Particle size shapes the prokaryotic microbial communities in mangrove sediments:A case study of Sanya,China

The prokaryotic microbial communities in the sediments play crucial roles in the ecological functions of mangrove ecosystems.Therefore,the environmental factors that affect the structures of these prokaryotic microbial communities could indirectly participate in the regulation of mangrove functions,which is of great value for mangrove studies.The particle size(PS)of soils is recently demonstrated as a key environmental factor for shaping the microbial communities;however,this hypothesis has rarely been tested for mangrove environments.A case study of three tropical mangroves from Sanya,China was performed in this work to assess the influence of PS on the prokaryotic microbial community structures of bacteria,archaea,diazotrophs,and denitrifiers in the sediments.Results showed the variability in the spatial scale and the stability in the temporal scale for the prokaryotic communities,indicating that the tropical mangrove sediments could be a versatile but stable environment.Among the collected environmental factors,PS,salinity,and humidity had the greatest impacts,and PS mostly affected the structures of these prokaryotic communities based on its highest R^2 values of canonical correspondence analysis,Mental test,and linear fitting(p≤0.05).Furthermore,PS was positively correlated with the diversity and abundance of diazotrophic communities and negatively correlated with the abundances of methanogenic communities including Methanobacteriaceae,Methanospirillaceae,Methanoregulaceae,and Methanosaetaceae.Former studies show the increasing trend of PS caused by the rise of sea level and the intensification of human activities.Therefore,our findings indicate that PS could be a potential intermediate that links climate change and human activities with the possible ecological function migration of mangroves;meanwhile,the increase of PS could in turn release the stress of these environmental changes by increasing the abundance and diversity of the diazotrophic community and decreasing the abundances of methanogens.

Microplastic pollution and enrichment of distinct microbiota in sediment of mangrove in Zhujiang River estuary,China

The microbial communities colonized on microplastics(MPs)have attracted widespread attention.However,few studies focused on the MPs impacts on mangrove ecosystems,particularly on bacterial communities.We investigated the MPs pollution in mangrove of Zhujiang(Pearl)River estuary(ZRE).To study the potential risk posed by MPs to the mangrove ecosystems,the differences in bacterial communities,functions,and complexity between MPs and sediment samples were reported for the first time.Microplastics(2991±1586 items/kg dry weight(dw))in sediment were mainly fibers and polyethylene,mostly transparent,and in size less than 0.5 mm.Bacterial communities and functions significantly differed from MPs in mangrove sediment.Compared with sediment,MPs significantly enriched members of Proteobacteria,Bacteroidetes,and Actinobacteria,as well as the bacteria associated with plastic-degrading and human diseases on their surface,suggesting that microbial communities on MPs may promote MPs degradation and the spread of diseases,posing potential risk to mangrove ecosystems and human health.Although bacteria on MPs exhibited a lower diversity,the co-occurrence network analysis indicated that network of bacteria colonized on MPs was bigger and more complex than those of mangrove sediment,illustrating that MPs can act as a distinct habitat in this special ecosystem.This study provides a new perspective for increasing our understanding of microplastic pollution in mangrove ecosystems.

Anaerobic biodegradation of PAHs in mangrove sediment with amendment of NaHCO_3

Mangrove sediment is unique in chemical and biological properties. Many of them suffer polycyclic aromatic hydrocarbon（PAH） contamination. However, the study on PAH biological remediation for mangrove sediment is deficient. Enriched PAH-degrading microbial consortium and electron acceptor amendment are considered as two effective measures. Compared to other electron acceptors, the study on CO2, which is used by methanogens, is still seldom. This study investigated the effect of Na HCO3 amendment on the anaerobic biodegradation of four mixed PAHs, namely fluorene（Fl）, phenanthrene（Phe）,fluoranthene（Flua） and pyrene（Pyr）, with or without enriched PAH-degrading microbial consortium in mangrove sediment slurry. The trends of various parameters, including PAH concentrations, microbial population size, electron-transport system activities, electron acceptor and anaerobic gas production were monitored. The results revealed that the inoculation of enriched PAH-degrading consortium had a significant effect with half lives shortened by 7–13 days for 3-ring PAHs and 11–24 days for 4-ring PAHs. While Na HCO3 amendment did not have a significant effect on the biodegradation of PAHs and other parameters, except that CO2 gas in the headspace of experimental flasks was increased.One of the possible reasons is that mangrove sediment contains high concentrations of other electron acceptors which are easier to be utilized by anaerobic bacteria, the other one is that the anaerobes in mangrove sediment can produce enough CO2 gas even without adding Na HCO3.

Impact of mangrove vegetation on seasonal carbon burial and other sediment characteristics in the Vellar-Coleroon estuary, India

This work quantified the total carbon and 12 other sediment characteristics at 10 soil depths, in planted and or natural mangrove forests in comparison with non-vegetated soil for four seasons of the year 2009-2010 in the Vellar-Coleroon estuarine complex, India. The sedi- ment characteristics varied significantly between mangrove-vegetated and non-vegetated habitats or seasons of analysis, but not between soil depths. The mangrove sediments were rich in total carbon and total or- ganic carbon as compared to non-mangrove sediments （p 〈0.01）. Total carbon was 98.2% higher in mature mangroves and 41.8% in planted mangroves than that in non-mangrove soil. Total organic carbon was as much as 2.5 times greater in mature mangroves and 2 times greater in planted mangroves than that in unvegetated soil. Carbon contents also varied many fold by season. Total carbon content was 8.6 times greater during pre-monsoon, 4.1 times greater during post-monsoon and 2.5 times greater during monsoon than during summer （P〈0.01 in all cases）. Similarly, total organic carbon was 5.9 times greater during pre-monsoon, 3.1 times greater during post-monsoon and 69% greater during monsoon than during summer. In general, higher levels of sediment carbon were recorded during pre and post-monsoon seasons than during other seasons. Total carbon concentration was correlated negatively to temperature, sand and phosphorus （P 〈0.01）; positively correlated with redox potential, silt, clay, C/N ratio, potassium （P 〈0.01） and nitrogen （P〈0.05）; but not correlated with soil depth, pH or salinity. This work revealed that the carbon burial was rapid at the annual rate of 2.8% for total carbon, and 6.7% for total organic carbon in mangrove-planted sediment. Cleating of mangroves can result in significantly and rapidly reduced carbon stores.Our study highlights the importance of natural and plantation mangrove stands for conserving sediment carbon in the tropical coastal domain.