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| Titel |
Litter type affects the activity of aerobic decomposers in a boreal peatland more than site nutrient and water table regimes |
| VerfasserIn |
P. Straková, R. M. Niemi, C. Freeman, K. Peltoniemi, H. Toberman, I. Heiskanen, H. Fritze, R. Laiho |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 9 ; Nr. 8, no. 9 (2011-09-27), S.2741-2755 |
| Datensatznummer |
250006133
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| Publikation (Nr.) |
 copernicus.org/bg-8-2741-2011.pdf |
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| Zusammenfassung |
Peatlands are carbon (C) storage ecosystems sustained by a high water table
(WT). High WT creates anoxic conditions that suppress the activity of
aerobic decomposers and provide conditions for peat accumulation. Peatland
function can be dramatically affected by WT drawdown caused by climate
and/or land-use change. Aerobic decomposers are directly affected by WT
drawdown through environmental factors such as increased oxygenation and
nutrient availability. Additionally, they are indirectly affected via
changes in plant community composition and litter quality. We studied the
relative importance of direct and indirect effects of WT drawdown on aerobic
decomposer activity in plant litter at two stages of decomposition
(incubated in the field for 1 or 2 years). We did this by profiling 11
extracellular enzymes involved in the mineralization of organic C, nitrogen
(N), phosphorus (P) and sulphur. Our study sites represented a three-stage
chronosequence from pristine to short-term (years) and long-term (decades)
WT drawdown conditions under two nutrient regimes (bog and fen). The litter
types included reflected the prevalent vegetation: Sphagnum mosses, graminoids,
shrubs and trees.
Litter type was the main factor shaping microbial activity patterns and
explained about 30 % of the variation in enzyme activities and activity
allocation. Overall, enzyme activities were higher in vascular plant litters
compared to Sphagnum litters, and the allocation of enzyme activities towards C or
nutrient acquisition was related to the initial litter quality (chemical
composition). Direct effects of WT regime, site nutrient regime and litter
decomposition stage (length of incubation period) summed to only about 40 % of the
litter type effect. WT regime alone explained about 5 % of the variation in
enzyme activities and activity allocation. Generally, enzyme activity
increased following the long-term WT drawdown and the activity allocation
turned from P and N acquisition towards C acquisition. This caused an
increase in the rate of litter decomposition. The effects of the short-term
WT drawdown were minor compared to those of the long-term WT drawdown: e.g.,
the increase in the activity of C-acquiring enzymes was up to 120 % (bog)
or 320 % (fen) higher after the long-term WT drawdown compared to the
short-term WT drawdown. In general, the patterns of microbial activity as
well as their responses to WT drawdown depended on peatland type: e.g., the
shift in activity allocation to C-acquisition was up to 100 % stronger at
the fen compared to the bog.
Our results imply that changes in plant community composition in response to
persistent WT drawdown will strongly affect the C dynamics of peatlands. The
predictions of decomposer activity under changing climate and/or land-use
thus cannot be based on the direct effects of the changed environment only,
but need to consider the indirect effects of environmental changes: the
changes in plant community composition, their dependence on peatland type,
and their time scale. |
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