Soil carbon stability and temperature sensitivity of carbon decomposition along an elevation gradient in the Changbai Mountain, China

Background/Question/Methods

Forest soils at high altitude are expected to store larger quantities of organic carbon (C) and to be more temperature sensitive than that at lower altitude. However, understanding of the temperature sensitivity (Q₁₀) of soil C decomposition is still limited, which limits our ability to predict accurately how soil C storage and cycling would respond to global warming. Here we investigated the stability of soil C pools and their corresponding decomposition Q₁₀ simultaneously in O-layer material and mineral soil along an elevation gradient. We divided soil C pool into three C components (active, slow, and acid-resistant C pools) and their sizes were determined by an acid hydrolysis-incubation method. Based on these values, Q₁₀ of active and slow C decomposition was determined by comparing the times required to respire all C of each pool at two different temperatures during the incubation period.

Results/Conclusions

Results show that: (1) Carbon content in bulk soil (17.9-46.6 g kg^-1 from 800 to 1800m) and acid-resistant pool (10.5-24.8 g kg^-1) in mineral soil increased with increasing elevation, while these variables in O-layer material was not influenced by altitude. (2) Altitude effects on soil respiration rate and Q₁₀ of bulk soil were different in O-layer material and mineral soil. (3) Soil respiration rate in mineral soil increased with increasing altitude at both 15°C (14.7-47.8 µg CO₂-C g^-1 soil d^-1 from 800 to 1800m, average values of the sampling times) and 25°C (29.5-105.4 µg CO₂-C g^-1 soil d^-1), but no altitude effect on Q₁₀ of bulk soil in mineral soil (1.91-2.17, P > 0.05) was observed. These findings suggested that in temperate forest with organic forest floor, O layer should be considered separately from the mineral layer when studying soil C stability because they had distinct responses to temperature. Q₁₀ of active and slow C decomposition was also different, which partially explained the conflicts observed in previous studies of bulk soil C decomposition Q₁₀. Our methods provided a novel approach to study temperature sensitivity of soil C decomposition for better understanding soil C stability and its responses to global warming.