Abstract：
Nitrogen (N) cycle is one of the most significant biogeochemical cycles driven by soil microorganisms on the earth. Exogenous humic substances (HS), which include composted-HS and artificial-HS, as a new soil additive, can improve the water retention capacity, cation exchange capacity and soil nutrient utilization, compensating for the decrease of soil HS content caused by soil overutilization. This paper systematically reviewed the contribution of three different sources of HS in the soil-plant system and explained the mechanisms of N transformation through physiological and biochemical pathways. HS convert the living space and living environment of microorganisms by changing the structure and condition of soil. Generally, HS can fix atmospheric and soil N through biotic and abiotic mechanisms, which improved the availability of N. Besides, HS transform the root structure of plants through physiological and biochemical pathways to promote the absorption of inorganic N by plants. The redox properties of HS participate in soil N transformation by altering the electron gain and loss of microorganisms. Moreover, to alleviate the energy crisis and environmental problems caused by N pollution, we also illustrated the mechanisms reducing soil N2O emissions by HS and the application prospects of artificial-HS. Eventually, a combination of indoor simulation and field test, molecular biology and stable isotope techniques are needed to systematically analyze the potential mechanisms of soil N transformation, representing an important step forward for understanding the relevance between remediation of environmental pollution and improvement of the N utilization in soil-plant system.
摘要：
氮（N）循环是地球上由土壤微生物驱动的最重要的生物地球化学循环之一。外源性腐殖质（HS），其中包括堆肥HS和人工HS，作为一种新的土壤添加剂，可以提高保水能力，阳离子交换能力和土壤养分利用，弥补了土壤过度利用导致的土壤HS含量下降。本文系统综述了三种不同来源的HS在土壤-植物系统中的贡献，并解释了通过生理和生化途径转化氮的机制。HS通过改变土壤的结构和状况来改变微生物的生存空间和生存环境。一般来说,HS可以通过生物和非生物机制固定大气和土壤氮，这提高了N的可用性。此外，HS通过生理生化途径改造植物的根系结构，促进植物对无机氮的吸收。HS的氧化还原特性通过改变微生物的电子得失参与土壤N的转化。此外，为了缓解N污染带来的能源危机和环境问题,阐述了HS降低土壤N2O排放的机理以及人工HS的应用前景。最终,室内模拟和现场测试相结合，需要分子生物学和稳定同位素技术来系统分析土壤N转化的潜在机制，代表了理解环境污染修复与改善土壤-植物系统中氮利用之间相关性的重要一步。
