Afforestation has been proposed as an effective method for reducing the atmospheric CO₂ concentration because of the ability to sequester C in vegetation and soil. Despite numerous studies have been conducted to investigate the contribution of afforestation to C sequestration on both regional and global scales, effect of afforestation on soil C accumulation remains a widely debated topic. Furthermore, there was limited information regarding soil N dynamic and C-N interactions, which are very important in determining whether the C sink following afforestation could be sustained over the long term. 

DENG Qi, an assistant research fellow of Wuhan Botanical Garden, under the supervision of Prof. CHENG Xiaoli, conducted a field study in Danjiangkou Reservoir region of central China to evaluate soil C and N dynamics following afforestation by comparing soil organic C and N (SOC and SON), soil net N mineralization and nitrification, and inorganic N concentrations in the plant rhizosphere and open areas in the forest, shrubland and adjacent cropland.  

Study demonstrated that afforestation increased SOC but did not significantly affect SON in the plant rhizosphere. Due to large quantity of low-quality litter (with high C: N ratios) inputs, afforestation enhanced soil C recalcitrant indexes (RIC) but decreased soil N recalcitrance indexes (RIN) in the plant rhizosphere. Both SON and RIN significantly decreased following afforestation in the open areas. Afforestation decreased inorganic N concentrations and net N mineralization. Soil net N mineralization was negatively correlated with soil C: N ratios across land use types.  

These results suggest that afforestation could increase SOC stocks resulting from large low-quality litter input, but over the long-term, this increase is likely limited due to decreased soil N availability. 

This research was financially supported by the National Natural Science Foundation of China and the “Strategic Priority Research Program-Climate Change: Carbon Budget and Relevant Issues” of the Chinese Academy of Sciences. Results have been published in Soil Biology & Biochemistry entitled “Carbon-nitrogen interactions during afforestation in central China”