Study On Effects Of Nitrogen And Phosphorus Addition On Organic Carbon Mineralization In Saline-alkali Farmland In Western Jilin Province,China

Soil organic carbon?SOC?is the largest and most active carbon pool in the terrestrial ecosystem of the earth.The global SOC storage is 1200²000 Pg,which exceeds the sum of vegetation and atmospheric organic carbon.Soil organic carbon mineralization is an essential biochemical process closely related to the release of soil nutrients,the maintenance of soil quality and the formation of greenhouse gases.Nitrogen and phosphorus are coupled with carbon-nitrogen cycle by affecting the plant photosynthesis and decomposition of soil organic matter.The utilization of nitrogen and phosphorus is one of the important mechanism of SOC mineralization.The dynamic process of SOC includes two aspects.On the one hand,CO₂ is released through mineralization,and on the other hand,it is stabilized by humus.Adding nitrogen and phosphorus can promote the SOC mineralization,mainly through the following 3aspects:?1?Nitrogen and phosphorus are important nutrient limiting factors for plant growth in the ecosystem.Nitrogen and phosphorus additions improve soil fertility,plant primary productivity and promote SOC mineralization.?2?The addition of nitrogen and phosphorus promotes the activities of microorganisms and soil enzymes,thereby promoting the SOC mineralization.?3?The addition of nitrogen and phosphorus makes the pH of saline-alkali soil drop,improves plant root activity,and promotes SOC mineralization.It studies the influences of different forms of nitrogen and phosphorus addition on the SOC mineralization and priming effect.The west of Jilin is the important commercial grain base in China and one of the three salt and alkali soil distribution areas in the world.“Research on transfer flux and mechanism of soil organic-inorganic carbon in saline-alkali soil in the west of Jilin”is an NFSC project chaired by my tutor.Based on this project,we select three saline-alkali upland soil samples?H1,H2,H3?and three saline-alkali paddy soil samples?S1,S2,S3?,add 7 forms of inorganic nutrients??NH₄?₂SO₄?,KNO₃ and KH₂PO₄)to 0¹5 cm surface soil,monitor the carbon dioxide emission in the 25?incubator for 32 days and record their values in the 1st,2nd,4th,9th,18th and 32th day.It analyzes the influences of 7 different treatments on the mineralization and priming effect in three stages,including early stage?0⁴ day?,middle stage?5¹7 day?and late stage?18³2 day?.In general,the research on SOC mineralization of nitrogen and phosphorus is mainly concentrated in forests,swamps and other places,and less research on saline-alkali farmland.In forest soils with high organic carbon content,the addition of nitrogen and phosphorus may reduce the SOC mineralization and allow SOC to be stored.However,we found that in the case of high salinity and low SOC content,the addition of nitrogen and phosphorus can stimulate SOC mineralization easily and produce a positive priming effect.The results show that after adding nitrogen and phosphorus,the amount of organic carbon mineralization was increased with the prolongation of incubation time.In the early stage?0⁴ day?,the amount of SOC mineralization had no obvious difference among different soils,but the accumulation of mineralization had increased to 158.5%⁹76.5%in the late stage?18³2 day?.The higher the concentration of the same additive was,the more the accumulation of SOC mineralization was.Obviously,the addition of nitrogen and phosphorus improve the rate of SOC mineralization to 158.5%⁷70.5%.There is the similar varying trend between the mineralization rate of upland soil and paddy soil,from rapid decline in the early stage?0⁴ day?to slow decline in the middle stage?5¹7 day?,and then to tend to be gentle and positive in the late stage?18³2 day?.There were positive priming effects among the different groups of upland soil and paddy soil,but they had no obvious regularity.It indicates that the addition of nitrogen and phosphorus can promote the function of mineralization for several days.Compared to paddy soil,the mineralization and stimulation of SOC in upland soil was generally more responsive to the addition of nitrogen and phosphorus.Different soil textures,temperature conditions,water conditions,additives and other factors will affect the SOC mineralization.These factors not only independently affect the decomposition of SOC,but also have an interactive relationship with each other.They also work together to affect the SOC mineralization.By correlation analysis,total carbon content?TC?and total organic carbon content?TOC?were positively correlated?p<0.01?,Na⁺and electroconductibility?EC?were positively correlated?p<0.01?,pH,Na⁺and exchangeable sodium percentage?ESP?were positively correlated?p<0.01?,pH and TOC were negatively correlated?p<0.01?.During the incubation,the SOC mineralization and priming effect showed a significant correlation with the basic properties.The SOC mineralization and priming effect showed negative correlation with alkalization and positive correlation with carbon and nitrogen content.