Disentangling direct and indirect effects of water table drawdown on above‐ and belowground plant litter decomposition: consequences for accumulation of organic matter in boreal peatlands

Abstract

Pristine peatlands are carbon (C)-accumulating wetland ecosystems sustained by a high water table (WT) and consequent anoxia that slows down decomposition. Persistent WT drawdown as a response to climate and/or land-use change affects decomposition either directly through environmental factors such as increased oxygenation, or indirectly through changes in plant community composition. This study attempts to disentangle the direct and indirect effects of WT drawdown by measuring the relative importance of environmental parameters (WT depth, temperature, soil chemistry) and litter type and/or litter chemical quality on the 2-year decomposition rates of above-and belowground litter (altogether 39 litter types). Consequences for organic matter accumulation were estimated based on the annual litter production. The study sites were chosen to form a three-stage chronosequence from pristine (undrained) to short-term (years) and long-term (decades) WT drawdown conditions at three nutrient regimes. The direct effects of WT drawdown were overruled by the indirect effects through changes in litter type composition and production. Short-term responses to WT drawdown were small. In long-term, dramatically increased litter inputs resulted in large accumulation of organic matter in spite of increased decomposition rates. Furthermore, the quality of the accumulated matter greatly changed from that accumulated in pristine conditions. Our results show that the shift in vegetation composition as a response to climate and/or land-use change is the main factor affecting peatland ecosystem C cycle, and thus dynamic vegetation is a necessity in any model applied for estimating responses of C fluxes to changing environment. We provide possible grouping of litter types into plant functional types that the models could utilize. Furthermore, our results clearly show a drop in soil summer temperature as a response to WT drawdown when an initially open peatland converts into a forest ecosystem, which has not yet been considered in the existing models.

Effects of nitrate and sulfate on greenhouse gas emission potentials from microform-derived peats of a boreal peatland: A 13C tracer study

“…In vitro conditions strongly decreased limitations of fluctuating natural environmental factors, thereby revealing the differences in the constituent soil properties. Therefore, under controlled conditions, i) the type and abundance of decomposers (Basiliko et al, 2007;Strakova et al, 2012), and consequently ii) the quality and quantity of the substrate they are decomposing (Moore and Dalva, 1997;Yavitt et al, 2000;Blagodatskaya et al, 2010;Strakova et al, 2012) become the main determinants of CO 2 fluxes among the microforms. Thus, the MBC explained ca.…”

Phylogenetic or environmental control on the elemental and organo-chemical composition of Sphagnum mosses?

“…Right panel shows the correlation between the PC axes and the carbohydrate monomers (black arrows) and those supplementary variables (grey arrows) with a correlation coefficient ≤ −0.4 or ≥ +0.4 with PC1 and/or PC2 concentrations in hollow species from the peatland centre potentially reflects the lower nutrient retention capacity of hollows (Bragazza et al 2004), the prevailing direction of water flow and dissolved nutrients from hollows to lawns and hummocks in more continental climates (Eppinga et al 2010) or, alternatively, extra nutrient relocation from deeper depths by co-occurring vascular plant species in lawns and hummocks (Malmer et al 1992;Malmer et al 2003). As nutrient concentrations in Sphagnum plant material co-determine its degradability and speed of mineralisation (Damman 1988;Limpens and Berendse 2003;Straková et al 2012), differences in nutrient concentrations in Sphagnum may have direct implications for mineralisation rates and nutrient cycling in peatlands.…”

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).…”