Litter quality and its response to water level drawdown in boreal peatlands at plant species and community level

Abstract

Changes in the structure of plant communities may have much more impact on ecosystem carbon (C) cycling than any phenotypic responses to environmental changes. We studied these impacts via the response of plant litter quality, at the level of species and community, to persistent water-level (WL) drawdown in peatlands. We studied three sites with different nutrient regimes, and water-level manipulations at two time scales. The parameters used to characterize litter quality included extractable substances, cellulose, holocellulose, composition of hemicellulose (neutral sugars, uronic acids), Klason lignin, CuO oxidation phenolic products, and concentrations of C and several nutrients. The litters formed four chemically distinct groups: non-graminoid foliar litters, graminoids, mosses and woody litters. Direct effects of WL drawdown on litter quality at the species level were overruled by indirect effects via changes in litter type composition. The pristine conditions were characterized by Sphagnum moss and graminoid litters. Short-term (years) responses of the litter inputs to WL drawdown were small. In longterm (decades), total litter inputs increased, due to increased tree litter inputs. Simultaneously, the litter type composition and its chemical quality at the community level greatly changed. The changes that we documented will strongly affect soil properties and C cycle of peatlands.

Biochemical determinants of litter quality in 15 species of Sphagnum

“…holocellulose and lignin-like phenolics. However, we identified such a trade-off in litters of the 8 Sphagnum species presented by Straková et al (2010). Since we expected the summed weight of HC and total KL to give almost 100% of the initial litter, our results (ranging between −16 and +4%) raised a question of reliability of the two gravimetric analytical methods for bryophytes.…”

“…Lower chemical stability of KL after acidolysis in species of sect. Cuspidata was reported by Straková et al (2010). We introduced dev100 because our results revealed no trade-off in production between the two main components of Sphagnum cell walls, i.e.…”

“…Cuspidata (−9%) may be the result of greater degradation of HC, perhaps of the easily hydrolysable hemicelluloses (Kumar et al 2013) rather than the highly resistant cellulose microfibrils or sphagnan (sphagnan was not depleted in Cuspidata during holocellulose extraction as shown by a constant ratio of litter-derived CEC and holocellulose-derived sphagnan). Litters in the study of Straková et al (2010) had dev100 between −13 and −17% in sections Sphagnum+Cuspidata and Acutifolia, respectively. Here, the difference between sections could be explained by hot-water extractives (4-8%).…”

“…In the first supernatants, we measured dissolved phenolics, i.e. soluble Klason lignin (following Ehrman 1996) as the polymeric phenolics of Sphagnum are prone to dissolve by acid hydrolysis (Farmer and Morrison 1964;Straková et al 2010). A sample of the supernatant was diluted 36 times with 2.48% sulphuric acid and its absorbance at 205 nm was measured spectrophotometrically.…”

Greenhouse gas flux measurements in a forestry-drained peatland indicate a large carbon sink

“…There is also an increase in the input of slow decomposing woody and moss litter and a decrease in the input of fasterdecomposing grasses and herbs (Laiho et al, 2003). Furthermore, the quantity of the aboveground litterfall increases dramatically after the drainage which may compensate or even exceed the decomposition of the old C in the peat (Straková et al, 2010(Straková et al, , 2011. In addition, part of the C released from the decayed litter is translocated as a solute to deeper peat layers and contributes to the C accumulation in the peat (Domisch et al, 2000).…”