Population Characteristics And Ecological Restoration Potential Of The Seagrass Ruppia Sinensis In Temperate Coastal Areas

Seagrass is a kind of marine angiosperms that are widely distributed in temperate and tropical regions of the world.Seagrass meadow is known as one of the three key marine ecosystems with mangrove and coral reefs.Ruppia is a kind of seagrass widely distributed in shallow waters such as tropical and temperate coasts,lagoons,salt marshes,etc.It is an important part of these water ecosystems,and undertakes the significant ecological functions such as habitats establishment and regulation of water-sediment environments.With the intensifying climate change and human impact,Ruppia has been declining at an alarming rate worldwide with numerous seagrasses.We investigated the current status of the distribution of Ruppia in temperate coastal regions of China,analyzed the influence of major environmental factors on the seed germination of R.sinensis and its favorable preservation conditions,explored the formation conditions of R.sinensis population in different life history types and their interactions with the substrate environment,and compared their stability under extreme dry inhibition.The tolerance of R.sinensis on Cu and Cd contamination and relative toxicity effects were investigated.1 Investigation on the distributing status of Ruppia in ChinaThis study investigated the distribution status of R.sinensis in the coastal areas from Liaoning to Zhejiang in China.It was concluded that marine aquaculture ponds,saltwater lagoons,ditches,wetland park,and intertidal area were the types of distribution environment in the temperate coastal regions of China,especially in aquaculture ponds.Several R.sinensis populations recorded in previous documents had disappeared in our revisiting investigation.After comprehensive analysis of the literature records and field survey information,it is believed that the disturbance of human activities is the main reason affecting the distribution of R.sinensis.2 Population characteristics of R.sinensis in Yellow River DeltaIn this study,we investigated the influence of desiccation on the sediment seed bank and population recruitment in a R.sinensis seagrass meadow where the surface sediment occasionally experiences long-term air exposure in the Yellow River Delta.Results showed that habitat desiccation had significantly impacted the R.sinensis population.However,a considerable number of sediment seeds survived the long-term desiccation of the surface sediment.After a 5-month period of desiccation(from December 2017 to April 2018)of the surface sediment,followed by re-submersion,the R.sinensis seedling density in May 2018 was 1360.86±330.66 seedlings/m~2,which was similar to that in March 2017.Thus,desiccation appeared to have retarded seed germination and seedling establishment.These results indicated that sediment R.sinensis seeds can survive the long-term desiccation of their habitat.Unlike most seagrass species,we observed for the first time that R.sinensis seeds in sediment exhibited considerable tolerance and adaptability to habitat desiccation.Our results provide new insights into the resilience of R.sinensis populations affected by desiccation and supple the Ruppia populations characteristics.Plant-soil interactions influence vegetation status and sediment characteristics.Annual and perennial life cycles are common in the same submerged aquatic angiosperm species,yet relationships between the life cycle strategies and sediment characteristics are poorly understood.This study aimed to investigate the interactions between different life cycles of the seagrass species R.sinensis and sediment characteristics including sediment nutrients.We surveyed two R.sinensis populations in the Yellow River Delta with different life cycles.The biomass of their peak growing seasons and their seasonal seed bank size were applied to evaluate their population status and potential recruitment capacity.Nine parameters were measured to assess sediment nutrient composition and variability.We found relatively higher biomass and more intensive seed bank sizes in annual life cycle R.sinensis populations.The appearance of overlying water impacted the surfer sediment moisture content and then R.sinensis life cycle strategies.Moreover,the appearance of R.sinensis shoots significantly impacted total nitrogen and organic matter in their habitat.Our results indicate that different life cycle strategies have different resilience capacities after exposure to desiccation of the habitat,while the appearance of R.sinensis impacted sediment nitrogen and organic matter features.3 Effects of environmental factors on seed germination of R.sinensisIn this study,we investigated the effects of temperature and salinity on seed germination and seedling establishment of R.sinensis seeds collected from northern China.The effects of seven salinities(0–50 psu)and six water temperatures(0-30°C)on seed germination were investigated to identify the environmental conditions that could potentially limit survival and growth.We found that:(1)optimum seed germination was salinity 5 psu at 30°C;(2)high salinity(salinity 40–50 psu)and low temperature(0°C)significantly inhibited seed germination,but which significantly increase after transferring to optimum conditions;(3)seed germination with increasing temperature showed a bimodal pattern at suitable salinities(5-10 psu);4)storing seeds at high salinities(40-50 psu)or low temperature(0°C)promoted germination after transferal to optimal germination conditions.(5)Temperature had the significant influence on the germination of R.sinensis,however,salinity didn't.These findings may serve as useful information for R.sinensis habitat establishment and restoration programs.4 The long-term preservation methods of R.sinensis seedsThe seeds of Ruppia are ideal materials for its population restoration.Collecting mature Ruppia seeds during its breeding season and save them to the artificial seed bank,which can make full use of them for subsequent restoration.The low temperature,high salinity and desiccation all effectively inhibited the germination of R.sinensis seeds.Different temperature,salinity,and desiccation conditions were adopted to reserve R.sinensis seeds in experiments of this section.From the results of the previous part,we can know that certain low temperature,high salt and dry conditions can inhibit the seed germination of R.sinensis without reducing their activity,so the experiment of this part attempts to use different high salinity and low temperature conditions for its long-term preservation in water.Moreover,R.sinensis seeds were preserved at different temperatures in dry air.By comparing the viability of seeds after 9 months of storage with two preservation methods and their internal energy substances,it is considered that the wet preservation method of 0°C and 30-40 psu salinity conditions is fit for the long-term preservation of R.sinensis seeds,and the best environmental condition of dry preservation is 5?and relative humidity of 33±10%.Although the method of dry preservation will reduce the seed vigor to a certain extent,it is also a feasible method for long-term preservation of R.sinensis seeds.The above results provide corresponding basic knowledge for establishing the artificial seed bank of R.sinensis.5 The tolerance of R.sinensis on Cu and Cd pollution and relative toxicity effectsRuppia is tolerant not only of a wide salinity range,but also of high concentrations of trace metals.However,the tolerance of its early life stages to such trace metal exposure is unclear.Thus,the current study investigated the trace metal-absorbing capacity of three different life history stages of R.sinensis,a species that is widely distributed in China,observing toxic symptoms at the individual,subcellular,and transcription levels.The seedling period was the most vulnerable,with visible toxic effects at individual level in response to Cu 50?M and Cd 500?M after 4 days of exposure.The highest concentrations of trace metals occurred in the vacuoles and cytoplasmic structures of aboveground tissues.Genes related to signal identification and cellular components were significantly downregulated after 4 days of exposure to Cd.These results provided information relating to the strategies evolved by R.sinensis to absorb and isolate trace elements,and evaluated the phytoremediation potential of this species.