Application of stable isotope techniques in studies of carbon and nitrogen biogeochemical cycles of ecosystem

Stable isotope techniques have been proved useful as tools for studying the carbon (C) and nitrogen (N) biogeochemical cycles of ecosystem. This paper firstly introduced the basic principles and the distribution characteristics of stable isotope, then reviewed the recent advances and applications of stable isotope in the C and N biogeochemical cycles of ecosystem. By applying the ¹³C natural abundance technique, ecologists are able to understand the photosynthetic path and CO₂ fixation of plants, the CO₂ exchange and C balance status of ecosystem, the composition, distribution and turnover of soil organic C and the sources of organic matter in food webs, while by using the ¹³C labeled technique, the effects of elevated CO₂ on the C processes of ecosystem and the sources and fate of organic matter in ecosystem can be revealed in detail. Differently, by applying the ¹⁵N natural abundance technique, ecologists are able to analyze the biological N₂-fixation, the N sources of ecosystem, the N transformation processes of ecosystem and the N trophic status in food webs, while by using the ¹⁵N labeled technique, the sources, transformation and fate of N in ecosystem and the effects of N input on the ecosystem can be investigated in depth. The applications of both C and N isotope natural abundance and labeled techniques, combined with the elemental, other isotope (³⁴S) and molecular biomarker information, will be more propitious to the investigation of C and N cycle mechanisms. Finally, this paper concluded the problems existed in current researches, and put forward the perspective of stable isotope techniques in the studies on C and N biogeochemical cycles of ecosystem in the future.