Chamber measured soil respiration: A useful tool for estimating the carbon balance of peatland forest soils?

Peatlands drained for forestry have a high potential for CO2 emissions due to peat decomposition. Accurate estimates of either these emissions or soil carbon balances (ΔCsoil) on large areas are needed for national greenhouse gas inventories and as input for earth system models. The measurement of forest floor respiration (Rfloor) or heterotrophic soil respiration (Rhet) by portable chambers offers an affordable tool for extensive studies. So far, the reliability of respiration chamber based calculations of ΔCsoil has not been tested and the prerequisites for their use have not been discussed. However, the method is being used in greenhouse gas inventories.In this study, we compared the results of two chamber based methods against a reference estimate based on eddy covariance measurements. In the first method, ΔCsoil was calculated by subtracting Rhet from the litter input into the soil. In the second method, Rfloor was subtracted from the entire allocation of carbon (C) into the soil. A four-year detailed dataset of C dynamics of a drained peatland forest in southern Finland served as the test material.The Rhet method produced results close to those of the reference method, but the results were sensitive to the choice of root turnover rates used in the estimation of litter input. The Rfloor method resulted in a clear underestimation of soil C sink: the accurate estimation of the large photosynthesis and respiration fluxes needed for the calculation turned out to be difficult.In our opinion, the Rhet method could be used to identify hot spots of forest soil CO2 emissions and for balance estimation for large areas. Further development of models for estimating the photosynthesis and respiration fluxes is needed for the application of the Rfloor method. As the estimation of ΔCsoil by subtracting C output from C input is inherently sensitive to bias in the estimation of the input and output, the accuracy of both methods needs further testing with extensive datasets.

► Chamber measured respiration is a useful tool for estimating forest soil C balance. ► Hot spots of CO2 emission can be identified. ► The method is also applicable for estimations on large areas or country level. ► Balance calculation of this kind is sensitive to bias in respiration and C input.