Study On The Mechanism Of Hydrological Managements On The Soil Microbial Enzyme Activities And Communities In Restored Peatlands

Peatlands are important carbon reservoirs in terrestrial ecosystems and play important roles in the global carbon cycle.Since the 1950s,intensive human agricultural activities have drastically reduced the areas of peatlands worldwide,and their ecological functions have been under serious threat.Therefore,ecological restorations of degraded peatlands are urgently needed.The hydrological conditions of peatlands influence their biogeochemical cycles and maintain the structures and functions of peatland ecosystems.Adopting appropriate hydrological managements measures for peatlands hydrological restorations is the key to the rapid recovery of peatlands ecological functions.Soil microorganisms are the most active components of the soil,and their sensitivities to changes in soil water conditions is considered to be the most promising indicator for evaluating soil qualities.However,studies on the effects of different hydrological managements on soil microbial properties during peatland restorations are limited.In this study,we used different hydrological managements（low water level,alternating high and low,high water level）in restored peatlands in Changbai Mountains to reveal the differences in soil physicochemical properties under different hydrological managements,analyzed the effects of different hydrological managements on soil microbial enzyme activities and community structures in restored peatlands,and investigated the mechanisms of different hydrological managements on soil microbial properties in restored peatlands.The main findings of this study are as follows:（1）Soil water content（SWC）,soil organic carbon（SOC）,dissolved organic carbon（DOC）,total nitrogen（TN）and dissolved organic nitrogen（DON）in the study area showed that natural peatland>restored peatland>degraded peatland;p H and total phosphorus（TP）showed that degraded peatland>restored peatland>natural peatland;ammonium nitrogen（NH₄⁺-N）showed that restored peatland>degraded peatland>natural peatland.There were significant effects of different hydrological managements on soil physicochemical properties of restored peatlands,and the contents of SWC,p H,SOC,DOC,TN,NH₄⁺-N,and DON were significantly higher in alternating high and low water level and high water level restoration areas than in low water level restoration areas（p<0.05）.（2）Three hydrolase enzyme（β-1,4-glucosidase（βG）,β-1,4-N-acetyl-glucosaminidase（NAG）,and acid phosphatase（AP））activities in the study area showed natural peatland>restored peatland>degraded peatland;two oxidase enzyme（polyphenol oxidase（PPO）,peroxidase（PER））activities showed restored peatland>degraded peatland>natural peatland.There were significant effects of different hydrological managements on soil enzyme activities in restored peatlands,and the three hydrolase enzyme activities were significantly higher in the low water level（p<0.05）,alternating high and low water level restoration areas than in the high water level restoration area,and the two oxidase enzyme activities were significantly higher in the alternating high and low water level and high water level restoration areas than in the low water level restoration area（p<0.05）.Hydrological managements had no significant effects on the seasonal variation of soil enzyme activities in restored peatlands（p<0.05）.（3）Soil microbial biomass carbon（MBC）and microbial biomass nitrogen（MBN）contents in the study area showed that natural peatland>restored peatland>degraded peatland.Different hydrological managements had significant effects on soil MBC and MBN contents in restored peatlands（p<0.05）.Soil MBC and MBN contents in low water level restoration area were significantly higher than those in alternating high and low water level and high water level restoration area（p<0.05）.Seasonally,the highest values of soil MBC and MBN in natural and low water restoration areas and degraded peatlands occurred in July,and the highest values in alternating high and low and high water level restoration areas occurred in May.（4）Soil total phospholipid fatty acid（PLFA）,bacterial PLFA,actinomycete PLFA,and Gram-positive PLFA contents in the study area showed natural peatland>restored peatland（low water level）>degraded peatland.There were significant differences in PLFA contents of each soil type in the restored peatlands with different hydrological managements restoration areas,and the PLFA contents of each soil type in the low water level restoration area was significantly higher than that in the alternating high and low water level and high water level restoration area（p<0.05）.Meanwhile,hydrological managements affected the proportions of each soil PLFA type in total PLFA,and in general,it decreased the proportions of soil bacterial PLFA and fungal PLFA in total PLFA,but increased the proportions of soil actinomycete PLFA and Gram-negative PLFA in total PLFA,and all of them gradually approached the proportions of each PLFA type in total PLFA in natural peatlands.（5）Correlation analysis and RDA analysis showed that soil enzyme activities,MBC,MBN,microbial community structures were closely related to water level（WL）and soil physicochemical properties,where WL,SWC,and NH₄⁺-N were the main controlling factors affecting soil enzyme activities,TP and WL were the main controlling factors affecting soil MBC and MBN contents,and WL and NH₄⁺-N were the main controlling factors affecting soil microbial community structures.In summary,the applications of different hydrological managements to degraded peatlands significantly affected soil physicochemical properties,enzyme activities,microbial biomass,and microbial community structures.Among them,the lower water level environment significantly increased soil enzyme activities,MBC,MBN and soil PLFA content of each type,while the higher water level environment effectively increased soil carbon,nitrogen,phosphorus and other nutrient elements contents.Thus,it can be shown that the implementation of appropriate hydrological managements in degraded peatlands can change the availability of nutrients,which in turn affects the amount of soil microorganisms,enzyme activities and microbial community structure in restored peatlands.Therefore,low water level management should be selected for peatland restoration at the early stage of restoration,which is most conducive to soil microbial growth and metabolism and the establishment of dominant vegetation communities,and high water level management at the later stage of restoration,which is conducive to increasing soil nutrient content and controlling the growth of non-target species,thus enhancing the soil carbon"sink"function of the soil.This will enhance the soil carbon"sink"function and accelerate the restoration of peatland ecosystem functions.