Study On Drought And Saline-alkaline Resistance Of Scaevola Sericea

Scaevola sericea(Goodeniaceae),a perennial evergreen shrub or small tree,common in tropical coastal area,is the dominant plant species in the coral vegetation of the Paracel Islands.S.sericea shows strong adaptability to coral reef environment such as drought,salinity and barrenness,and plays an important role in windbreak,sand fixation and vegetation restoration of islands and coastal zone.However,there is still a lack of research on the mechanism of drought and salinity tolerance of S.sericea,which limits the development and utilization of this species.In this study,the drought and saline-alkali environment of coral islands was simulated artificially,and conducted a controlled experiment involving different levels of drought and saline-alkali stress treatments to assess the growth,morphological and physiological responses of S.sericea.The objective of this study was to explore the mechanism on physiological and ecological adaption of S.sericea to drought and saline-alkali soil condition,as to provide theoretical basis for the introduction,cultivation,development and utilization of S.sericea.The main results are as follows:(1)With the increase of drought degree,the growth of S.sericea decreased,and the antioxidant enzyme activity,content of soluble sugar,soluble protein and proline of the leaves decreased.Under the drought stress,the activity of antioxidant enzymes of S.sericea will increased to eliminated a large number of active oxygen produced by drought stress;Meanwhile,its content of osmotic adjustment substances such as soluble sugar,soluble protein and proline will increased to reduced cell osmotic potential,which is beneficial to the water absorption.The content of abscisic acid increased to regulated cell metabolism and other ways to resist the damage of drought stress.Under each treatment level,the ascending-declining-increasing trend with increasing treatment time was found for the antioxidant enzymes activity and soluble sugar and proline content of S.sericea.This indicated that S.sericea can respond to drought stress rapidly and adapt to short-term and low-level drought stress.S.sericea had great resistance to drought and is well tolerant and adaptable to transient and low-level drought stress,but the growth was significantly inhibited or even caused death under high-level drought stress(soil water content less than20%).We suggested that during the planting and maintenance process,the soil water content of S.sericea should be kept above 25%,and the longest irrigation period is 14 d.When the soil water content is less than 20%,the longest irrigation period is 7d.(2)With the increasing degree of saline-alkali stress,the growth of S.sericea generally showed a downward trend,but low saline-alkali stress promoted the growth of S.sericea to some extent.With the increasing degree of saline-alkali stress,the antioxidant enzyme activities,the soluble sugar,soluble protein and proline contents of S.sericea showed a downward trend.Under all the saline-alkali stress treatments,we found increased in the antioxidant enzymes activities of S.sericea,and in its content of osmotic adjustment substances(e.g.soluble sugar,soluble protein,proline and abscisic acid)to eliminated active oxygen and reduce osmotic potential of S.sericea to resist saline-alkali stress.With increasing treatment time,the antioxidant enzymes activities and abscisic acid content of S.sericea showed a rising-decreasing-increasing trend,indicating its adaptation to short-term and low-concentration saline-alkali stress.The content of osmotic adjustment substances of S.sericea showed a trend of decline after increasing with increasing of the treatment time,which might due to the cell damage of S.sericea caused by high-level saline-alkali stress,which hindered its partial synthesis of osmotic adjustment substances.S.sericea has great resistance to saline-alkali stress,and its response to saline-alkali stress was “low-promotion and high-inhibition”.The low-concentration saline-alkali stress(salt concentration below0.5%,pH 7.5~9.1)will promote the growth of S.sericea to a certain extent,while the high-concentration of saline-alkali stress will significantly inhibit its growth and even caused death.The tolerance threshold of S.sericea to saline-alkali stress was 1.94% for salinity and 10.7 for pH.During the planting and maintenance,we suggested to construct moderate saline-alkali environment promote the growth of S.sericea.When the degree of environmental saline-alkali is high(salinity >1.94%,pH >10.7),appropriate substrate improvement measures(such as adding acid modifier,dripping water to remove salt,etc.)should be taken to ensure the normal growth and survival of S.sericea.