植被冠层氨释放及其对草地氨挥发贡献与源解析

Ammonia release from vegetation canopies and its contribution to grassland ammonia volatilization and source apportionment

为原位监测不同植被的草地土壤与冠层氨挥发,并考察不同植被冠层氨释放的生理机制及其对草地氨挥发的贡献,本研究选择3个品种(麦冬、高羊茅和狗牙根),每个品种设置3个施肥处理(不施氮、30 g·m^(-2)缓释尿素和30 g·m^(-2)尿素)。采用泵吸式便携氨气探测仪原位监测土壤和冠层氨挥发,采用酶联免疫法测定叶片的乙醇酸氧化酶(GO)、甘氨酸脱羧酶(GDC)、谷氨酰胺合成酶(GS)和苯丙氨酸解氨酶(PAL)等酶活性。结果表明:3种草地的土壤、冠层和草地的周年氨挥发量分别为2.8~135.3, 1.6~101.6、4.4~236.9 kg·hm^(-2)·a^(-1)。施用氮肥显著增加了土壤和冠层的氨挥发,狗牙根对氮肥的响应大于麦冬和高羊茅。在测定周期内冠层氨为净释放,冠层氨释放量占草地总氨挥发量的37%~39%;C3和C4植物冠层氨通量均受苯丙氨酸解氨酶和质外体pH的显著正向影响(P<0.05),C4草地还受甘氨酸脱羧酶显著负向调控(P<0.05)。草地土壤氨挥发主要受铵态氮的控制(P<0.05)。研究表明,冠层氨释放是草地氨挥发的重要来源,C3和C4植物冠层氨来源均与苯丙氨酸代谢途径有关,C4植物光呼吸和氮同化途径负向调控冠层氨挥发,C3植物的光呼吸通过苯丙氨酸代谢途径间接影响冠层氨释放。

The main aims of this study were to quantify soil ammonia volatilization(AV)and canopy ammonia emission(AE)of three lawn varieties and to investigate the physiological mechanism of canopy emission and its contribution to turfgrass AV.A randomized block experiment was used,which included three varieties(Ophiopogon japonicus,tall fescue,and bermudagrass)and three fertilization treatments(no nitrogen treatment,30 g·m^(-2) slow-release urea,and 30 g·m^(-2) urea).The soil and canopy ammonia emissions were monitored in situ with a portable ammonia detector between March 2021 and November 2021,and glycolate oxidase(GO)and glycine decarboxylase(GDC),glutamine synthase(GS),and phenylalanine ammonia lyase(PAL)activities in the canopy were measured by enzyme-linked immunosorbent assay.The results were as follows:the accumulated soil AV,canopy AE,and total ammonia loss in the tall fescue,bermudagrass,and O.japonicus were 2.8-135.3,1.6-101.6 kg·hm^(-2)·a^(-1),and 4.4-236.9 kg·hm^(-2)·a^(-1),respectively.The application of nitrogen fertilizer significantly increased soil AV and canopy AE.The response of bermudagrass to nitrogen fertilizer was greater than that of O.japonicus and tall fescue.Canopy ammonia emissions were important sources of turf fields,contributing approximately 37%-39%of the total turf field volatilization.Canopy ammonia fluxes were significantly positively affected by PAL and apoplast pH and significantly negatively regulated by GDC(P<0.05)in C4 plants.Soil AV was mainly controlled by soil ammonium nitrogen(P<0.05).In conclusion,canopy ammonia emissions had pivotal impact on the turf field AV;both C3 and C4 plant canopy ammonia emission sources were phenylalanine metabolic pathways,and it was directly negatively regulated by photorespiration and nitrogen assimilation in C4 plants;however,it was indirectly negatively regulated by photorespiration via the phenylalanine metabolic pathway in C3 plants.