Carbon (C)–nitrogen (N) interactions in terrestrial ecosystems regulate climate–C cycle feedbacks. How N additions affect soil C sequestration and then regulate climate change is not fully understood.

Previous studies have assessed effects of N on bulk soil organic C (SOC), but have not yet carefully examined its effects on different SOC fractions, which determine how fast the N-regulated C cycle feeds back to climate.

Researchers from the Institute of Subtropical Agriculture (ISA) of Chinese Academy of Sciences synthesized data from 36 studies with 296 observations by a meta-analysis to evaluate the responses of SOC fractions to N additions.

The team found that the SOC that was separated by density fractionation increased by 18.3% for free light fractions and by 3.0% for heavy density fractions without change in the occluded light fraction under N addition compared with the control.

The SOC that was separated by aggregate fractionation increased by 4.4% for macroaggregate-associated fractions and by 6.5% for aggregate mineral‐associated fractions without change in the microaggregate-associated fraction under N additions.

When bulk SOC was separated by chemical permanganate oxidation, the oxidizable fraction increased by 10.4%, whereas the unoxidizable fraction increased by 4.5%. The changes in different soil C fractions were related to the mechanisms of SOC stabilization.

“Because of the significant increases in non-labile SOC fractions, our findings suggest that on a global scale, increased additions of N might promote SOC accumulation and slow down climate change in the long term” said CHEN Hao, an associate professor at ISA.

These findings will be useful in model development for better prediction of SOC sequestration under N additions.

This work was funded by the Natural Science Foundation of Guangxi Province of China (2017GXNSFAA198038), the National Key Research and Development Program of China (2016YFC0502404), the Chinese Academy of Sciences through its "Light of West China" Program to Hao Chen, the Strategic Priority Research Program of Chinese Academy of Sciences (XDA13010302), and the National Natural Science Foundation of China (31500405).

The study entitled “Different responses of soil organic carbon fractions to nitrogen additions” has been published online in European Journal of Soil Science. This article is available for download at https://doi.org/10.1111/ejss.12716.

Effects of N addition on (a) total SOC pool, (b) SOC fractions separated by the density fractionation method, (c) SOC fractions separated by aggregate fractionation method and (d) SOC fractions separated by oxidation method. (Image by Chen Hao)

Contact: LI Dejun

E-mail: dejunli@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences