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Climate warming and organic matter decomposition are connected in a recursive manner; this recursion can be described by temperature sensitivity. We conducted a multifactorial laboratory experiment to quantify the temperature sensitivity of organic carbon (C) and nitrogen (N) decomposition processes of common boreal organic soils. We incubated 36 mor and 36 slightly decomposed Carex-Sphagnum peat samples in a constant moisture and ambient temperature for 6 months. The experiment included three temperature and two moisture levels and two food web manipulations (samples with and without fungivore enchytraeid worms). We determined the release of carbon dioxide (CO2) and dissolved organic carbon (DOC) in seven molecular size classes together with ammonium N and dissolved organic N in low molecular weight and high molecular weight fractions. The temperature sensitivity function Q10 was fit to the data. The C and N release rate was almost an order of magnitude higher in mor than in peat. Soil fauna increased the temperature sensitivity of C release. Soil fauna played a key role in N release; when fauna was absent in peat, the N release was ceased. The wide range of the studied C and N compounds and treatments (68 Q10 datasets) allowed us to recognize five different temperature sensitivity patterns. The most common pattern (37 out of 68) was a positive upwards temperature response, which was observed for CO2 and DOC release. A negative downward pattern was observed for extractable organic nitrogen and microbial C. Sixteen temperature sensitivity patterns represented a mixed type, where the Q10function was not applicable, as this does not allow changing the sign storage change rate with increasing or decreasing temperature. The mixed pattern was typically connected to intermediate decomposition products, where input and output fluxes with different temperature sensitivities may simultaneously change the storage. Mixed type was typical for N processes. Our results provide useful parameterization for ecosystem models that describe the feedback loop between climate warming, organic matter decomposition, and productivity of N-limited vegetation. [ABSTRACT FROM AUTHOR]

Mor, slightly decomposed peat and highly decomposed peat, two soil types of each, were incubated for 154 days in the laboratory at +15 °C with and without enchytraeid worms, which functionally are the most influential faunal group in boreal forests. We quantified the release rates of organic and inorganic nitrogen (N) in dissolved and extractable forms from decomposing organic matter and explored the effects of enchytraeid worms on the release rates. About 80% of the dissolved N was released in the form of NH4+-N, except in mor without worms and in slightly decomposed peat with and without worms, where the net release from soil solution was in the form of dissolved organic N (DON). The majority of DON was in the high molecular weight fraction. In the presence of worms, the mineralization rate of N was highest in mor and in the absence of worms in highly decomposed peat. The large initial DON pool may explain the high mineralization rate in highly decomposed peat. The changes in the soil-solution N pool were small compared to the changes in extractable N pool which emphasizes the importance of the adsorbed N in soil N dynamics. Because N release through decomposition is the major component of N balance in forested catchments, the results of the study can be used for improving models of catchment scale N dynamics. [ABSTRACT FROM AUTHOR]

Boreal forests and peatlands compose significant global carbon (C) storage. Decomposition of organic matter plays a key role in global greenhouse gas balance. Decomposition is a complicated process and is regulated by organic matter quality, physical conditions such as temperature, moisture and oxygen supply, nitrogen (N) availability, soil microbes and soil fauna. To reveal these interactions, multifactorial decomposition experiments are needed. We conducted such experiment in laboratory to quantify temperature sensitivity of C and N processes in decomposition of most common boreal organic soils. We incubated 36 mor and 36 slightly decomposed Carex-Sphagnum peat samples in constant moisture and constant ambient temperature for 6 months. The experiment included three temperature and two moisture levels, and two food web manipulations (samples with and without fungivore enchytraeid worms). The release of carbon dioxide (CO2), dissolved organic carbon (DOC) in seven molecular size classes, together with ammonium N and dissolved organic N (DON) in low molecular weight (LMW) and high molecular weight (HMW) fractions were determined. Q10 temperature sensitivity function was fitted to the data. C and N release rate was almost an order of magnitude higher in mor than in peat. Soil fauna increased temperature sensitivity of C release. Soil fauna played a key role in release of N: in absence of soil fauna N immobilized throughout the experiment in peat samples. The wide range of the studied C and N compounds and treatments (68 Q10 -datasets) allowed us to recognize five different temperature sensitivity patterns. The most common pattern (37 out of 68) was a positive upwards temperature response, which was observed e.g. for CO2 and DOC release. Negative downwards pattern was observed for extractable organic nitrogen and microbial C. Sixteen temperature sensitivity patterns represented a mixed type, where Q10-function is not applicable, because Q10 equation does not allow changing the sign of storage change rate within any temperature range. The mixed pattern was typical for intermediate decomposition products of N, in which input and output fluxes with different temperature sensitivities may simultaneously change the storage. The results support the carbon-quality-temperature –hypothesis. [ABSTRACT FROM AUTHOR]