| Litter plays a vital role in the forest ecosystem.It is an important”Iink" connecting forest soil and forest litter,and plays an indispensable role in the process of transforming biological carbon pool into soil carbon pool.Changes in atmospheric nitrogen deposition will affect the production and decomposition of litter,while nitrogen addition will change the global nitrogen cycle,thus affecting the decomposition of forest litter and changes in soil physical and chemical properties.Therefore,studying the effects of nitrogen addition on litter decomposition and soil physicochemical properties is of great scientific significance for a deeper understanding of the impact of global nitrogen deposition on forest ecosystems.This study focuses in the litter of Cunninghamia lanceolate and Phoebe bournei,as well as the surface soil beneath the fallen bags.From July 2021 to July 2022,We conducted the field experiment in the litter of Cunninghamia lanceolate and Phoebe bournei by using the litterbag method,We studied the effects of different nitrogen addition concentrations(N0:0 gN·m-2·a-1;N1:7 gN·m-2·a-1;N2:14 gN·m-2·a-1;N3:28 gN·m-2·a-1;N4:56 g N·m-2a·-1)on the decomposition rate,nutrient content,and soil nutrient content of litter in Cunninghamia lanceolate Phoebe bournei mixed forest.The results indicate that:(1)After one year of decomposition,the mass loss of in the litter of Cunninghamia lanceolate and Phoebe bournei showed a decreasing trend with the increase of nitrogen addition concentration.Nitrogen addition showed a significant inhibitory effect on their decomposition,and the higher the nitrogen application concentration,the stronger the inhibitory effect.The nitrogen addition treatment increased the time for 95%loss of Cunninghamia lanceolate leaf litter quality by 0.83-1.72 years compared to 4.88 years,while the nitrogen addition treatment increased the time for 95%loss of Phoebe bournei leaf litter quality by 0.20-1.45 years compared to 5.08 years.Research has shown that the quality loss and decomposition rate of Phoebe bournei’s fallen leaves are greater than those of Cunninghamia lanceolate.(2)After one year of decomposition,the residual lignin rates of Cunninghamia lanceolate litter treated with nitrogen addition increased by 11.24%,25.97%,29.20%,and 34.53%compared to the control N0,respectively;The lignin residue rates of Phoebe bournei withered leaves treated with nitrogen addition increased by 6.26%,10.76%,20.98%,and 68.91%compared to N0,respectively.The nitrogen addition inhibited the degradation of lignin in the litter of Cunninghamia lanceolate and Phoebe bournei,which is the main reason for the decrease in decomposition rate of Cunninghamia lanceolate and Phoebe bournei leaves caused by nitrogen addition.(3)After one year of decomposition,the potassium and lignin content in the leaves of Cunninghamia lanceolate litter showed an upward trend,while the calcium content showed a downward trend;The carbon content,nitrogen content,phosphorus content,potassium content,magnesium content and lignin content of Phoebe bournei litter leaves showed an upward trend,while the calcium content and hemicellulose content showed a downward trend.The effect of nitrogen addition on the dynamic changes of nutrient content in the litter of Cunninghamia lanceolate and Phoebe bournei varies.There is a correlation between the quality residue rate of in the litter of Cunninghamia lanceolate and Phoebe bournei and the nutrient residue rate of fallen leaves,among which there is a highly significant positive correlation with C residue rate,lignin residue rate,and cellulose residue rate.(4)After one year of nitrogen application,the soil pH values of each nitrogen addition treatment decreased by 0.58%and 0 88%,1.42%,and 3.33%;The total nitrogen content in the soil of each nitrogen addition treatment increased by 14.94%,18.25%,22.80%,and 29.10%compared to the control N0,respectively;The total phosphorus content in the soil of each nitrogen addition treatment increased by 5.5%compared to the control NO 27%,11.97%,8.37%,and 6.18%;The soil N/P of each nitrogen addition treatment increased by 9.9%compared to the control N0 19%,5.63%,13.32%,and 21.59%;The soil C/N of each nitrogen addition treatment decreased by 6.61%,13.81%,22.58%,and 28.63%compared to the control N0,respectively.The nitrogen addition treatment increased the total nitrogen,total phosphorus content,and N/P of the soil,and decreased the soil pH and C/N.(5)The nutrient content in the litter of Cunninghamia lanceolate and Phoebe bournei is significantly correlated with soil nutrients.The nitrogen content in the litter of Cunninghamia lanceolate and Phoebe bournei is highly significantly positively correlated with the total nitrogen content in the soil,while the C/N in the litter of Cunninghamia lanceolate and Phoebe bournei is significantly negatively correlated with the total nitrogen content in the soil.Correlation analysis shows that the analysis results of the litter and soil physicochemical properties of Cunninghamia lanceolate and Phoebe bournei are not completely consistent,possibly due to the difference in initial substrate quality of the two tree species’ litter.In conclusion,nitrogen addition does not affect litter decomposition,nutrie nt release,lignin,cellulose and hemicellulose decomposition and soil physical a nd chemical properties of the mixed forest of Cunninghamia lanceolate and Ph oebe bournei,but is also affected by litter type,nitrogen addition concentration and other factors.Nitrogen addition changed the decomposition law of Cunnin ghamia lanceolate and Phoebe bournei litter,affecting the decomposition rate o f litter.Nitrogen addition inhibited the decomposition of Cunninghamia lanceol ate and Phoebe bournei litter,which may affect the normal cycle of material a nd energy in the mixed forest ecosystem of Cunninghamia lanceolate and Phoe be bournei,and affect the stability of soil carbon pool. |
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