Effects Of Seasonal Freezing And Thawing On Soil Microbiological Properties In Zhalong Wetland

Soil microorganisms are the most important decomposers of wetland ecosystems and play an irreplaceable role in ecological processes such as nutrient cycling,material transformation,energy flow and environmental restoration,and can also serve as early warning indicators of changes within wetland ecosystems.This study took Zhalong Wetland as the research object,using phospholipid fatty acid method,chloroform fumigation method and microplate method to analyze the seasonal freeze-thaw period(initial freeze-thaw period,late freeze-thaw period,stable freeze-thaw period,early thaw period and late thaw period),to explore the soil microbiological properties'response mechanism to seasonal freezing and thawing processes under the background of global climate change,for in-depth analysis of the characteristics of soil quality evolution and ecosystems in Zhalong wetland and the restoration and protection of wetland ecosystem functions.The results of soil microbial phospholipid fatty acid content analysis showed that the total PLFA content of soil microorganisms ranged from 15.90 nmol·g^-1 to 22.16nmol·g^-1,and was significantly higher in the early freeze-thaw,early thaw,and late thaw periods than in the late freeze-thaw and stable freeze periods(P<0.05).The bacterial PLFA content accounted for 84.79%?86.51%of the total PLFA content,with the highest(18.92 nmol·g^-1)in the late thaw period and the lowest(13.48 nmol·g^-1)in the stable freeze period;the fungal PLFA content changes firstly and then decreases.The index of Shannon-Wiener diversity and Mc Intosh uniformity indices were both the highest in the late thaw period(3.000,6.437),while the Simpson index was highest in the stable freezing period(0.041).Principal component analysis indicated that seasonal freeze-thaw pronouncedly changed the soil microorganism community composition.The analysis of soil microorganisms biomass showed that the soil microbial biomass of carbon,nitrogen,and phosphorus was highest at the beginning of freezing and thawing,and lowest in the stable freezing period.Among them,the nitrogen in the soil microbial biomass has a tendency to first decrease and then increase,and the carbon and phosphorus in the soil microbial biomass have a tendency to increase and then decrease.The carbon-nitrogen ratio of soil microorganisms at the beginning of thawing was significantly higher than other periods(P<0.05),and the soil microbial nitrogen and phosphorus ratios were highest at the end of thaw(6.02,29.72)and lowest at the beginning of thaw(4.85)and the late of freeze-thaw(22.75),respectively.Analysis of soil extracellular enzyme activity showed that soil?-glucosidase was significantly higher in the early freeze-thaw period than in other periods(P<0.05),soil?-N-acetylaminoglucosidase first increased and then decreased,soil acid phosphatase was the highest in the early thaw period(169.95 nmol·g^-1·h^-1)and the lowest in the early freeze-thaw period(120.78 nmol·g^-1·h^-1),the activities of soil peroxidase and polyphenol oxidase showed a downward trend first,and then an upward trend.Soil ln(BG):ln(NAG)and ln(BG):ln(ACP)were highest at the beginning of freeze-thaw(1.65,0.68),while soil ln(NAG):ln(ACP)was highest at the stable freezing period(0.48).Principal component analysis indicated that seasonal freeze-thaw had a greater effect on extracellular enzyme activity in soils of Zhalong wetland.The results of redundant analysis showed that soil moisture content was significantly positively correlated with total PLFA,bacteria,Gram-positive,Gram-negative,actinomycetes,peroxidase and polyphenol oxidase(P<0.05).Soil total phosphorus,available phosphorus and available nitrogen were significantly positively correlated with fungi and?-N-acetylglucosaminidase(P<0.05).Soil?-glucosidase is mainly affected by the soil carbon to nitrogen ratio and organic matter.The soil carbon to nitrogen ratio was the highest in the early period of freezing and thawing(51.63),while both soil nitrogen to phosphorus ratio and carbon to phosphorus ratio were highest at the end of thaw(1.88,75.65).Correlation analysis showed that there was a important correlation between soil microbial load and environmental factors.Linear regression analysis showed that the chemical ratio of extracellular soil enzymes were closely related to soil p H,water content,total soil phosphorus,available nitrogen and available phosphorus.