Sensitivity of soil organic matter decomposition to temperature at different depths in permafrost regions on the northern Qinghai‐Tibet Plateau

Abstract

The temperature sensitivity coefficient (Q10) of soil organic matter decomposition is an important variable for global climate models. Permafrost regions contain large organic carbon pools. A deep core was taken in permafrost from the northern Qinghai‐Tibet Plateau (QTP) and exposed to increases in temperature below and above 0°C. The production of CO2 was related to the soil organic carbon (SOC) contents and stable carbon isotopes. Smaller values of δ13C‐SOC and δ13C‐CO2 showed that the release of CO2 was primarily from soil with large SOC contents. The sensitivities of soil organic matter (SOM) decomposition to temperature near to the permafrost table and in some permafrost layers were larger than those in other layers. In some layers, a temperature increase below 0°C had a greater effect on the decomposition of SOM than one above 0°C. The values of Q10 in active layers varied from 2.7 to 23.0, with a mean of 8.8. The values of Q10 were larger in the deeper layers; they varied from 1.6 to 49.4, with a mean of 20.8. This is because the degradation of permafrost is usually associated with an increase in temperature even when the soil is in a frozen state. Our results suggest that the large values of Q10 at depth under frozen conditions merit more consideration of the response of SOC to climate warming in future research. Highlights The sensitivity to temperature coefficient, Q10, is an important property for global climate models. The values of Q10 for soil organic matter decomposition were also large in deep layers. A temperature increase below 0°C has large effects on Q10. The large values of Q10 at depth under frozen conditions merit more consideration.

Permafrost collapse shifts alpine tundra to a carbon source but reduces N2O and CH4 release on the northern Qinghai‐Tibetan Plateau

“…High N 2 O flux in our study area is partially attributable to the relative high soil nitrogen contents (about 1.5% in the upper 50 cm soils) [ Mu et al, ], which is often associated with N 2 O flux [ Velthof et al, ]. The 61% increase in N 2 O flux from exposed patches could be due to the fact that thermokarst formation simultaneously increases biodegradable nitrogen [ Darrouzetnardi and Weintraub , ; Harms et al, ; Tanski et al, ] and creates heterogeneous redox conditions where coupled nitrification‐denitrification can occur [ Abbott and Jones , ].…”

Greenhouse gas released from the deep permafrost in the northern Qinghai-Tibetan Plateau

“…Temperature is one of the important controls of organic matter decomposition 6 . In this study, greenhouse gas emissions increased with temperature during both the aerobic and anaerobic incubations.…”

“…Based on these findings, the potential release of greenhouse gas via the decompositions of SOM in the QTP can be inferred to be similar to that of high-latitude permafrost regions, although the QTP has lower SOM contents than those in circum-Arctic regions 28 . However, there have been considerable changes in the emissions of greenhouse gas in the QTP, indicating that factors such as temperature 6 , 17 , 29 , soil water content 30 and the chemical characteristics of the SOM 31 play important roles in the emission of greenhouse gas in permafrost regions. Future studies are needed to determine the quantitative relationships between these factors and greenhouse gas emissions.…”

“…In the past decades, permafrost degradation accompanying climate warming has been widely detected in mountain permafrost regions as well as in the high-latitude Arctic regions. This degradation is evident from the deepening of the active layer thickness 2 , 3 , ground temperature increases 4 , 5 , and thermokarst terrain formations 6 . Permafrost thaws accelerate the rates of carbon and nitrogen released by the soil into the atmosphere and cause a significant positive climate-change feedback 7 .…”

“…The soil respirations in the upper soils, such as the upper 10 cm, has been shown to vulnerable to decomposition and to have a high sensitivity to temperature 17 . However, few studies have been performed to determine the CO 2 emissions of the deep permafrost on the QTP 6 . Furthermore, the deep permafrost produces unknown amounts of CH 4 and N 2 O, which are also important greenhouse gases that can be released into the atmosphere 7 .…”