Study On The Morphological Plasticity Mechanism Of Leymus Mollis Grown In Coastal Dunes Of Different Far From The High Tide

Due to coastal beach long-term affacted by sea wind,tides and sea erosion,the beach sand is blown to the shore and piled up so that there is a big sand dune parallel to coast,which formed two sides,windward side faced to sea and leeward side back to sea.But environments of windward side and leeward side are very different in soil salinity,sea wind intensity,atmospheric humidity and other micro environments(i.e.,environmental heterogeneity).Leymus mollis is a dominant plant not only growing and forming a single population near by the high-tide line with high-salt and strong wind,but also growing on leeward side far from the high-tide line with low-salt and weak wind.But it is still unclear whether the regulation mechanism are involved in L.mollis adapting to heterogeneous environment,and what role of morphological plasticity of L.mollis are played in its adaptation to heterogeneous environment.In this study,the analysis in salinity and nutrient contents in the soil,in the changes of morphological characteristics such as plant height,leaf width,leaf length,root diameter and sprout characteristics,and in the changes in the distribution ratio of carbohydrate content in various organs in L.mollis grown in different far from the high tide line in different seasons were conducted in order to reveal the regulation mechanism of morphological plasticity in L.mollis adapting to the heterogeneous environment,to enrich the theoretical basis of plant wind-sand resistance and to provide theoretical basis for coastal environmental protection and restoration of introduced plants.The results were as follows:(1)There were significantly differences in soil salinity and soil nutrients in different set far from the high tide line along the coast.The seasonal changes in soil moisture,water-soluble salt ions(Na~+,K~+,Cl~-)and in soil nutrients(total nitrogen,available nitrogen,available potassium,total potassium,available phosphorus,total phosphorus,and soil organic matter)were determined from the rhizosphere soil of L.mollis grown on different far from the high tide line to reveal the differences of soil moisture,soil salt and nutrients in the environment of Leymus mollis.The results showed that the soil moisture content,Na~+,K~+and Cl~-content were the highest in the soil of near-high tide line(in 10m set),especially its Na~+content was higher by 28times than that in the soil far high tide line(in 70m set).But the contents of total nitrogen,available nitrogen,total potassium,available potassium,total phosphorus and available phosphorus in the soil far from high tidal line(70m)were higher by 32.9%,48.8%,30.0%,29.4%,10.1%,98.1%respectively than that in the soil near higher tide(10m).Soil available nutrients were negatively correlated with soil salt ion content.It indicated that coastal zone in 10m set near high tide had higher in soil salinity,stronger in sea breeze and lower temperature,while the the coastal zone far from the high tide line(in 70m set)had lower in soil salinity and soil moisture and sea breeze intensity,and higher in temperature and soil nutrients.It presented that excessive concentrations of soil salinity could inhibit the conversion efficiency of soil effective nutrients.There were differences in the morphological structures of L.mollis grown on different far from the high tide line of the coast in different seasons.The morphological characteristics,such as plant height,leaf width,leaf length,root diameter and sprout characteristics were analyzed in L.mollis grown on different far from the high tide line in fixed set and timing,so that to reveal the role and regulation mechanism of morphological plasticity were played in L.mollis adapting to heterogeneous environments.The results showed that there were significant differences in morphological characteristics between different far from the high tide line(P<0.05).In terms of leaf characteristics,the leaves of L.mollis at 10m from the high tide line were short and wide.With increasing of the distance from the high tide line,the leaves of L.mollis gradually became slender.The leaves of L.mollis at 70m from the high-tide line was the longest.For instance,the leaves lengths of L.mollis at 70m were longer by31.87%,35.14%and 5.94%than those at 10m,30m and 50m,respectively.In terms of root characteristics,the root diameter of the L.mollis was the largest at 10m(especially in spring and winter),and became smaller with increasing of the distance from the high tide line.Meanwhile,at 10m set the root spacing was larger and where were more new roots.With increasing of the distance from the high tide line,the root spacing became smaller and there were fewer new roots.In terms of bud characteristics,at 10m set,the new buds of L.mollis were longer,thicker and stronger,the deepest distributed in the soil(in autumn and winter),while at 70m set,the new buds of L.mollis were small and shallowly distributed in the soil.In terms of biomass partitioning,the L.mollis grown on the near high tide line(10m set)distributed more substances to the underground part.With increasing of the distance from the high tide line,L.mollis provided more substances to above-ground to accelerate branches and leaves growth.Due to the differences in the matter distribution strategy of L.mollis grown on different environments,there were differences in root-crown ratio of L.mollis among different set far from high tide.At 10m set,root-crown ratio of L.mollis was the smallest.With increasing distance far from the high tide line,the root-crown ratio of L.mollis became bigger.For instance,compared with 10m set,the root-crown ratio of L.mollis at 30m,50m and 70m set increased by 103.5%,78.5%and 58.2%,respectively.It indicated that L.mollis provided more substances to root organ to promote new roots growth,rhizomes growth and buds formation,which could not only increase L.mollis resistance to sea wind,and drought and salt,but also were beneficial to the formation of new shoots and accelerated the extension and growth under the sand.In contrast,with increasing distance far from the high tide line,air temperature and nutrients in the soil increased.At 70m set,L.mollis provided more substances to upgroude to acclerate leave growth,so that L.mollis at 70m was taller,shallower root system,smaller root diameter,and smaller a nd shallower buds.It presented that morphological characteristics of L.mollis in different sets far from the high tide line were changed significantly under the heterogeneous environment.(2)There were differences in the carbohydrate partitioning in different organs of L.mollis grown on the different sets far from the high tide line in different seasons.The contents of structural and non-structural carbohydrates in various organs of L.mollis grown on the different sets far from the high tide line were analyzed.The results showed that large amounts of carbohydrates were accumulated in underground part to maintain the regeneration of L.mollis in different far from the high tide line,but there were significant seasonal differences.In winter,L.mollis accumulated a large amount of carbohydrates in new roots and buds to improved their frost resistance and enabled the L.mollis to overwintering safely.In summer,the carbohydrate of L.mollis was mainly distributed to the new and old roots,and the higher in the cellulose content of the rhizome and leaf.It showed that it was the key to maintain higher cellulose contents in the rhizome and leaves of L.mollis in increasing its resistance to freezing and wind.However,the higher contents of cellulose in the new buds could ensure that the new buds moved through the sand to expand their population.The ratio of carbohydrate partitioning was higher in the underground organs of L.mollis grown near the high tide line than that in the set far away from the high tide line.Therefore,L.mollis grown different sets far from the high tide line had stronger in physiological plasticity of carbohydrate partitioning,which played an important role in the formation of morphological plasticity,in its keeping on a wide ecological range,and increasing resistant abilities to adapt to heterogeneous environment,In short,L.mollis grown in different sets far from the high tide line can adapt to environmental heterogeneity of coastal dune by adjusting the morphological plasticity and carbohydrates partitioning in various organs.It can make conclusion that the morphological plasticity and carbohydrates partitioning played an important role in increasing resisitance of L.mollis to salinity,sea winds,drought,high temperature,and adapting to environmental heterogeneity.