Relationships Between Spatiotemporal Distribution Of Salt Spray Deposition And Growth Status Of Coastal Greening Plants

Coastal areas with sea and land properties are dynamic and complex natural environments,which make the coastal greening more specific.It needs to take into account the impact of marine environment and the continental environment on plants,and the main problem faced by coastal greening is from the air and soil salt damage to plants.At present,the studies on salt spray worldwide are focused on the physiological mechanism of salt spray stress,and the screening of salt-tolerant plant resources.However,few studies focus on the spatiotemporal distribution of salt spray deposition as well as exploration of salt spray hazard to plants and counter measures through practical greening projects.This study takes the coastal zone at Gulei Peninsula,Fujian,where the plants suffer from salt spray seriously,as the example.A tracking survey was conducted between May 2016 and March 2017 through four seasons to monitor salt spray deposition,environmental factors and growth of greening plants.The temporal and spacial distribution of salt spray deposition and the influence of salt spray deposition on the plants in the field were analyzed by combining the meteorological data such as rainfall,relative humidity and wind speed in the area.The main environmental factors were studied through installations of salt spray deposition cylinders and small anemometers at different distances from the coastline.In addition,a total 10 species including Hibiscus tiliaceus,Phoenix sylvestris,Ficus altissima,Alstonia scholaris,Erythrina×sykesii,Ficus religiosa,Hibiscus rosa-sinensis,Fagraea ceilanica,Duranta erecta and Catharanthus roseus,were selected to study the impacts of different coastline distances,seasons and the protection of forests and other factors on the growth of greening plants through measuring maximum photochemical efficiency(Fv/Fm)and withered and falling leaves ratio.The aim of this study was to determine the key factors for the coastal greening,obtain the first set of environmental database for the greening with heavy salt spray in the southern sandy coast,and provide reference for coastal greening.The main results were as follows:1.Obvious salt damage symptoms were observed in greening plants of Gulei,and varied with season.In autumn and winter,salt damage symptoms of greening plants were appeared in forms of leaves tips and margins withered or even etiolated leaves dropping,windward plants often appeared flag-shaped crown.2.Soil salt stress was not the cause of poor growth of greening plants.The average salt content of soil in this area was 0.3‰,far below 1‰,and the pH was range from 7.1 to 8.4.It concluded that the soil at Gulei was not the saline-alkali soil.3.The average annual salt spray deposition at distance of 100 m from the coastline was 98.4 mg/(m2 d),far higher than the average of 33.1 mg/(m2 d)in the southeastern coastal area,indicating that Gulei was a strong salt spray area.4.The results of study on the in:fluence of the distance from the coastline,the season,the wind speed,the wind direction,the protection of the shelterbelt and the height on the salt spray deposition showed that the deposition of salt spray deposition was significantly decreased with the increase of the distance from the coastline(P<0.05).From the coastline 100 m to 1700 m,salt spray deposition decreased by an average of 47.14%.The rule of salt spray deposition changed varies with the seasons was:summer<spring<autumn<winter.The dry deposition of salt spray increased with the increase of northeast wind frequency and average wind speed,and they coincided with the seasonal variation and reached the maximum in winter.The variation rule of northeast wind frequency was:spring<summer<autumn<winter,and reached up to 81.2%in winter.The variation rule of average wind speed was:summer<spring<autumn<winter.The shelterbelt on the side of the sea can significantly reduce the amount of salt spray deposition,and the reduction rate was 49.54%in winter(P<0.05).There was no significant difference in the effect of height on salt spray deposition(P>0.05).Through the analysis on principal components and redundancy analysis,the environmental factors which had the great influence on salt spray deposition were:distance from coastline,average wind speed and northeast wind direction frequency.5.Plant growth state was gradually improved as the distance from the coastline increased.The seasonal variation rule was:summer>spring>autumn>winter.6.Plant growth state became poor with salt spray deposition increased.Except Alstonia scholaris,there were significant correlations with the salt spray deposition and the plant growth state(r=0.85～0.99,n=5,P<0.05).The Fv/Fm values of Hibiscus chinensis leaves decreased with the increase of salt spray deposition,but there was significant difference only in winter(P<0.05).7.The key environmental factor of the poor growth of green plants at Gulei was salt spray deposition,and the plant growth state was closely related to salt spray deposition.8.The presence of shelterbelt can greatly reduce the harm of salt spray to coastal greening plants,which was more obvious in autumn and winter.In winter,under the protection of shelterbelts,the reduction rate of withered and falling leaves of trees was 40.0%～85.0%and the reduction rate of shrubs and herbs was 8.0%～35.7%,which indicated that the shelterbelts could make the plants grow well.Comparing trees with shrubs and herbs,the role of the promotion was more obvious to trees.The Fv/Fm values of Hibiscus tiliaceus,Ficus religiosa and Ficus altissima were significantly higher than those in unprotected forest road(P<0.05).9.Synthesized the degree of salt spray hazard,the distance from the coastline and the amount of salt spray deposition,the salt-tolerant ability of 10 species were as follows,trees:Hibiscus tiliaceus>Ficus altissima>Phoenix sylvestris>Erythrina ×sykesii>Ficus religiosa>Alstonia scholaris,shrubs and herbs:Fagraea ceilanica>Hibiscus rosa-sinensis>Duranta erecta>Catharanthus roseus.This study shows that Gulei is a strong salt spray area.The salt spray deposition is the main environmental factor that leads to the poor growth of local greening plants.The salt spray must be taken into account during greening in these coastal areas.Hence there is a need of screening and utilization of salt-tolerant plants,the construction of forests,the use of buildings,micro-landform,wind barriers,special planting and conservation measures to integrately research and develop coastal greening technology system in strong salt spray areas.