摘要
Reactive nitrogen(Nr)emission from soils,e.g.,nitrous acid(HONO)and nitric oxide(NO),is a key process of the global nitrogen(N)cycle and has significant implications for atmospheric chemistry.To understand the underlying mechanisms of soil Nr emissions,air-dried or oven-dried soils are commonly used in the laboratory.To date,few studies have compared the effects of different drying methods on soil Nr gas fluxes and N fractions.Here,the authors studied soil water content,pH,(in)organic N content,and Nr gas fluxes of air-dried,freeze-dried,oven-dried,and fresh soils from different land-use types.The results showed that the soil pH of air-dried and oven-dried samples was significantly lower compared with fresh soil from farmland and grassland,but higher compared with forest soil.The difference in soil pH between freeze-dried and fresh soil(mean±standard deviation:0.52±0.31)was the lowest.In general,all drying methods increased the soil NH4+-N,NO3−-N,and dissolved organic N contents compared with fresh soil(P<0.05).The maximum HONO and NO flux and total emissions during a full wetting–drying cycle of fresh soil were also increased by air-drying and oven-drying(P<0.001),but comparable with freeze-dried soil(P>0.2).In conclusion,all drying methods should be considered for use in studies on the land–atmosphere interface and biogeochemical N cycling,whereas the freeze-drying method might be better for studies involving the measurement of soil Nr gas fluxes.
土壤活性氮气体(HONO和NO)排放是全球氮循环的关键过程,对大气化学具有重要意义。本研究采集了农田,草地和森林三种不同土地利用类型的土壤样品,分别对样品进行了风干,冻干和烘干三种处理,并与未处理的新鲜土壤进行比较研究。结果表明,三种类型土壤的冻干土与新鲜土样品的p H值差异最小。总的来说,三种干燥处理都能提高新鲜土壤NH4+-N, NO3--N和溶解态有机N的含量。与新鲜土壤相比,冻干土壤HONO和NO的最大排放通量及完整干湿交替循环的总排放量没有显著增加,而风干和烘干土壤显著增加。因此,冷冻干燥方法可能更适合涉及土壤活性氮气体排放通量的研究。这一发现的重要启示是,我们需要慎重评价以往基于不同干燥方法得到的有关陆地–大气界面活性氮交换过程和生物地球化学氮循环机制的认识。
基金
This work was sponsored by the National Natural Science Foundation of China[grant numbers 41807449,41761144062,and 41730646]
the Shanghai Pujiang Program[grant number 18PJ1403500]
the Fundamental Research Funds for the Central Universities.
