Soil carbon pool is one of the largest carbon pools in terrestrial ecosystems and plays an important role in the study of global carbon cycle and global change. Changes in labile carbon inputs (quantity and quality) are an important manifestation of the current global change. On the one hand, labile carbon can stimulate the mineralization of soil organic carbon (priming effect), on the other hand, it can be utilized by microorganisms to form new soil organic carbon, thus affecting soil carbon balance. 

Under the guidance of Prof. LIU Feng, LIAO Chang, from the Global Change Ecology Group of Wuhan Botanical Garden, took the soil of Badagongshan as the research object in subtropical forest, conducted incubation experiments of adding labile carbon and nitrogen in the surface soil and subsoil, and analyzed the process of "old" carbon mineralization and "new" carbon sequestration in the soils.  

The results showed that the addition of labile carbon promoted the mineralization of soil organic carbon and produced positive priming effect. The priming effect decreased with the increase of nitrogen availability.

The increase of nitrogen availability and the decrease of priming intensity were related to the increase of carbon utilization efficiency of microorganisms, not the enzyme activities. The sequestration efficiency of labile carbon in deep soil was significantly higher than that in surface soil (48% vs 43%), and the "new" carbon in deep soil was more distributed in carbon components with high stability. 

This study was supported by the National Natural Science Foundation of China. Relevant results were recently published as two papers in the Journals of Forestry Research entitled “Nitrogen availability regulates deep soil priming efectby changing microbial metabolic efciency in a subtropical forest” and PeerJ entitled  entitled “Higher carbon sequestration potential and stability for deep soil compared to surface soil regardless of nitrogen addition in a subtropical forest”. 

Structural equation modeling assessing direct and indirect effects of N availability on PE. Numbers adjacent to arrows indicate the effect size of the path coefficient; arrow width is proportional to the magnitude of the relationship. Black solid and dashed arrows indicate positive and negative relationships, respectively. Grey arrows indicate insignificant relationships. Significance levels are: **p< 0.01; *p <0.05; ·p<0.07 (Image by LIAO Chang) 

Principal Component Analysis (PCA) of the distribution patterns of new and native C in surface soil and deep soil. Square represents the surface soil and circle represents the deep soil. Hollow and black solid denotes new C under Glu and Glu+N treatments, respectively, and gray solid denotes native C. The results of PERMANOVA show the effects of soil depth and N addition on the new C distribution pattern (Image by LIAO Chang)