| Changes in the Three Gorges reservoir water-level is regulated by the scheduling,and periodic appeared alternating in riparian zone is caused by water-level fluctuations,causing riparian zone to become a hot issue of biogeochemical cycle in the reservoir area.The soil in riparian zone is effected not only by gravitational erosion and water wave impact which is caused by water-level fluctuations,but also by rainfall erosion.Therefore,resulting in the changes of soil physical and chemical properties and microbial characteristics in the riparian zone,which have an important role in material recycling and energy flowing in the riparian zone.Soil microorganism is an important component part of soil ecosystem,playing a key role in maintaining of ecological balance.However,few studies had reported the changes of soil microbial community structure and function diversity in the riparian zone of the Three Gorges reservoir area.The knowledge about how the microbial community structure and function respond to different water-level fluctuation is significant in this study.Soil microorganism is the sensitive indicator for assessing soil quality and could timely indication of changes in soil environmental quality.In this study,the surface soil of Tongzhuang River was selected as the research object.According to different water-level fluctuation to set four water status:(1)longer inundation(LI)at 145-155 m above sea level,(2)middle inundation(MI)at 155-165 m above sea level,(3)shorter inundation(SI)at 165-175 m above sea level,(4)never inundation(NI)at 175-185 m above sea level was used as a control.Using phospholipid fatty acid(PLFA)and Biolog-ECO to analysis changes of soil microbial community structure and function diversity under different water-level gradients,studying the relationship between soil microbial community structure and function and soil physical and chemical properties by redundancy analysis,revealing key driving factors of changes in soil microbial community structure and functional diversity in the riparian zone.The main results are as follows:1.Soil microbial communities were abundant in the areas with middle inundation and shorter inundation,and the utilization rate of carbon source was stronger.2.The soil microbial activity was higher in the Three Gorges reservoir area with shorter inundation,and the activity of soil microorganism showed a downward trend with the extension of inundation time.3.The dominant species of soil microorganisms in riparian zone were bacteria,followed by community structure were Bacteria> Actinomycetes> Fungi> Protist;The contents of total PFLA,Actinomycetes,Gram-positive bacteria,Gram-negative bacteria and total bacteria in the soil microbial community were MI> NI> SI> LI;Soil dominant PLFA had 6: 0 10-methy,18: 0 10-methyl,16: 1 ?7,18: 1 ?7c,15: 0 iso,15: 0 anteiso,16: 0 iso,18: 1 ?9c and 16: 1 ?5c.4.Carbohydrates were mainly used carbon sources in the riparian zone of the Three Gorges reservoir area of soil microorganism,including D-galactose ?-lactone,D-xylose,i-erythritol,D-mannitol,N-acetyl-D-glucosamine,D-glucosamine acid,D-cellobiose,glucose-1-phosphate and ?-D-lactose.5.Soil water-level fluctuation,organic carbon,total nitrogen,total phosphorus and soil moisture were positively correlated with Gram-positive bacteria,Gram-negative bacteria,Fungi,Protist,and Actinomycetes;but p H had a negative correlation with soil microorganisms.RDA analysis indicated that soil organic carbon and p H could be the driving factors affecting the soil microbial community structure in the riparian zone;water-level fluctuation and p H could be the driving factors affecting the function diversity of soil microbial communities in the the riparian zone.6.Soil organic carbon was significantly positively correlated with carbohydrate,p H was negatively correlated with carbohydrate,carboxylic acid,amino acid and phenolic acid.Carbohydrate and carboxylic acids were positively correlated with gram-negative bacteria,gram-positive bacteria,bacteria,fungi,protozoa and AM fungi;amines and polymers were positively correlated with soil microbial community structures,while phenolic acids were not correlated with soil microbial community structures.In a word,the length of soil inundation time had changed the soil physical and chemical environment,the structure and composition of the microbial community.Soil microorganisms in the areas with middle and shorter inundation time in the riparian zone were conducive to the growth and metabolism.The longer of soil inundation time,the significantly reduced the metabolic capacity of carbon source.The influence mechanism of water-level change on soil microbial community structure and metabolic diversity were revealed in order to provide scientific theoretical basis for the protection and improvement of the Three Gorges reservoir area. |
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