Quality of DOC produced during litter decomposition of peatland plant dominants

Litter decomposition is an important source of dissolved organic matter (DOC). In peatlands with hardly degradable soil DOC, the input of DOC from vascular plant litter can represent an important source of nutrients and decomposable substrates for soil microorganisms. We established a laboratory incubation with the litters of three peatland plant dominants (Sphagnum fallax, Vaccinium myrtillus and Eriophorum vaginatum) for 200 days, aiming to study DOC production and its quality. The quality of the DOC leached from the litters was characterized by a distribution of C, N and P among molecular weight (MW) fractions (< 1, 1-10, 10-100 and > 100 kDa), their aromaticity, composition of low molecular weight compounds (organic acids, sugars and amino acids) and DOC biodegradability. The leaves of vascular plants decomposed the fastest, releasing larger amounts of nutrients and easily degradable organic acids, sugars and amino acids to the leachate, when compared to their roots and Sphagnum. DOC distribution to the MW fractions did not differ among the litters. Neither the DOC distribution to the respective fractions nor leachate C/N/P stoichiometry were factors driving DOC biodegradability. Total dissolved P distribution to the MW fractions significantly differed among the litters, with Sphagnum being very specific: P was initially associated only with high molecular weight DOC, while later it was redistributed to the lower MW fractions and complexed with Al and Fe. The complexation may retard soluble reactive P leaching especially from Sphagnum litter. DOC biodegradability was higher for the vascular plant leaf litter than for the Sphagnum litter in the early stages of decomposition (20 days) but later decreased and became more uniform for all litters. These temporal differences (by decomposition stage) were more pronounced than those caused by litter origin. Our results indicate that mainly leaf litter of vascular plants can release significant amounts of DOC during the early stage of decomposition. This DOC is more aromatic with higher biodegradability and more nutrients (especially P) as compared to Sphagnum and can thus temporarily stimulate microbial activity in habitats dominated by the vascular plants.