Characteristics Of Nitrous Oxide And Nitric Oxide Background Emissions From A Tea Plantation

Nitrous oxide(N2O)and nitric oxide(NO)are two of the most important anthropogenic nitrogen compounds emitted to the atmosphere,which are directly or indirectly involved in global warming and atmospheric chemistry,as well as an important part of nitrogen biogeochemical cycle.It has been reported that the soil acidification could not only affect the habitat of tea trees,the quality and yield of tea,but also result in a large number of N2O and NO emissions.China is the largest tea plantation country in the world,and tea is one of the main economic crops.In fact,the soil acidification is increasingly serious in China,there was more than 50%of the tea soil pH less than 4.5 in Chinese typical tea plantation.So far,however,no study is available for N2O and NO fluxes from tea plantation soil between rows and soil under canopy,which hinders the development of a sound N2O and NO emission inventory.To characterize and quantify annual N2O and NO fluxes and to clarify the underlying mechanisms,as well as to assess the contribution of N2O and NO emissions from soil between rows and soil under canopy of tea plants to the total N2O and NO emissions from tea fields and to determine the factors responsible for changes in N2O and NO emissions,we performed in situ measurements of N2O and NO for a 380 days from a Chinese subtropical tea plantation under different soils(i.e.,soil between rows,soil under canopy),using a closed Chamber-Gas Chromatography method.Through this study,the results were as follows:1.N2O fluxes from soil between rows and soil under canopy showed a seasonal variation,with the highest in spring and summer,accounting for approximately 70%of annual cumulative N2O emissions from the soil between rows and soil under canopy;2.Across the annual tea plantation,soil N2O flux ranged from 11.40-408.65?g m-2 h-1 under two types of tea soils.And the cumulative N2O emissions were about 8.459?3.026kg N ha-1 for the soil between rows and soil under canopy,respectively.Meanwhile,total N2O emissions were approximately 65%and 35%of total N2O emissions from the entire tea field in soil between rows and soil under canopy,respectively.So the soil between rows is the main emission source of N2O flux in tea plantation;3.In the soil between rows and soil under canopy,there was a significant correlation between N2O flux and soil temperature,moisture and pH;however,there was a significant negative correlation between N2O flux and ammonium and nitrate content;4.NO fluxes from soil under canopy showed a seasonal variation,with the highest in spring and summer,accounting for approximately 74%of annual cumulative NO emissions from the soil soil under canopy;and there was no significant seasonal variation about NO fluxes from soil between rows;5.Across the annual tea plantation,soil NO flux ranged from-10.73-377.83?g m-2 h-1 under two types of tea soils.And the cumulative NO emissions were about 0.92.2.137kg N ha-1 kg N ha-1 for the soil under canopy and soil between rows,respectively.Meanwhile,total NO emissions were approximately 22%and 78%of total NO emissions from the entire tea field in soil between rows and soil under canopy,respectively.So the soil under canopy is the main emission source of NO flux in tea plantation;6.There was a positive correlation between NO flux and soil temperature,a negative correlation between NO flux and moisture in the soil between rows;there was a significant negative correlation between NO flux and moisture and pH in the soil under canopy;Meanwhile,no matter from soil between rows and soil under canopy,there were no significant correlation between NO flux and ammonium,nitrate content throughout the overall experiment.During the tea-growing period from March to September(i.e.,in the spring and summer seasons),however,in the soil between rows and in the soil under canopy,there was a significant positive correlation between NO flux and ammonium content and a significant negative correlation between NO flux and nitrate content.