The Mechanism Of Sorghum Secreted Biological Nitrification Inhibitor MHPP And Its Effect On Soil N₂O Emission

The application of nitrogen fertilizer is one of the important factors in agricultural system,which strongly affects the global nitrogen cycle.The nitrogen fertilization can effectively promote the crop yield,but meanwhile,it also has influence on the ecological environment.Nitrification is an important cause of the loss of nitrogen in the soil.The ammonium nitrogen in soil can be easily transformed to nitrate nitrogen by ammonium oxidation bacteria,among which a small parts of nitrate can be absorbed by plants.The most of nitrate could be leached and transformed into nitrate oxide by following denitrification,which cause the loss of soil nitrogen and low nitrogen use efficiency.The leaching of nitrate caused eutrophication and the nitrate oxide caused atmospheric pollution and greenhouse gas emission.Nitrification inhibitors are specific inhibition of soil ammonia oxidizing bacteria,which are widely used in some developed countries,but its application in our country is not popularized.At present,sorghum has the ability to secrete nitrification inhibitor,p-hydroxybenzene propanoic acid?MHPP?.Therefore,the sorghum hydroponic experiments were conducted to study the mechanism of biological nitrification inhibitor of sorghum secretion.The effect of different nitrogen forms on secretion of biological nitrification inhibitors MHPP in relation with plasma membrane proton pump was investigated.The field experiment,pot experiment and soil cultivation experiments were conducted to analyze the effect of biological nitrification inhibitor application in soil.The effects of biological nitrification inhibitors on crop yields,nitrogen use efficiency,soil ammonium and nitrate concentration,soil pH value and greenhouse gas N₂O emissions were tested.The main results are:1.After sorghums cultured under different nitrogen sources,large amounts of biological nitrification inhibitors MHPP were secreted from sorghum root under ammoniumnutrition.However,no MHPP secreted under nitrate nutrition.The rate of MHPP secretion increased with the concentration of ammonium in the root medium.2.By using fusicoccin whice could activate the activity of proton pump and inhibitor vanadate.It was found that fusicoccin can improve the MHPP release while vanadate reduced MHPP release.4.In the field experiment,the concentration ammonium and nitrate nitrogen in the soil cultivated by sorghum plants were 33mg/kg,98mg/kg,respectively.And the concentration of ammonium and nitrate nitrogen in control soil cultivated by maize were 28 mg/kg,119 mg/kg.In pot experiment,the ammonium and nitrate concentration in sorghum rhizosphere were 17 mg/kg,208 mg/kg,respectively.And the ammonium and nitrate concentration in maize rhizosphere were 13 mg/kg,240 mg/kg,respectively.In laboratory soil incubation experiment,compared with sorghum root exudation treatment,the soil ammonium concentration of control treatment decreased rapidly,and corresponding,the concentration of nitrate increased faster.5.Biological nitrification inhibitors can inhibit soil N₂O emissions in a certain extent.Irn field test,the peak of N₂O emission in control treatmeat is 244 ?gN m-2 h-1,and the peak of N20 emissions in sorghum treatmeat is 148 ?gN m-2 h-1.in pot experiment,no obvious peak of N₂O emission,but the emission of N20 from maize treatment significantly higher than sorghum treatment.In laboratory soil incubation experiment,the peak of N₂O emission in control is 20 ?gN m-2 h-1,and sorghum root exudation treatment is 18 ?gN m-2 h-1.Our results indicated that sorghum could relese MHPP,a nitrification inhibitor,under ammonium N source,which is regulated by plasma membrane H+-ATPase.These biological nitrification inhibitors could strongly inhibit the soil nitrification and following denitrification process,therefore reduce the emission of N₂O.