Microbial Community Dynamics In Seagrass Meadow And Marine Farm Sediments And Driving Factors

The coastal zone is one of the ecosystems with the highest productivity and biodiversity on earth,and it is also one of the regions strongly affected by human activities.The coastal habitats are complex,including seagrass meadows,mangroves,and marine farms.Coastal sediments are important sites for organic matter burial,nutrient regeneration and greenhouse gas emission,where microorganisms play an important role in benthic ecology and chemical cycle.The sediment physical and chemical properties are affected by plant colonization and seasonal changes.In seagrass meadows,seagrass growth and photosynthesis are affected by seasonality,which may affect benthic microbial diversity and biogeochemical functions.In addition,due to the strong interference of human activities?economic animal and plant breeding,etc.?,the seawater in marine farms is usually eutrophic,and a large amount of cultivated animal feces is enriched on the seabed.Microbes degrade organic matters consuming oxygen and leading to hypoxia in summer with high temperature.However,the seasonal dynamics of microbial community structure,diversity and abundance in seagrass meadow sediments,and the response of microbes during hypoxia in marine farm sediments remained poorly understood.In this work,sediment archaea and bacteria community structure,diversity and abundance in the seagrass?Zostera marina?meadow of the Swan Lake Nature Reserve in Shandong Rongcheng and Muping marine farm were investigated through 16S r DNA high-throughput sequencing and real-time q PCR.Meanwhile,the physical-chemical properties and hydrological factors were determined to find the key factors regulating the dynamics of microbial commnities.The main findings were as follows:1. The archaeal community in the surface sediments of the seagrass meadow was mainly composed of Woesearchaeota?48.94%?,Thaumarchaeota?23.48%?,Bathyarchaeota?14.83%?,and Euryarchaeota?3.14%?.The dominant subgroups of Woesearchaeota included Woese-5b?32.79%?,Woese-5a?1.75%?,Woese-25.?1.32%?and Woese-Other?5.38%?,and the dominant subgroups of Bathyarchaeota were Bathy-6?6.88%?,Bathy-8?2.84%?and Bathy-17?2.5%?.Seasonality was the main driving force for the dynamic change of archaeal community structure and abundance:seasonality had significant impacts on archaeal?and?diversities?P<0.05?;in spring and winter,archaeal?diversity index and 16S r RNA gene copies were significantly higher than that in summer and autumn;meanwhile,the archaeal metabolic potential in winter was stronger than that in summer and autumn.RDA analysis showed that archaeal community structure was significantly correlated with salinity,temperature,p H and total nitrogen?P<0.05?.Seagrass colonization promoted archaeal 16S r RNA gene copies?P<0.05,t-test?,and reduced the?diversity.2. The bacterial community of seagrass meadow sediments was dominated by Proteobacteria?64.63%?,and followed by Actinobacteria?8.44%?,Bacteroidetes?8.15%?,Chloroflexi?5%?,Acidobacteria?2.27%?,Planctomycetes?2.16%?and Firmicutes?1.97%?.Seasonality was also the main driving force for the dynamics of bacterial community structure and abundance:it had a significant influence on bacterial?diversity?P<0.05,ADONIS?;the seasonal trend of bacterial?diversity was spring>summer>autumn>winter?P<0.05,ANOVA?;the bacterial 16S r RNA gene copies in spring and winter were significantly higher than those in summer and autumn;the bacterial metabolic potential was much stronger in spring and winter than that in summer and autumn.RDA analysis showed that the bacterial community was significantly correlated with salinity,p H,temperature and iron?P<0.05?.Seagrass colonization had no significant effect on bacterial 16S r RNA gene copies,but significantly reduced?diversity?P<0.05?and dramaticly influenced the?diversity?P<0.05,ADONIS?.3. In the sediment columns of the seagrass meadow,bacterial and archaeal communities and abundances presented obvious vertical patterns:the relative abundance of Thaumarchaeota significantly increased with increasing sediment depth,while that of Deltaproteobacteria significantly decreased with increasing sediment depth?P<0.05,ANOVA?;depth had no significant effect on archaeal and bacterial?and?diversities?P>0.05?;the 16S r RNA gene copy numbers of bacteria and archaea decreased with the increasing sediment depth,and the bacterial copy numbers in the 5-cm layer was significantly higher than those in the 20-cm and 30-cm layers?ANOVA test,P<0.05?.4. In the Muping marine farm sediments,the archaeal community was dominated by Thaumarchaeota?58.55%?,and followed by Bathyarchaeota?19.34%?,Woesearchaeota?16.76%?,Euryarchaeota?1.54%?and Lokiarchaeota?1.30%?.During the hypoxia,archaeal?diversity was lower in the high oxygen(H,DO>5 mg L^-1)group than that in the middle(M,3<DO?5 mg L^-1)and low(L,DO?3 mg L^-1)oxygen groups;archaeal 16S r RNA gene copy numbers were highest in M group than in H and L groups.The RDA results showed that the archaeal community structure was significantly related to DO,DIN and TOC?P<0.05?.5. Among the benthic bacterial community of Muping marine farm,the dominant phylum was Proteobacteria?62.28%?,and followed by Actinobacteria?12.77%?,Acidobacteria?5.69%?,Bacteroidetes?4.7%?,Chloroflexi?4.4%?,Gemmatimonadetes?2.52%?,Firmicutes?1.48%?,Lacecibacteria?1.21%?and Nitrospirae?1.19%?.During the hypoxia,bacterial?diversity significantly increased with decreaseing DO level,and the highest value was in L group?P<0.05,ANOVA?;the impact of hypoxia on bacterial 16S r RNA gene copy numbers was not significant?P>0.05,ANOVA?,and were least in M group.RDA results showed that the bacterial community structure was significantly related to DO,temperature,and TOC?P<0.05?.In general,in seagrass meadow sediments,seasonalinty was the main driving force for regulating archaeal and bacterial community structure.During the process of hypoxic event,the bottom water oxygen content,temperature,and sediment organic matter content?TOC and DIN?were the main driving forces for regulating benthic archaeal and bacterial community structures.