硅胶管气样原位采集技术研究土壤N_2O浓度及通量变化

箱法被广泛用于监测土壤N_2O排放通量,但在原位采集高浓度土壤N_2O、全天候监测N_2O通量变化、动态研究土壤剖面N_2O的行为等方面存在弊端.本研究通过室内模拟硅胶管对N_2O的通透性,探索硅胶管用于原位采集土壤气样的理论可行性.田间试验设施用铵态氮肥(NH_4~+)、施用硝态氮肥(NO_3~-)及施用硝态氮肥加葡萄糖(NO_3~-+C)等3个处理,同时安置硅胶管和采样箱,验证硅胶管法在原位采集高浓度土壤N_2O气样、监测土壤N_2O浓度以及排放通量的实际效果,并与箱法进行比较.结果表明,硅胶管内外的N_2O气体经2.9 h达到95%的平衡,完伞能满足大田采样要求;用硅胶管法原位采集高浓度土壤N_2O气样的效果显著优于箱法采样.其浓度变化表现出明显的时间规律,浓度梯度法计算的N_2O排放通量与箱法测定结果呈显著正相关,但数值偏低;偏低的程度取决于采样位置和土壤中N_2O产生位置的匹配程度.建议采用埋于土壤表层的硅胶管计算地面N_2O排放通量,或在不同土层埋人硅胶管研究土壤剖面N_2O行为的时空变异.

Use of silicone tubes as a simple method to measure in situ soil gas N_2O concentrations and fluxes

Chamber method,which was used as a regular way to measure N_2O fluxes from soils,has the disadvantages on sampling in situ soil-derived N_2O with high concentration,monitoring N_2O fluxes under all weather conditions and studying the behaviors of N_2O in soil profile.The possibility of using silicone tubes to sample in situ soil gas Was tested by measuring the diffusivity of standard N_2O gas through the silicone tube walls.Field plots were under treatments of NH_4~+、NO_3~- and NO_3~- plus glucose,with four randomly arranged replicates.Silicone tubes and sampling chambers were buried under soil surface with different depths.In situ collection of soil N_2O with hish concentration and the efficiency of monitoting the concentration and fluxes of N_2O were compared,as the silicone tube and traditional chamber had different sensitivity to N_2O variation in soil.Results revealed that it took only 2.9 hours for N_2O in the silicone inner space to reach95% equilibrium with the surrounding atmosphere,which was fast enough to satisfy regular sampling interval.The silicone tubes method had the advantage over chamber method in collection of soil-derived N_2O with high concentration and the collected sample showed clear trends concerning N_2O concentration over time.The temporal variation of N_2O emissions calculated by different methods showed significantly positive correlations,while the silicone tube method gave lowervalues.The agreement of two data sets depended on the matching of the site of sampling and N_2O production.It is recommended to bury horizontal silicone tube at surface soil layer for N_2O flux monitoring or at different soil depths to investigate the spatial and temporal variation of N_2O behavior in soil profile.