植物选择吸收土壤可溶性有机氮和无机氮的动态变化及机制研究

Nitrogen is one of the macronutrients required for plant growth. Traditional concept of nitrogen nutrition in terrestrial ecosystem has assumed that plant root can not obtain organic nitrogen directly, and organic nitrogen can be used by terrestrial plants only after it is decomposed into inorganic nitrogen. Recent studies have confirmed that plant has the capacity to take up soil soluble organic nitrogen, challenging the traditional concept of nitrogen nutrition.So, the process and mechanism of plant selectivly absorbing soil soluble organic nitrogen and inorganic nitrogen are attracting considerable attention, but progess is still very limited.To solve the above scientific question, quantifing the contribution of soil soluble organic nitrogen to plant is the core. However, the results of most previous studies on the contribution of soil soluble organic nitrogen to plant are questioned by researchers because these experiments which exists man-made interference can not reflect the state of nature, and their calculated values are extremely inconsistent. Natural nitrogen isotope techniques can quantify the contribution of soil soluble organic nitrogen under natural conditions without man-made inference, providing a solution to the problem. This application plans to conduct a joint dynamic study of soil soluble organic nitrogen, inorganic nitrogen and plant nitrogen in soil-plant(Digitaria decumbens) system. By measuring the value of natural abundance of nitrogen isotopes, we will acquire a detailed understanding of the isotopic variation of soil soluble nitrogen and plant nitrogen, and calculate the contribution of soluble organic nitrogen to plant nitrogen by the isotopic equilibrium equation, and further probe into the mechanism of the absorption process. The result of this study will provide an important scientific basis for analysing biogeochemical processes and ecological effects of soil soluble nitrogen in the ecosystem.

氮是植物生长所必需的大量营养元素之一。传统理论认为植物只能直接吸收土壤中的可溶性无机氮，近年的研究表明植物也具有直接获取可溶性有机氮的能力。因此，植物对土壤可溶性有机氮和无机氮选择吸收的过程及机制也随之受到广泛关注，但进展尚十分有限。本项目拟以自然状态下的土壤——植物（俯仰马唐）体系为研究对象，通过对土壤中可溶性有机氮、无机氮以及植物总氮的联合动态研究，掌握三者同位素的动态变化规律，利用同位素方程量化土壤可溶性有机氮对植物总氮的贡献，结合环境因子探讨植物选择吸收土壤可溶性有机氮和无机氮的动态变化机制，为阐析土壤可溶性氮素在生态系统中的生物地球化学过程和生态效应提供重要的科学依据。

土壤氮素是植物氮素的主要来源，本项目按计划采集土壤和植物样品，获得土壤不同形态氮含量和同位素的变化过程数据，探讨了影响土壤氮素变化的过程及机制。认为降水是直接或者间接控制土壤氮素过程的主要因素，主要包括淋滤作用和受降水间接影响的微生物硝化反硝化作用。在少雨季土壤氮素过程可能受微生物驱动的硝化反硝化过程控制；多雨季则受淋滤和微生物驱动的硝化反硝化过程共同影响。获得植物氮含量和同位素的变化过程数据，量化可溶性有机氮对植物总氮的贡献。植物吸收土壤中的可溶性氮素，其氮同位素值明显低于可溶性氮同位素值，表明植物吸收可溶性无机氮的过程发生同位素分馏。项目利用同位素分馏方程估算了土壤可溶性有机氮对植物生长的贡献（5.90—83.61%,平均值为50.06%），推测该过程可能受到土壤可溶性氮素中无机氮和有机氮的比例的影响。综合上述结果，本研究为探讨土壤——植物体系氮过程奠定了工作基础，同时对于认识植物选择吸收土壤可溶性有机氮和无机氮过程提供了启示性线索。项目资助发表论文3篇，另有数据结果正在分析撰写文章，2018年将发表2篇相关论文（至少1篇SCI收录）。项目直接经费25万元，支出18.4827万元，各项支出与预算相符。剩余经费6.5173万元，将用于本项目研究后续支出。