The soil respiration accounts for 30-50% of carbon emission of terrestrial ecosystems. Soil respiration consists of autotrophic respiration and heterotrophic respiration. It is necessary to separate both for estimating the forest carbon cycle as they have different origin and responses to the environment factors.
The 13C pulse labelling technique is suitable to calculate the ratio of autotrophic to soil respiration because this technique can change the isotope ratio of autotrophic respiration artificially by fixing pure 13CO2 with photosynthesis. To estimate the role of autotrophic respiration of black spruce forest on the permafrost where the climate change is ongoing, pulse labelling experiments were conducted and the 13C isotope ratio in soil and root respiration were measured.
The peak of 13C in root respiration was about 6 days after labeling in spring 2016, and 4 days in summer 2015. The ratio of autotrophic respiration to soil respiration was estimated 0-20% around the tree, depends on the distance from the target tree.