Effect of nitrogen addition on carbon and nitrogen stable isotopes in temperate forest litter and soil

Abstract

Aim : The aim of this study was to investigate the changes of litter and soil carbon and nitrogen stable isotopes in temperate forest ecosystem under nitrogen addition. Methodology : In a mixed broad-leaf Korean pine forest in Changbai Mountain, China after 6 years of nitrogen addition (50 kg·ha-2·yr-1) treatment, the content of organic carbon and nitrogen, stable isotopes of carbon and nitrogen in litter and soil layer were determined by elemental analyzer and isotope ratio mass spectrometer. Results : The results showed that the carbon concentration decreased with soil depth in the control and treatment samples. The nitrogen concentration had a tendency to increase in the decomposed litter layer. Nitrogen addition did not show significant effect on carbon and nitrogen concentration. The carbon stable isotope (δ13C) was about -27‰ in forest cover layer and organic matter layer, while it was as high as -25.3‰ in mineral soil layer. Nitrogen addition had no significant effect on the value of δ13C. The range of nitrogen stable isotope (δ15N) was -1.6 ∼ 5.5‰, which increased with the depth of soil. δ15N value increased significantly (P = 0.039) in the decomposed litter layer under nitrogen addition. Interpretation : δ15N enrichment implied that more 15N was remaining under nitrogen addition. This indicated that nitrogen deposition enhanced the decomposition of organic matter implied by δ15N enrichment in the decomposed litter layer, although carbon content did not show significant change. This study provides a data support for further studies on the effects of nitrogen deposition on forest ecosystems.