The Main Problem Of Vegetation Restoration In The Coastal Areas Of South China-Salt Spray Injury

The natural environment in the southern coastal areas of China is terrible,such as high temperature,drought,wind,blow sand,poor soils and heavy salt spray and so on,which are very prominent in these areas.It leads the plant restoration work in the southern coastal areas to be difficult,especially the coast areas effected by the strong waves,where the survival rate and the growth score of plants are low.In many places,like Zhoushan Islands of Zhejiang,Pingtan,Chongwu,Shishi,Xiangzhi and Dongshan of Fujian,Nanao of Guangdong,Wenchang Moon Bay of Hainan,Penghu,Gaoxiong and Kending of Taiwan,the coastal plants have shown obvious salt injury symptoms.However,the symptoms of salt injury of these plants are different with that caused by soil salt injury.In addition to the new born leaves and buds are the first to be hit,the salt injury in the windward side tend to be more serious than the leeward side and with great seasonal differences.Therefore,we speculated that the main cause of plant salt injury in the southern coastal areas may not be the soil salt,but other reasons.In this study,a field survey of 24 sites were carried out in the southern coastal areas,including Zhejiang,Fujian,Guangdong,Guangxi,Hainan and Taiwan provinces,which is divided into the rainy(from May to September)and dry season(from November to March).In this paper,according to the assessment of the greening plants growth and the analysis of soil factors,combined with the collection and research of meteorological data,we aim to explore the true cause of plant salt injury and find the difficulties in plant restoration in the southern coastal areas,and to provide a reference for the coastal greening work.The main results are as follows:1.The soil salinity of most native sites was on a quite low level,mainly varying from 0.197‰ to 0.776‰,belonging to desalted soil(<1‰).The proportion of rainy season and dry season was up to 91.7%and 85.4%respectively,whereas some places belonged to light salt soil(1‰?4‰)and only Penghu's surface soil in the dry season belonged to salt soil(4‰?-6‰).The soil pH,salinity,exchangeable Na+ and salt saturation percentage of the surface soil was higher than the middle soil(20-40 cm)and that the dry season was higher than the rainy season,among which the soil saturation in the rainy and the dry season was 83.3%and 62.5%respectively.It did not conform with the normal leaching rule,and the returned salt base phenomenon was obvious,especially the most serious spray splash areas.2.The salt injury level of plants had a significant positive correlation with the salinity of surface soil and the salt saturation percentage of middle soil(P<0.05),the correlation coefficient were 0.4281 and 0.4634 respectively.And there was a extremely significant positive correlation between the salt injury level of plants and the wind speed(P<0.01).The correlation coefficient between the average annual wind speed and the salt injury level of plants in the rainy and dry season were 0.8465(P<0.0001,24sites)and 0.6591(P=0.0005,12sites)respectively.While the correlation coefficient between the salt injury level of plants in the rainy and the dry season with the average wind speed of the same period were 0.8047(P=0.011)and 0.8349(P=0.003)respectively.3.Based on the above results,we concluded that the main cause of plant salt injury in the southern coastal areas was the salt in the air(salt spray).The salt injury level of plants was highly related to the wind speed.The salt carried by wind was the major factor threatening plant growth.As the carrier of the salt spray,the higher the wind speed was,the more severe the salt spray injury was.In addition,the tropical storm surge would aggravate the salt injury to coastal plants.4.According to the symptoms of salt spray injury and the physicochemical properties of soil,as well as the meteorological data,the first map was drawn to reflect the different degrees of plant salt injury across the coastal areas of South China.The map indicated that the plant salt injury in the southern coastal areas of China are common,especially in most coastal areas of Fujian province,such as Pingtan,Meizhou Island,Chongwu,Xiangzhi,Shenhuwan,Gulei and Dongshan,close to the Taiwan Strait.Meanwhile,the west coast of Penghu Island and the northern coast of Fuguijiao,Taipei in Taiwan province belong to the heavy salt injury areas,basically up to 4 or 5 salt injury level.Secondly,due to tropical storm surges,salt injury at most areas in Guangdong Province and some coastal areas of Zhejiang and Hainan are serious.For example,the coasts of Guangdong Province could reach almost 3 level and more.They belong to strong salt injury or heavy salt injury areas.Therefore,the coastal plant restoration and coastal greening work in the strong and heavy salt injury areas should be paid special attention to salt spray injury.5.Considering the lack of relevant theories and techniques of plant salt spray injury and the prevention of salt spray injury,we took the coastal road greening at Gulei as an example and put forward one diagnostic method for coastal landscape plants of salt spray injury.A set of measures on salt spray prevention suitable for the southern coastal areas were proposed,with respect to selection and arrangement of salt spray-tolerant plants,construction of shelter belts,the selection of planting time,types of construction tools such as wind barrier and salt spray network,later conservation technology,seedling breeding technology research and breeding base construction.And these could provide a reference for the garden greening workers.