Understanding the changes of natural abundance of stable carbon and nitrogen isotopes (δ13C and δ15N) along soil profile is of great importance in revealing the mechanisms of soil carbon and nitrogen cycling in terrestrial ecosystems. Based on a comprehensive review on the distribution of δ13C and δ15N along soil profile, the mechanisms underlying their vertical distribution were mainly introduced here. There were three mechanisms driving the δ13C vertical distribution in soil profile: 1) historical changes of vegetation δ13C value, 2) changes of C3-C4 species dominance in plant communities, 3) accumulation of 13C-enriched microbial-derived carbon during decomposition. The effects of 13C Suess effect on the vertical distribution of δ13C in soil profile were also discussed. There were four mechanisms underlying the vertical distribution of δ15N in soil profile: 1) 15N-depletion gas loss during denitrification, 2) accumulation of 15N-enriched microbial-derived nitrogen during decomposition, 3) accumulation of 15N-encriched mycorrhizal fungi residues in deep soil as a result of transferring 15N-depleted nitrogen compounds to plants by mycorrhizae, 4) intera-ction between soil organic matter and mineral substance. We proposed important concerning points for the future study on vertical distribution of natural abundance of stable carbon and nitrogen isotopes in soil profile.
土壤碳、氮稳定同位素自然丰度(δ13C和δ15N)随土壤深度变化的研究,对揭示碳、氮元素生物地球化学循环机制具有重要意义。本文在概述土壤剖面δ13C和δ15N垂直分布特征的基础上,重点介绍了土壤δ13C和δ15N垂直分布模式的影响机制。土壤剖面δ13C垂直分布模式的影响机制主要有3种: 1)植被δ13C值的历史变化;2)植物群落C3-C4植物优势度变化;3)分解过程中13C富集的微生物源碳的积累。此外,讨论了13C休斯效应对土壤剖面δ13C垂直分布模式的影响。土壤剖面δ15N垂直分布模式的影响机制主要有4种: 1)反硝化过程产生的15N贫化气体的损失;2)分解过程中15N富集的微生物源氮的积累;3)菌根将15N贫化的含氮化合物转移到植物而在深层土壤积累15N富集的菌根真菌残留物;4)土壤有机质-矿物相互作用。最后提出了未来土壤剖面碳、氮稳定同位素自然丰度的垂直分布模式研究应该关注的重点。.
Keywords: carbon stable isotope; isotopic fractionation; nitrogen stable isotope; soil profile; vertical distribution.