Effects Of Drying And Rewetting On Phosphorus Release And Microbial Community Of Sediment In Water-level Fluctuation Zone

Sediment in water-level zone has unique ecological environmental and geographical conditions,and is a key area for energy and material transfer between water and land.The bacterial community structure and physicochemical properties of sediment in water-level fluctuation zone were changed under the action of dry-wet alternation.In this paper,bacterial diversity and physicochemical properties of sediment in the fluctuation zone of Nansi Lake were simulated under different frequencies of wetting and drying.The morphological changes of phosphorus in sediment were analyzed by SMT method;The characteristics of bacterial communities in sediment during dry-wet alternation were studied by high-throughput sequencing technology,the relationship between bacterial community and physicochemical properties of sediment under alternate wetting and drying conditions was discussed,the main bacterial populations affecting the release of phosphorus from sediment in water-level-fluctuation zone were identified.The results are as following:（1）The physicochemical properties of sediment in water-level-fluctuation zone showed different trends during drying and alternation.The p H and dissolved organic carbon（DOC）content in sediment were higher in the drowning period than in the drying period,and oxidation reduction potential（ORP）was higher in the drying period than in the drowning period.The p H of sediment in constant humidity group was different from that in high frequency group and low frequency group,and showed a slow rising trend.After 112 d of submergence,the sediment was alkaline.ORP showed a steady trend in the late period of submergence.DOC showed a dynamic equilibrium during submergence.（2）The alternation of wetting and drying promoted the release of phosphorus from sediment in water-level fluctuation zone,and had different effects on different phosphorus forms in sediment.TP,IP and HCl-P in sediment showed a decreasing trend during the dry-wet alternating process.Frequent dry-wet alternating promoted the release of phosphorus in the sediment.Meanwhile,the release potential of TP,IP and HCl-P in the sediment with high frequency of dry/wet alternation was stronger than that in the low frequency dry/wet alternation and constant humidity groups.TP,IP and HCL-P in high frequency sediment decreased by 11.0%,12.2%and 12.9respectively.TP and IP in low frequency sediment decreased by 5.98%and 3.2%,respectively.However,OP and NaOH-P did not change significantly during wetting and drying.（3）The abundance of microbial community in sediment in water-level-fluctuation zone change during dry-wet alternation.According The number of OTU_Sspecies increased by 4,61 and 226,respectively,under the condition of high-frequency dry-wet alternation and low-frequency dry-wet alternation and constant humidity control,and the OTU_Sspecies under constant humidity inundation was the highest.Frequent dry-wet alternation was not conducive to maintaining microbial diversity in the sediment in the water-level fluctuation zone.The diversity analysis of Alpha index also showed that dry-wet alternation reduced the diversity index of sediment in the water-level-fluctuation zone.The maximum Shannon index of high-frequency group and low-frequency group was 6.332 6.390 and 6.585,respectively,and the maximum Chao index was 3218.320 3240.058 and 3520.836,respectivelyThe bacterial community structure of sediment in water-level-fluctuation zone remained stable during the dry-wet alternation.High-throughput sequencing shows that the main phyla in the sediment samples were Proteobacteria,Actinobacteria,Acidobacteria,Chloroflexi and Gemmatimonadetes,Firmicutes,Myxococcota,Bacteroidota,Cyanobacteria,Methylomirabilota,Desulfobacterota,Nitrification,Nitrospirae and Verrucomicrobia.At the level of class classification,the main bacteria are Gammaproteobacteria,Alphaproteobacteria,Actinobacteria,Gemmatimonadetes.The bacterial community composition of high frequency group and constant humidity group was the same as that of low frequency group.The dominant phyla were Actinobacteria,Firmicutes and Myxococcota during submerge conditions,and WPS-2 during drought conditions.（4）Through the analysis of the relationship between the bacterial species in the bottom mud at the level of phylum classification and different forms of phosphorus,Proteobacteria,Actinobacteria,Bacteroidota,Cyanobacteria,Verrucomicrobia are correlated with phosphorus in sediment.Cyanobacteria and Verrucomicrobia were significantly correlated with TP,IP and NaOH-P.