Simulate The Effects Of Root Exudates On Soil N₂O Emission

N₂O is an important greenhouse gas which can destroy ozone layer in stratosphere and participate in certain photochemical reactions in atmosphere,aggravating greenhouse effect.N₂O emitted by soil accounts for about 65%of total N₂O emissions in the world.The vegetable fields have the characteristics of high soil moisture and high fertilizer,which is conducive to the production of N₂O.Root exudates is one of the important carbon source for soil,affecting microbial activity and nutrient morphology around rhizosphere.Oxalic acid,serine and glucose are representative compounds in the root exudates.In this paper,Indoor cultivation experiments was carried out with addition of oxalic acid,serine,and glucose in soil.The effects of these representative root exudates on soil N₂O emissions and microbial production pathways were studied using stable isotope techniques,with a view to providing theoretical support and basic data for reduction N₂O emission in vegetable fields and environmental pollution control.Main contents of the paper are as follow:Study on the effects of different root exudates on N₂O emissions of soil in a day.Indoor cultivation experiments were carried out for 4 days with two levels of concentration of oxalic acid,serine and glucose treatment and distilled water added.The N₂O emission rate,daily cumulative emission and isotope signatures(?¹⁵N^bulk,?¹⁸O and SP(intramolecular ¹⁵N site preference,?¹⁵N^?-?¹⁵N^?))of N₂O at different incubation time were measured on 4th day.Analysis results are as follow:?1?After adding 3 kinds of root exudate components,the N₂O emission rate of soil increased gradually,which was higher than that of the control.?2?The values of N₂O-?¹⁸O were not different among different root exudate treatments,but root exudates treatment group significantly higher than the control;The value of N₂O-?¹⁵N^bulk was related to the component of root exudates added.?3?After a comprehensive analysis of the correction coefficients of four indexes(N₂O emission rate,the value of?¹⁵N^bulk,?¹⁸O and SP)the best sampling time is 16th hour after the addition of root exudates.Study on the effects of different root exudates on N₂O emissions from soil roots in short-term?32days?.Indoor cultivation experiments were carried out for 32 days with two levels of concentration of oxalic acid,serine and glucose treatment and distilled water added under air,anaerobic,anaerobic+acetylene condition.At the same time distilled water treatment was set for control.N₂O emission rate,cumulative emissions of N₂O and its isotope values(?¹⁵N^bulk??¹⁸O and SP(site preference,SP=?¹⁵N^?-?¹⁵N^?))of every gas sample detected.The concentration of NH₄⁺and NO₃^-in soil isotopes of NO₃^-(?¹⁵N and?¹⁸O)were tested.The results are as follow:?1?During the first 11 days of cultivation,After adding root exudates,the soil N₂O emission rate increased first and then decreased rapidly maintaining a certain emission potential;?2?During the 11-30 days of cultivation,the N₂O emission rate of the root exudate treatment was low,and the distilled water treatment continued to increase;after the N source was added again,N₂O was quickly discharged.The emission rate of N₂O emission rate of different treatments is higher than that of the control,and the peak period of N₂O emission of each treatment is also different.?3?The higher the concentration of the treatment of the root exudates,the faster the transformation rate of NH₄⁺to NO₃^-.?4?According to N₂O-?¹⁵N^bulk?N₂O-?¹⁸O and the map of SP-?¹⁸O and SP-?¹⁵N^bulk,N₂O emission mainly from bacterial denitrification and nitrifier denitrification process during the first 11 days and N₂O reduction was observed from both root exudates treatment and control.The contribution of nitrification to N₂O emission of distilled water is high.In summary,the results of this paper show that:adding root exudates can increase the contribution of soil N₂O denitrification production pathways;The contribution of different types of root exudates to denitrification is different.The research results have important reference value and guiding significance for China to formulate reasonable measures to promote the reduction of farmland soil greenhouse gas N₂O emissions.