The total carbon pool of the earth is 1800Pg C where 1480Pg C exists as organic matter and dead plant parts (litters) and 45% consisted by forest. A little change in soil organic C may cause significant change in atmospheric CO₂ concentration.

So the dynamics of Soil carbon pool of forest ecosystem has become one of a key factor in assessment of carbon budget of the global terrestrial ecosystem on the background of global changes and dealing with the coming global climate crises. 

Since the industrial revolution, the use of fossil fuel and the increase in intensive agricultural production has induced in rapid increase in active N release into atmosphere.

Correspondingly, the atmospheric N deposition rapidly increase also and in some region, N saturation has appeared. Recent years, along with the advancement in the research work, it is realized that N cycling is a key factor in terrestrial ecosystem C budget and global change.

The effects of variation in precipitation and N deposition on the C capture ability of soil has become a hot spot in the investigation on global C budget. 

Prof. ZHANG Junhui from Institute of Applied Ecology, Chinese Academy of Sciences, led his group and Dr. CHEN Zhijie take the typical Changbai Mountain forest plots that had treated with successive six years N addition as materials investigated the variation of the stability of soil organic C pool by field observation and laboratory incubation.  

The results show that in contrast to the zero control and low dose (25kg N ha^-1 yr^-1) addition, the long-term high dose N (25 kg N ha^-1 yr^-1) addition resulted in the increase in soil C pool stability.

The rate of soil C release was 30% lower than control. The mechanism is the increase in the protection of macro-aggregates on micro-aggregates and the enhancement in the resistance of soil organic matter to decomposition (use δ13C as an indicator).  

The results were published in European Journal of Soil Science entitled "Addition of nitrogen enhances stability of soil organic matter in a temperate forest.

The work was supported by CAS Pilot program, National Natural Science Foundation of China.