茶园生态系统的一氧化氮年排放特征

采用静态暗箱-化学发光法,对亚热带典型茶园不同施肥处理(常规施尿素、施有机肥和不施肥对照)条件下的一氧化氮(NO)排放通量进行了原位周年观测。结果显示:施肥茶园的NO排放量主要集中在3—9月(春夏季)的茶树生长期,占全年排放量的58%~73%;土壤铵态氮含量是茶园在春夏季NO排放通量变化的主要环境控制因素;对照、尿素、有机肥处理的NO年排放量分别为2.85、19.42、17.04 kg N·hm^-2,施肥显然大幅度增加了NO排放;与茶农常规施尿素处理相比,施有机肥处理显著降低了约12%的NO年排放量;在整个观测期内,常规施尿素和施有机肥处理的NO年直接排放系数分别为3.68%和3.15%。这些结果表明,我国亚热带茶园可能是一个不容忽视的NO强排放源,对此尚需多地点多年的长期研究进一步证实。

Annual Fluxes of Nitric Oxide from a Tea Plantation Ecosystem

To quantify annual nitric oxide(NO) fluxes and to explore the underlying mechanisms and factors controlling NO fluxes from tea fields, we performed in situ measurements of NO fluxes for a full year in a subtropical tea field with different fertilization managements(i.e., conventional farmers' practice with urea application, alternative practice with organic fertilizer application, and no nitrogen application as a control). Static opaque chamber and chemiluminescent analysis were used. Results demonstrated that the majority of NO fluxes occurred during tea tree-growing period from March to September(i.e., in the spring and summer seasons), accounting for approximately 58%~73% of annual cumulative NO fluxes from the fertilized tea fields. During this period, soil ammonium content was the key environmental factor regulating the temporal variations of NO fluxes. The cumulative NO fluxes were about 2.85, 19.42 and 17.04 kg N·hm^-2 for the control, urea and organic fertilizer treatments, respectively, with fertilization significantly increasing NO fluxes. Of the fertilized treatments, applying organic fertilizer significantly reduced annual NO emissions by 12%, as compared to urea application. The direct emission factor of NO for urea and organic fertilizer amendments was estimated to be 3.68% and 3.15%, respectively, highlighting high NO emissions from tea plantations.