Responses Of Boreal Forest Soil Excitation Effects To Nitrogen Addition

Adding exogenous organic carbon(C)to the soil can affect the mineralization of soil organic carbon(SOC),leading to the priming effect(PE).Previous studies have found that nitrogen(N)can affect the mineralization and PE of SOC.However,the mineralization of SOC and how the PE responds to exogenous organic C under different amounts of N addition.Therefore,we selected the boreal forest soils that have been simulated N addition experiments for eight years as the experimental objects,and set 4N addition treatments,namely control(CK)and low N(LN),medium nitrogen(MN)and high nitrogen(HN).Soil sampling was carried out in July 2019 to carry out the determination of soil physical and chemical properties and the addition of different concentrations of ¹³C-labeled glucose laboratory culture.The experimental results showed that long-term N addition can change the physical and chemical properties of soil.In addition,the response of soil microbial biomass carbon(MBC)and nitrogen(MBN)to N addition was very obvious.we found that the addition of glucose can increase the content of MBC and MBN correspondingly.As the amount of N increased,the accumulated mineralization of SOC gradually decreased.Under different N treatments,the SOC mineralization of LN treatment was 11.5%lower than that of CK treatment;the SOC mineralization of MN treatment was 44.6%lower than that of CK treatment;and the SOC mineralization of HN treatment was 59.1%lower than that of CK treatment.Although N addition could inhibit the mineralization of SOC,but regardless of the level of N addition,the addition of glucose would accelerate the mineralization of SOC,thereby producing a positive PE.The cumulative PE values of GL0,GL1,GL2,and GL3 were 5-12,14-18,21-24,and 29-34 mg C g^-1SOC,respectively.In addition,after short-term laboratory training,it was found that the positive PE of the soil made the residual C significantly higher than the loss of SOC,resulting in an increase in the net C content of the soil.The average soil net C changes under the four treatments of GL0,GL1,GL2,and GL3 were 11.25±0.65,16.61±1.05,19.64±1.03,and 23.40±2.34 mg C g^-1 SOC,respectively.In summary,we concluded:1.After the addition of N,the pH value of the soil decreases and the soil microbial biomass also were decreased.These changed inhibit the mineralization and excitation of SOC;however,with the increase of glucose addition,we observed that the mineralization of organic C.The ability was enhanced,and the intensity of the PE increased.2.After adding different amounts of glucose to the soil with long-term N application,the net C balance under each treatment was positive.This indicates that the addition of glucose leads to an increase in the net C content in the soil,which was conducive to the increase in soil C storage.