The Differences In Soil Microbial Communities Between Swamp Meadow And Alpine Meadow On The Tibetan Plateau And Their Function In The Utilization Of Rhizodeposited Carbon

As a transition zone between land area and aquatic area,wetland plays an important role in conserving water sources,purifying the environment,regulating climate and carbon storage.The Zoige wetland located on the eastern edge of the Tibetan Plateau is the largest plateau swamp wetland in China.In recent years,the Zoige wetland has been seriously degraded due to the climate change and interference from human activities,and once reversed succession from swamps and swamp meadows to alpine meadows and even deserts.As a key factor in the decomposition and nutrient cycling of terrestrial ecosystems,soil microorganisms are very sensitive to environmental changes and are important indicators to measure soil quality and ecosystem stability.During the process of wetland degradation,the soil microbial community has changed correspondingly due to changes in environmental conditions,and the microbial groups located at different depths of the soil may have different responses to wetland degradation.However,rare studies focused on the changes of soil microbial community at different depths in the process.Here,we focused on soil microbial communities at different depths in swamp meadows and alpine meadows on the Tibetan Plateau,through the ¹³C-labeled phospholipid fatty acid detection technology(SIP-PLFA),explored the differences in soil microbial communities at different depths in swamp meadow and alpine meadow,the temporal dynamics of the year,and the distribution of rhizodeposited carbon among different soil microbial groups.The main results are as follows:(1)The total microbial biomass,gram-positive bacteria,gram-negative bacteria and fungi biomass of swamp meadow were significantly higher than that of alpine meadow,while there was no significant difference between actinomycetes and AM fungi in swamp meadow and alpine meadow.(2)In 0-5cm,5-15cm and 15-30cm soil layers,the ratios of the gram-negative bacteria,fungi and F/B in swamp meadow were significantly higher than that in alpine meadow,while the ratios of AM fungi,gram-positive bacteria and GP/GN were significantly lower than that in Meadow.(3)The physical and chemical properties of soil had significant impact on the soil microbial communities in swamp meadow and alpine meadow.The soil water content,organic carbon and total nitrogen had significant positive correlation with each microbial group,and the soil p H had significant negative correlation with each microbial group.(4)The soil microbial communities of swamp meadow and alpine meadow showed obvious seasonal trend,and the soil microbial biomass of swamp meadow was significantly higher than that of meadow,and the interannual changes were also greater.The total microbial biomass and the biomass of each microbial group were higher in spring and autumn,followed by summer,and the lowest in winter.The biomass of most of the microbial groups is the highest in autumn,while that of AM fungi is the highest in spring.(5)After ¹³C labeling,the?13C value of fungi and AM fungi increased rapidly in the initial stage of labeling(day 1),then decreased rapidly after 4^th day,and stabilized;while the?13C values of the gram-positive bacteria,negative bacteria and actinomycetes gradually increased over time.These results reflected the differences in the utilization of the rhizodeposited carbon among different soil microbial groups.In summary,the soil microbial community in swamp meadow had a higher F/B and the stability,while the soil ecosystem of meadow was dominated by bacteria,especially the content of gram-positive bacteria was higher,and gram-positive bacteria tended to use the more stubborn carbon in the soil,which will increase the ability to decompose organic carbon during the degradation of swamp meadows to meadows.Isotope labeling experiments indicate that fungi and AM fungi might be the first microbial groups to use the rhizodeposited carbon in the short term,while Bacteria such as the gram-positive bacteria,the negative bacteria and the actinomycetes gradually obtain the rhizodeposited carbon through the turnover of other microorganisms(such as fungi and AM fungi).The above result can provide important scientific basis for the restoration of the swamp meadow ecosystem of the Tibetan Plateau,the structural changes of soil microbial communities and the research of soil carbon cycle.