土壤反硝化过程速率测定方法

Methods for measuring soil denitrification rate

土壤反硝化过程是指土壤中的硝酸盐、亚硝酸盐等含氮物质在反硝化微生物的作用下还原成氮气(N_(2))、一氧化氮(NO)、氧化亚氮(N_(2)O)等气体的过程,是氮循环中重要的过程之一.反硝化的中间产物N_(2)O是一种重要的温室气体,其中从土壤中释放的量占地球总排放量的70%.反硝化作用主要由硝酸盐还原酶(nitrate reductase,Nar)、亚硝酸还原酶(nitrite reductase,Nir)、一氧化氮还原酶(nitric oxide reductase,Nor)和氧化亚氮还原酶(nitrous oxide reductase,Nos)所催化,相应的编码基因分别为nar、nir、nor和nos.多种土壤反硝化速率测定方法因技术、设备、实验设计等原因存在不同优缺点,据此在自己的研究中选择合适的方法至关重要.测定土壤反硝化的方法目前主要有乙炔抑制法、^(15)N同位素示踪法、N_(2)直接测定法、硝酸盐消失法、质量守恒法和化学计量法等6种方法.乙炔抑制法,操作简单,但是不适合土壤养分含量低的土壤;^(15)N同位素示踪法测定结果比较精确,但是价格昂贵,成本高;N_(2)直接测定法则需要精密的仪器.今后反硝化过程测定方法的发展不仅是测量方法的改进,也需要注重精密仪器的研发.

Soil denitrification refers to the process of reducing soil nitrate,nitrite,and other nitrogen-containing substances into nitrogen(N_(2)),nitric oxide(NO),and nitrous oxide(N_(2)O)gas catalyzed by denitrifying microorganisms.Denitrification is one of the most important processes in the nitrogen cycle.N2O,an intermediate product of denitrification,is an important greenhouse gas,and its emission from the soil accounts for 70%of the total global emissions.Denitrification is mainly catalyzed by nitrate reductase(Nar),nitrite reductase(Nir),nitric oxide reductase(Nor),and nitrous oxide reductase(Nos),and the corresponding coding genes are nar,nir,nor,and nos,respectively.There are some methods to determine the soil denitrification rate,and each has its specific problems owing to the technique used,equipment,and experimental design.Therefore,it is important to understand the advantages and disadvantages of various methods and select the appropriate method for our study.Currently,the main methods for measuring soil denitrification include(1)the acetylene inhibition method,(2)^(15)N isotope tracer method,(3)direct N_(2) quantification,(4)nitrate disappearance method,(5)mass balance approaches,and(6)stoichiometry approaches.Each method has advantages and limitations.The acetylene inhibition method is cheap and easy to operate;however,it is not suitable for nutrientpoor soil.^(15)N isotope tracer method is accurate but expensive,and direct N_(2) quantification requires sophisticated equipment.The future development of denitrification methods includes the improvement of measurement procedures and the development of precision instruments.