Effects Of Elevation Gradient And Litter Manipulation On Soil Respiration And Its Temperature Sensitivity In Pinus Taiwanensis Forest

Understory soil respiration is the most considerable carbon output process of the forest ecosystem,and its small changes will have a significant impact on the forest carbon budget.However,there are still uncertainties in how different forest soil respiration(R_S)components(Heterotrophic respiration R_H,Autotrophic respiration R_A)and their temperature sensitivity(Q₁₀)respond to changes in altitude and litter input.To explore the patterns of R_Sand Q₁₀controlling by elevations and litter,this study set up sample plots S1-S5(1200m,1400m,1600m,1800m,2000m,respectively)for Pinus taiwanensis forest in Wuyi Mountain,and test the soil respiration characteristics.We conducted experimental observations for about two years.It is proposed to study soil respiration components'characteristics at different elevations from the perspectives of climate,soil properties,vegetation and litter characteristics of Pinus taiwanensis,microbial community to solve the three scientific questions.1)How do elevation and the characteristics of the Pinus taiwanensis community affect the respiration rate,annual flux ratio,and Q₁₀of different soil respiration components?What is the mainly factors?2)How does the manipulation of litter affect the characteristics of soil respiration in Pinus taiwanensis forest at different elevations?How does its network relationship of litter quality predict these changes?3)How the treatment of litter manipulate and the root removal in Pinus taiwanensis forests coordinate with the microbial changes to regulate soil respiration?The following conclusions are listed as below.(1)Repeated-measure analysis of variance showed the total respiration rate(R_S)and heterotrophic respiration rate(R_H)have significant differences among the elevations.The ratios of autotrophic respiration to total soil respiration(E_RA:E_RS)of Pinus taiwanensis showed increased first and then decreased with the decrease of elevations,which is opposite to ratios of heterotrophic respiration and total soil respiration(E_RH:E_RS)changes.The temperature sensitivity(Q₁₀)of different respiration components are showing the highest at S1 and S5.The soil dissolved organic carbon and nitrogen,and p H together can explain 72.72%of the variation in E_RS,E_RH,and E_RAat different elevations.The soil water content can explain nearly 24.3%of the variation in ratios between respiration component,while ammonium nitrogen and nitrate-nitrogen together can explain 79.05%variation of Q₁₀.The Variation partitioning analyses results showed the soil properties have higher explanation than climate variables,respectively 28.3%and19.4%.(2)The characteristics of Pinus taiwanensis community mainly affect the leaf area index(LAI)through the photosynthetic carbon sequestration(Wco₂)of the community,and then regulate the litter production(P_L)and surface root biomass(S_root)to control the changes of E_RSand E_RH,respectively.Which is different to E_RAdirectly regulated by Wco₂.In addition,climate factors and the growth traits of Pinus taiwanensis explain 15.9%and38.7%of the annual flux of soil respiration components,respectively.Follow the mixed linear model analysis,the result shows that altitude,soil properties,and community characteristics can explain 73.3%E_RSand 71.8%E_RHas a whole,while the explanation for E_RAis only 53.5%.(3)Repeated measures analysis of variance found that the Double Litter addition(DL)weakened the influence of elevations on soil respiration rates.For most elevation sites,the Q₁₀increased under the DL treatment but decreased with the RL.Although there is no significant difference in the lignin and cellulose of litter among the different elevations,the phosphorus content of litter increases significantly with elevations.The main litter quality index for predicting the annual flux of soil respiration of Pinus taiwanensis in this study is ratios of carbon to phosphorus(C:P)and lignin to phosphorus(Lignin:P)and the best predictive indicators of Q₁₀are nitrogen content(TN)and the ratios of cellulose to nitrogen(Cel:N).The altitude and P-related quality network characteristics can account for the 76.8%E_RSvariations.In short,the variation of annual fluxes of soil respiration components affected by litter treatment mainly depends on changes in soil acid phosphatase activity and fungal and bacterial PLFAs content,while root removal treatment is regulated by ratio of soil microbial biomass carbon to nitrogen.(4)The root removal treatment(RL)regulates the variations of E_RS,E_RHand E_RAamong the different elevations by involving the ratios of microbial carbon to nitrogen(46.7%)and the acid phosphatase activity(12.7%).The control treatment(CT)regulates the content of Fungi PLFAs(39.6%),the RL regulates the acid phosphatase activity(36.5%),the content of bacterial PLFAs(12%),the double litter addition treatment(DL)regulates the acid phosphatase activity(45.9%)to affect E_RS,E_RL(the annual flux of litter removal),E_RDL(the annual flux of double litter addition),and E_LR(the annual flux of litter respiration)variations in different elevations.Therefore,root as the mainly carbon release part affect the different respiration components variation among the different elevations through the regulate the ratios of microbial biomass carbon to nitrogen and the acid phosphatase activity,while the litter manipulation is mainly through the acid phosphatase activity and the content of fungi PLFAs.In summary,given that the soil DOC,DON,and p H can significantly explain the variation of annual fluxes of different soil respiration components among the different elevations.The soil water content and ammonium nitrogen content can significance regulate the ratios of annual flux and Q₁₀changes,respectively.The E_RHis mainly driven by P_L,while E_RAmain directly regulate by Wco₂.In addition,E_RSand E_RHare stronger than E_RAin response to the comprehensive influence of altitude,soil properties,and community characteristics.Thus,the results indicate that soil properties and community characteristics(not climate variables)may be the main factors affecting the changes in soil respiration at different elevations.Although the litter quality that predicts the annual flux variation of soil respiration components is mainly related to the P content,the predictive index of Q₁₀changes main depends on the nitrogen content of the litter.In addition,phosphatase activity as a common factor significantly regulates the characteristics of soil respiration under litter manipulation and root removal treatments.These results indicate that the return of N and P content in litter and the soil microbial phosphatase activity may be the crucial factors to predict the changes in the soil carbon emission characteristics of Pinus taiwanensis in the future when the litter increased.