Effects Of Different Irrigation Methods On Mitigation Salt Spray Damage Of Coastal Greening Plants

As there is plenty of rainfall in southern China,the soil leaching on sandy coasts is strong,and the soil salt stress is weaker than that in northern areas.The factor that limits the growth and development of vegetation growth on the first-line coastal is mainly attributed to the salt in the air,salt spray.As people are not concerned with the salt spray stress,the vegetation restoration in the southern coastal areas mostly focuses on preventing and controlling the damage caused salt in the soil,which leads to a variety of common problems such as high greening costs,vegetation coverage reduction,low survival rate,and single form of greening.Currently,most studies on the salt spray focus on screening salt-spray-tolerant plants,but planting salt-fog-tolerant plants can not completely meet the needs of greening in areas with strong salt spray settlement,and certain strong salt spray settlement weather still causes fatal damages to plants.Therefore,there is an urgent need to formulate appropriate management and protection plans in subsequent periods to avoid or minimize the damage caused by the salt spray.In this research,two common tree species Nerium oleander and Casuarina equisetifolia for coastal vegetation restoration in the south have been chosen,six irrigation methods were used under salt-free spray stress,low salt spray stress and high salt spray stress,such as root irrigation with more tap water,sprinkling irrigation with more tap water,sprinkling irrigation with less tap water,root irrigation with more brackish water,sprinkling irrigation with more brackish water,and sprinkling irrigation with less brackish water.Its three types of indicators have been measured,such as physiological(K+,Na+,Ca2+,Mg2+,Cl-,total Chlorophyll content and relative water content),morphological(basal diameter,? Height and crown width)and visual evaluations(buds damage and healthy leaf quantity)to assess its mitigation effect on salt spray stress in order to find the best irrigation method.At the same time,the three variables,water quality,water quantity and water supply method have been analyzed for explanation so as to determine the most important variable to alleviate the salt spray stress and provide priority to the subsequent management and protection,with the main results as follows:Without salt spray stress,water quality plays a major role in plant growth.The use of irrigation with brackish water will result in a decrease in K+/Na+ and an increase in Cl-content(p<0.05),but there is no significant difference between various treatments(p>0.05).The contents of Ca2+and Mg2+ are relatively stable and they do not form ion stress or ion loss.The growth rate of seedling height growth quantity and crown width of the corresponding plant is slower than that with tap water irrigation(p>0.05).Plants that have been sprinkled with brackish water with 5 ‰ salinity in the long term showed a certain degree of decline in green leaf retention.Therefore,in the case where landscape effect requirement is not so high and environmental conditions are limited,it is advisable to use brackish water for root irrigation.If it is necessary to use sprinkling irrigation,the salt in the water should be minimized and constant tracking should be maintained.As compared with the case that is free from salt spray stress,under the conditions of salt spray stress,the influence of water quality has gradually weakened without significant difference between tap water and brackish water(p>0.05).Conversely water supply method has a relatively big influence on alleviating plant salt spray stress(p<0.05),to which priority should be given in satisfying.As compared with root irrigation,the change difference in ion contents and base diameters is insignificant in sprinkling irrigation(p>0.05).However,on one hand,the use of sprinkling irrigation can maintain higher chlorophyll content and relative water content from the physiological perspective(p<0.05);on the other hand,the use of sprinkling irrigation speeds up growth(? Height)and the leaves are relatively healthy under the low salt spray stress from the morphological perspective(low buds damage and high healthy leaf quantity).By comparison of the indicators of oleander and casuarina in different treatments,it has been found that casuarina is more resistant to salt spray than oleander,with a better alleviation effect of sprinkling irrigation.Besides the abnormal leaves that the casuarina congenitally has,the reason may also lie in the fact that casuarina has a salt gland that can discharge excessive salt in time and take away the salt in time through sprinkling irrigation.In summary,through comparison of the change trends of K+/Na+ and Cl-of plants under different stress extents,it is possible to find that K+/Na+ of all treatment groups with different water qualities,water quantities and water supply methods showed a downward trend while Cl-showed an upward trend.The extent of this trend that decreases or increases with the escalation of salt spray stress became bigger,showing that the effect of irrigation on alleviating plant salt spray stress is limited.Irrigation can only prevent the accumulation of salt on plant leaves in the long term,but cannot prevent the salt from settling down on the surfaces of plant leaves.Therefore,irrigation(no matter root irrigation or sprinkling irrigation)can only play a certain supporting role,and cannot fundamentally prevent the salt spray from damaging plants.In coastal greening project practice,it is necessary to intensify the assessment of salt spray hazards and the monitoring of the salt spray settlement,and adopt the management and protection strategy that focuses on prevention and control with irrigation as the auxiliary means.In areas where salt spray is more serious,it is necessary to intensify the construction of wind barriers and windbreak forests to minimize the salt spray settlement on plant surfaces.In areas with scare water resources,root irrigation can be conducted directly under the monitoring of the salt in unconventional water resources.In areas with strong salt spray settlement and adverse weather,sprinkling irrigation measures such as on-tree sprinkling irrigation should be established to help plants wash out salt.In terms of water quantity,it is proper to drip water on leaf surfaces,and its frequency needs to be flexibly regulated according to the extent of the salt spray damage so as to prevent excessive salt settlement on the plant leaves.