Effect Of Fertilization On Priming Effect Of Soil Organic Carbon And Net Carbon Balance In Alpine Meadows

Input of labile organic carbon can change decomposition process of soil organic carbon(SOC)through priming effect.The atmospheric deposition of nitrogen(N)and phosphorus(P)caused by human activities impacted the structure and function of grassland ecosystem.However,there is no consistent conclusion on the response and mechanism of SOC decomposition and accumulation to N and P input in grassland ecosystems.In this paper,we studied the effects of long-term N and P fertilizer addition(CK: no fertilization,N: nitrogen fertilizer,P: phosphate fertilizer,and NP: combined nitrogen and phosphorus fertilizer)on SOC priming and net C balance in alpine meadow of the Tibetan plateau.We carried out the study through field experiment combined with incubation experiment and using labeled glucose and vanillin represented exogenous carbon of different quality.We expect to reveal the mechanism of the effect of N and P input on soil organic carbon decomposition and sequestration.The results showed that:1.The priming effect of P treatment was significantly higher than that of CK in different doses of glucose addition,and the increment of the priming effect of P was the largest(3 times of CK)in medium dose addition.The priming effect of N and NP treatment was significantly lower than that of CK at low and high dose of glucose input,but they were higher than priming effect of CK in medium dose addition.The priming effect of P treatment was increased by 5 and 18 times than that of CK after the addition of vanillin and glucose.2.The amount of glucose decomposed in P,NP treatment was significantly lower than that of CK at different doses of exogenous C input,and that of P treatment was the lowest among the three added doses.The amount of glucose decomposed in N treatment was significantly higher than that of CK treatment at low dose addition.The substrate decomposed in P,NP treatment with vanillin addition was significantly lower than that of CK,N treatment with added glucose was 45.5 % higher than CK.3.At low and high doses of exogenous C input,the net C balance of N,NP was significantly higher than that of CK.However,there was no significant difference in net C balance between different fertilization treatments at medium dose addition.The net C balance of P treatment was significantly lower than that of other fertilization treatments in vanillin and glucose addition.The net C balance of NP treatment was significantly higher than that of CK in vanillin addition.4.SOC decomposition of N,P and NP treatment were significantly lower than CK in no glucose addition.The cumulative decomposed SOC of N,NP treatment was significantly lower than that of CK in different doses of glucose addition.At low glucose addition,the cumulative decomposed SOC of P treatment was 8.4% lower than that of CK.At medium and high doses addition,the cumulative decomposed SOC of P treatment was 14.3% and 8.3% higher than that of CK,respectively.The accumulated decomposed SOC of P treatment is significantly higher than that of CK in vanillin and glucose addition.5.The priming effect was correlated with soil physical,chemical properties and microorganisms(positively correlated with MBC: MBN,WC,TP and pH,and negatively correlated with SOC,MBN,BGB,TN,C:N,BD and AN).From the above results,the following conclusions can be drawn:1.The quantity and quality of exogenous carbon input which was changed by fertilization caused positive priming effect,but the decomposition amount of SOC of applying nitrogen fertilizer was significantly lower than that of CK,and microorganisms made more use of exogenous carbon and slowed down the decomposition of SOC.2.The priming effect of P treatment was higher than other treatments,especially the influence of exogenous carbon structure on the excitation effect is greater than that of carbon quantity.The mineralization amount of SOC of P treatment was significantly higher than that of CK,which promoted the decomposition of soil carbon.