Search

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., Competing Interests: The authors have declared that no competing interests exist.

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]