulums to litter of both types in the laboratory experiments significantly slowed down the rate of weight loss. The addition of homogenized C. diandra leaves did not influence the decay rate. These results suggest that the slow litter decomposition in Sphagnum-dominated mires is due to the chemical composition of the litter itself and the antibiotic effect of a substance leaching from living Sphagnum cells. Literature on the biochemistry of Sphagnales suggests that ‘Sphagnum acid’, a phenolic compound found in all Sphagna tested, is responsible for these differences.