| Peatland soil is an important carbon（C）pool,but it usually lacks nitrogen（N）,phosphorus（P）,which limits the growth of microorganisms in the soil.To obtain sufficient NP,microorganisms will take certain strategies to decompose organic matter,which will lead to changes in soil organic carbon（SOC）.Therefore,nutrient limitation is the key to predict changes in SOC.At present,soil,ecoenzyme,and microbial biomass C:N:P stoichiometries are widely used to reveal microbial nutrient limitations in soil.However,it is unclear which stoichiometry can better indicate nutrient limitations and predict changes in soil organic carbon（SOC）content.In addition,N input caused by N deposition can change the nutrient limitations of microbes in soil,leading to changes in soil C content.However,in the past,NH4NO3 was mostly used to simulate N deposition,ignoring the impact of N deposition morphology on SOC.Therefore,it is necessary to explore the indicator effect of soil,ecoenzyme,and microbial biomass C:N:P stoichiometries on microbial nutrient limitation in peatland soil and the prediction effect on the change of SOC.At the same time,explore the relationship between N deposition forms and SOC content change,and clarify the change of C content in peatland soil under different N form inputs.This study took different soils in Zoige peatland as the research object,collected samples in different seasons and at different depths,and explored whether the soil,microbial biomass,and ecoenzyme C:N:P stoichiometries revealed the consistency of soil nutrient limit status,and evaluated the relationship between the three C:N:P stoichiometries and SOC.On this basis,exploring the impact and potential causes of N form on SOC through laboratory simulation of N input.The results show that:（1）Soil C:N:P and ecoenzyme C:N:P stoichiometries indicated P limitation,while microbial biomass C:N:P stoichiometry indicated N limitation in Zoige peatland.The path analysis results showed that the direct impact of microbial biomass C:N:P stoichiometry on SOC（0.44）was higher than that of soil and ecoenzyme C:N:P stoichiometries（both 0.32）.At the same time,the index of H′>1 indicated that the microbes were strongly homeostasis,and the microbial biomass C:N:P stoichiometry was in a relatively balanced state.In addition,the correlation between SOC and N and N acquisition ecoenzymes is stronger than that with P and P acquisition ecoenzymes,further revealing the important role of N in the change of SOC content.The above results indicated that the microbial biomass C:N:P stoichiometry may better reveal the nutrient limitation status and C dynamics in the Zoige peatland ecosystem.（2）The addition of NO3--N increased p H and dissolved organic carbon（DOC）content;decreased the contents of SOC,microbial biomass carbon（MBC）and microbial biomass nitrogen（MBN）;and inhibited the activities ofβ-glucosidase（BG）,β-1,4-N-acetyl-glucosaminidase（NAG）and leucine aminopeptidase（LAP）,increased the activities of alkaline phosphatase（AKP）.The change in soil’s physical and chemical properties has affected the composition of microbial community structure.At the phylum level of fungi,the relative abundance of Ascomycota was decreased.However,it increased the relative abundance of Basidiomycota and Monoblepharomycota.At the phylum level of bacteria,the relative abundances of Proteobacteria,Actinobacteria,Acidobacteria,Gemmatimonadetes,and Nocardioides were increased.The path analysis results showed that the NO3--N addition caused the reduction of SOC by changing the soil’s physical and chemical properties（p H and DOC）and microbial community structure.（3）The addition of NH4+-N increased SOC,decreased the contents of p H,DOC,MBC,MBN,and microbial biomass phosphorus（MBP）,increased the activities of NAG and AKP,and inhibited the activities of BG and LAP.Soil acidification and the changes in soil physical and chemical properties caused by it have affected the composition of microbial community structure.At the phylum level of fungi,the relative abundance of Ascomycota was decreased.However,it increased the relative abundances of Basidiomycota,Monoblepharomycota,and Nocardioides.At the phylum level of bacteria,the relative abundances of Proteobacteria,Bacteroidetes,Actinobacteria,and Geobacterium.The path analysis results showed that the NH4+-N addition caused the increase of SOC by causing soil acidification,changing soil physical and chemical properties and microbial community structure.This study showed that microbial biomass C:N:P stoichiometry can more accurately indicate the soil microbial nutrient limitation status and predict the change of SOC content,revealed the potential impact mechanism of N addition forms on SOC,provided a theoretical basis for predicting the change of soil C content in peatland soil. |
