Effects Of Water And Salt Stress On The Growth And Physi-biological Characteristics Of Canavalia Maritima Seedlings

Canavalia maritima is widely distributed on coastal dunes or beaches in China,with good salinity and barrenness tolerance,and is known as an "ideal species" for coastal sand ecological restoration projects.However,due to the special habitat,C.maritima has been facing different degrees of water and salt stress for a long time,which affects the growth and development of C.maritima.At present,domestic and foreign research on water and salt stress in C.maritima is still insufficient,which limits its development and utilization in coastal ecological restoration work.Therefore,it is important to study the effects of environmental changes in water and salinity factors on the growth of C.maritima,and make scientific theoretical basis for its wider promotion and utilization for the coastal sand ecological restoration project.In this paper,we used C.maritima seedlings as the test material and set up three kinds of tests,namely salt stress,water stress and water-salt interaction stress,to study the growth and physiological characteristics of C.maritima seedlings in response to water and salt stress by measuring and comparing the effects of different levels of water and salt stress on the growth indexes,physiological indexes and anatomical structures of C.maritima seedlings,and then explore their growth and development patterns and adaptation mechanisms under water and salt stress.The results of the study were as follows.(1)Salt stress had an inhibitory effect on the growth of C.maritima seedlings,and the inhibitory effect was obvious when the salt stress exceeded 900 mmol/L.Water stress had an inhibitory effect on the growth of stems and leaves of C.maritima seedlings,while it promoted the root growth to a certain extent;the growth of C.maritima seedlings was severely inhibited under the interactive stress of water and salt stress,but they had a better ability to adapt to mild salt and waterlogging stress.(2)Under water and salt stress,the chlorophyll content of C.maritima seedlings fluctuated with the duration of stress,mainly due to changes in chlorophyll a content,and the overall chlorophyll a/b ratio remained stable;CAT,POD,SOD activity and MDA content all increased,and MDA content increased with the prolongation of stress,and the SOD and CAT activities of C.maritima leaves changed under salt and water stress Under stress conditions,the osmoregulatory response of C.maritima was sensitive,and the content of free proline and soluble sugar was rapidly increased at the beginning of stress to regulate the osmotic pressure balance,and when the salt content was higher than900 mmol/L or the water content was lower than 40%,the content of osmoregulatory substances changed drastically,and the protective effect of osmoregulation was significant;salt stress,water-salt The inhibition of photosynthesis of C.maritima under salt stress and water-salt interaction stress increased with the prolongation of stress time,while it was less affected by the stress time under water single stress.The interaction between light salt(300mmol/L)and water stress had little effect on chlorophyll fluorescence parameters,and the primary light energy conversion efficiency,potential PSII activity,and photosynthetic electron transfer efficiency of C.maritima seedlings were maintained at low levels of normal physiological activity.(3)The root,stem and leaf anatomical structures of C.maritima seedlings were altered under water and salt stress.Different degrees of salt stress promoted the widening of leaf fenestrations and showed an inhibitory effect on the thickening of spongy tissues.The proportion of water transport and storage tissues increased in stems under water or salt mono-stress,mainly by enhancing water storage mechanisms and altering transport efficiency to balance the contradiction between growth water demand and environmental water deficit.C.maritima roots were responsive to changes in soil water and salt content,and a certain level of stress treatment was beneficial to the growth and development of C.maritima roots,while it showed inhibitory effects when the limit of medium salt stress(900mmol/L)or severe drought(20%)was exceeded.(4)The results of correlation analysis showed that the development of transport tissues of C.maritima stems under water and salt stress was closely related to the growth differentiation of roots and leaves,and were closely related to each other.The results of principal component analysis showed that the three major morphological and physiological functions of osmoregulation,antioxidant enzyme system and conductive tissue were more responsive to water and salt stress,among which morphological adaptation and antioxidant enzyme system played a prominent role and were key to the adaptation ability of C.maritima seedlings to water and salt stress,and the related biomass,root volume and MDA content could be used as indicators of water and salt tolerance of C.maritima seedlings.Using seedling height as an indicator,the tolerance threshold model calculation determined that C.maritima has a strong salt tolerance threshold of548.67 mmol/L and a drought tolerance threshold of 23.44%.In summary,C.maritima seedlings tolerated mild salt stress and mild to moderate drought as well as waterlogging stress well,and were able to grow in an environment with salt content below 548.67 mmol/L or water content above23.44%,with strong tolerance,and were able to adapt to the harsh water and salt environment of coastal sandy areas,and could be used as pioneer plants for coastal restoration ecological projects at the frontier of coastal sandy areas.