【作者】 王刚；

【导师】 沈禹颖；

【作者基本信息】 兰州大学 ， 草学， 2018， 硕士

【摘要】 随着全球气候变暖加剧,温室气体减排备受关注。N₂O被认为是造成全球温室效应的三大气体之一。目前,国内有关N₂O排放特征的研究主要集中于南方稻田以及北方主要粮食作物种植区。紫花苜蓿作为牧草之王,具有培肥地力、减少氮肥投入以及改善土壤质量等作用。然而,关于旱作苜蓿草地N₂O排放特征的研究相对较少,对N₂O排放日动态、季节特征以及影响因素等尚不明确。研究以兰州大学庆阳黄土高原试验站为依托,开展了陇东旱塬苜蓿草地N₂O排放特征及其对氮肥施用和硝化抑制剂添加的响应的研究。本研究共设置5个处理。其中,氮肥施用量设4个水平,分别为N0（CK）、N50(50 kg N hm^-2)、N100(100 kg N hm^-2)和N150(150 kg N hm^-2)。此外,在N150处理的基础上添加硝化抑制剂-双氰胺（DCD）,即N150+DCD处理。采用LGR-N₂O/CO气体分析仪和传统静态箱法相结合的方法监测不同处理苜蓿草地N₂O排放动态及特征。同时,动态监测土壤温度、湿度、硝态氮含量以及苜蓿产量等因素,用以探究苜蓿草地N₂O排放的影响因素,以期获得陇东旱塬苜蓿草地N₂O的排放特征及其对施氮和添加硝化抑制剂的响应机制。研究成果对于准确评估黄土高原旱作苜蓿草地N₂O排放强度及特征提供数据支撑,同时可定量硝化抑制剂对苜蓿草地N₂O的减排效果。研究获得的主要结果如下:1.于2014年7⁸月份,采用LGR-N₂O/CO气体分析仪监测不同施氮梯度下(0 kg N hm^-2和150 kg N hm^-2)陇东苜蓿草地N₂O排放的日动态和平均排放通量。研究表明,N₂O排放通量具有明显的日变化特征,表现为先降低后增加的趋势。通过日排放特征发现,以9:00¹1:00时测定的N₂O通量值为基础推算日尺度或更长时间尺度的N₂O排放通量时可能存在明显低估的现象。监测期内,N0和N150处理N₂O排放通量的变幅分别为-0.0368⁰.0665 mg m^-22 h^-1和-0.0093⁰.0466 mg m^-2 h^-1,平均值分别为-0.0036和0.0118 mg m^-2 h^-1,N150处理的排放量较N0处理明显增加。不同施氮处理下N₂O排放量均随土壤含水量的增加而增加。2.于2017年5⁹月份,采用传统静态箱法测定了不同氮肥梯度下(0、50、100和150 kg N hm^-2)陇东苜蓿草地N₂O排放特征。结果显示,监测期内N₂O排放通量的变幅为-0.0021⁰.0510 mg m^-2 h^-1。其中,N0、N50、N100和N150处理N₂O平均排通放量分别为0.0035、0.0041、0.0050和0.0061 mg m^-2 h^-1。监测期内各处理N₂O累计排放量分别为6.5、8.0、9.2和11.2 mg m^-2。N50、N100和N150处理N₂O排放系数分别为0.030%、0.027%和0.031%。N₂O排放量随着氮肥梯度的增加而增加。施氮处理对苜蓿的产量没有显著影响（P>0.05）。N0、N50、N100和N150处理单位苜蓿产量N₂O排放量分别为6.5、7.8、11.3和12.5 mg kg^-1。3.于2017年5⁹月份,采用传统静态箱法测定了施氮处理(0、150 kg N ha^-1)及配施硝化抑制剂N150+DCD(DCD+150 kg N ha^-1)处理下陇东苜蓿草地N₂O排放特征。结果显示,生长季内N0、N150和N150+DCD处理N₂O平均排放通量分别为0.0035、0.0061和0.0026 mg m^-2 h^-1,累计排放量分别为6.5、11.2和4.3 mg m^-2,随着氮肥梯度的增加N₂O排放量而增加。N150和N150+DCD处理N₂O的排放系数分别为0.03%和-0.01%。N150+DCD处理对N₂O排放具有显著的抑制作用。与N150处理相比,N150+DCD处理N₂O的排放量降低62%,抑制剂显著降低了N₂O排放。N₂O排放通量与土壤水分存在显著相关性（P<0.05）,N₂O排放通量随土壤水分的增加而增加。N0、N150和N150+DCD处理单位苜蓿产量N₂O排放量分别为6.5、12.5和6.0 mg kg^-1。本研究通过开展陇东旱塬苜蓿草地N₂O排放特征及其对氮添加和配施硝化抑制剂双氰胺的响应机制研究,阐明了氮添加下陇东旱塬苜蓿草地N₂O排放特征以及土壤温湿度、土壤硝态氮含量的变化,发现苜蓿草地N₂O排放量随着氮梯度和土壤含水量的增加而增加。硝化抑制剂双氰胺对N₂O的排放具有显著的抑制作用。更多还原

【Abstract】 Global warming has accented the importance in mitigating greenhouse gas（GHG）emission.N₂O is considered to be one of potent GHG that contribute to the global warming largly.A large number of studies have shown that agricultural soil is an important source of N₂O emissions,as it accounts for 50%of global N₂O emissions.N₂O produced by soil can account for 70%to 90%of the total N₂O released from the biosphere to the atmosphere.At present,research on N₂O emission characteristics in China is mainly focused on paddy fields in the south and the main grian crop growing areas in the north.As the king of forage crop,alfalfa has good feeding value,and the functions of reducing nitrogen fertilizer input and improving soil quality.Therefore,it is widely planted in the Loess Plateau of East Gansu Province,which promotes local social,economic and ecological benefits.However,there are relatively few studies on the N₂O emission characteristics of alfalfa grasslands in the region,and the daily dynamics,seasonal characteristics,and influencing factors of N₂O emissions are not yet clear.The use of nitrification inhibitors in combination with nitrogenous fertilizers,by controlling the activity of nitrifying bacteria,enables the nitrogen source applied to the soil to exist in the form of ammonium nitrogen for longer periods for the crops to absorb and use,which not only increases the nitrogen fertilizer in the soil,but also reduces nitrogen leaching,and N₂O emissions from the soil.Therefore,the effects of nitrification inhibitors on N₂O emissions from alfalfa grassland need to be further explored.In view of this,based on the Qingyang loess plateau experimental station of Lanzhou University,we carried out the N₂O emission characteristics of dryland grassland in eastern Gansu and its response to nitrogen fertilizer application and nitrification inhibitor addition.A total of 5 treatments were set up in this study.Among them,nitrogen fertilizer application levels were set at 4 levels,namely N0（CK）,N50(50 kg N hm^-2),N100(100 kg N hm^-2),and N150(150 kg N hm^-2).In addition,a nitrification inhibitor,dicyandiamide（DCD）,N150+DCD,was added to the N150 treatment.Using a combination of LGR-N₂O/CO gas analyzer and traditional static chamber-gas chromatography to monitor the dynamics and characteristics of N₂O emissions from different treatments of alfalfa grassland.At the same time,dynamic monitoring of soil temperature,moisture,NO₃^-content and alfalfa production and other factors,in order to explore the influencing factors of N₂O emissions from alfalfa grassland,in order to obtain the characteristics of N₂O emissions and its application of nitrogen and nitrification inhibitor response mechanism.The results provided data support for accurate assessment of N₂O emission intensity and characteristics of dry-crop lands on the Loess Plateau,and can also quantify the effect of nitrification inhibitors on N₂O reduction of alfalfa grassland.The main results obtained from the study are as follows:1.In July and August of 2014,the daily dynamics and average N₂O emissions from the alfalfa stands under different nitrogen application rate(0 kg N hm^-22 and 150 kg N hm^-2)were monitored using the LGR-N₂O/CO gas analyzer.The results showed that N₂O fluxes had a distinct diurnal variation characteristic,showing a trend of decreasing first and then increasing.According to the daily emission characteristics,the N₂O fluxes at the daily or longer time scales may be underestimated when the N₂O flux values measured from 9:00 to 11:00.During the monitoring period,the amplitudes of N₂O emission fluxes of N0 and N150 were-0.0368-0.0665 mg m^-2 h^-1and-0.0093-0.0466 mg m^-2 h^-1.The average values were-0.0036.And 0.0118 mg m^-2 h^-1,N150treatment significantly increased N₂O emissions,compared with N0 treatment.The N₂O emissions under different nitrogen treatments increased with the increase of soil water content.2.From May to September of 2017,the N₂O emission characteristics of the alfalfa grassland at different nitrogen fertilizer gradients(0,50,100,and 150 kg N hm^-2)were measured using a conventional static chamber-gas chromatography method.The results showed that the amplitude of N₂O emission during the monitoring period ranged from-0.0021 to 0.0510 mg m^-2 h^-1.Among them,the N0,N50,N100 and N150 treatment N₂O average discharge capacity were 0.0035,0.0041,0.0050 and 0.0061 mg m^-2 h^-1,respectively.During the monitoring period,the cumulative N₂O emission from above treatments was 6.5,8.0,9.2,and 11.2 mg m^-2,respectively.The N₂O emission coefficients of N50,N100,and N150 treatments were 0.030,0.027,and 0.031,respectively.The N₂O emissions per unit of production of N0,N50,N100,and N150 were 6.5,7.8,11.3,and 12.5 mg kg^-1,respectivel.3.From May to September of 2017,the traditional static chamber method was used to determine the N₂O emission characteristics under nitrogen application at 0,150 kg N hm^-2 and the application of nitrification inhibitor DCD together with 150 kg N hm^-2.The results showed that the average N₂O emission fluxes under N0,N150,and N150+DCD during the growing season were 0.0035,0.0061,and 0.0026 mg m^-2 h^-1.The cumulative emissions were 6.5,11.2,and 4.3 mg m^-2,respectively.With the increase of nitrogen fertilizer gradient,N₂O emissions increased.Emission factors for N150 and N150+DCD treatments were 0.03 and-0.01 respectively.N150+DCD treatment had a significant emission reduction effect on N₂O emissions.Compared with N150 treatment,N150+DCD treatment reduced N₂O emissions by 62%,and inhibitors significantly reduced N₂O emissions.N₂O flux was significantly correlated with soil moisture（P<0.05）,and N₂O flux increased with increasing soil moisture.The N₂O emissions of N0,N150and N150+DCD treatment units were 6.5,12.5 and 6.0 mg kg^-1,respectively.In this study,we studied the N₂O emission characteristics of alfafa grassland and its response mechanism to nitrogen addition and application of nitrification inhibitor dicyandiamide.Changes in nitrate nitrogen content and aboveground plant yield revealed that N₂O emissions from alfalfa grassland increased with the increasing of nitrogen allicationa rate and soil moisture content.Nitrification inhibitor had a significant inhibitory effect on N₂O emission.更多还原