Study On Adaptability In Needle Traits Of Pinus Thunbergii Along Coastal-inland Gradient

The intensity and frequency of the wind stress along coastal-inland gradient show the characteristics of spatio-temporal variation.With the increase of the distance from the coast,the wind speed gradually decreases,thus forming different degrees of wind-stressed habitats.The wind affect trees traits mainly by changing the atmosphere around trees and enhance mechanical stimulation,especially leaf functional characters,thus causing blade to produce“thigmomorphogenesis”.There have been a lot of control experiments concerned effect of wind on plants in the early stage,but they seem still insufficient on the long-term studies under natural wind condition.Therefore,in recent years,the research on the response and adaptation of tree species to wind stress has been concerned by many scholars.It is important to study the survival strategy and physiological regulation mechanism of trees in windy environment for deep understanding of physiological and ecology of plant in adversed environment,it also plays an important guiding role in the construction and operation of coastal protection forest.In this study,there are three sampling lines every 700 m vertical to coastline in the eastern coastal area of northern China.Eight pure sampling forest of the same age of P.thunbergii are selected from each sample line every 100 m,and 24 plots are set up.Samples of soil and P.thunbergii needle were collected on the upwind and leeward sides of P.thunbergii respectively to analyze the morphological,anatomical and structural characters,stoichiometric characters,carbohydrate content and distribution of the needles on the coastal gradient to explore the relationship between needle traits.The results show that:1.Variation in needle morphology and anatomy of P.thunbergii along coastal-inland gradientThe length,width,perimeter,area,thickness and specific leaf area of the of P.thunbergii needle on windward side on the coastal gradient are gradually decreased with the decrease of the distance from the coast(P < 0.05);while the cuticle thickness,epidermal thickness and vessel diameter are gradually increased with the decrease of distance from the coast(P<0.05),and there was no obvious change of each index on leeward side.The needle characters on upwind and leeward side(except specific leaf area)of P.thunbergii were significantly different within 500 m far from coastal area(P < 0.05).Therefore,with the increasing of sea wind stress,needle morphological indices decreased to reduce the force bearing area,meanwhile,needle anatomical indices increased to improve needle toughness,which showed the response and adaption strategies in coastal wind environment for P.thunbergii.2.Variation in needle stoichiometric characters of P.thunbergii along coastal-inland gradientCoastal gradient,the leaf stoichiometry on windward side(except organic carbon),exchangeable calcium and sodium content of needles on leeward side gradually increased with distance decreased from the coast;characteristics above tends stable when distance is more than 400 m from coastal,differences of all element contents in needles on the windward and leeward side is significant mainly when distance from coastal is less than 400m(P < 0.05);There is a significant correlation of leaf stoichiometry among the windward sides(except magnesium and potassium,organic carbon and total phosphorus,total phosphorus and potassium,total phosphorus and magnesium);on the leeward side only total nitrogen and phosphorus,calcium and sodium are significantly correlated(P < 0.05);the variation of stoichiometry characters of needles on windward side are largely determined by wind stress and soil nutrient content(except for N:P ratio),explanation of wind stress is 77.15%-97.23%.In sum,the needle chemical element contents of P.thunbergii were significantly changed by wind stress,but the ratio is relatively stable,with the increasing of sea wind stress,the needle carbon assimilation function was significantly affected;Meanwhile,needle nitrogen,phosphorus,potassium,calcium,sodium and magnesium contents increased to improve tolerance,which is a kind of tolerance strategy.These results showed the response and adaption strategies in coastal wind environment for P.thunbergii.3.Variation in needle carbohydrate content of P.thunbergii along coastal-inland gradientThe nonstructural carbohydrate content of P.thunbergii on the coastal gradient on windward side decreases with the decrease of the distance from the coast;soluble sugar:starchratio,structural carbohydrate content,lignin:cellulose ratio gradually increase with the decrease of distance from the coast;characteristics above tends stable when distance is more than 400 m from coastal;but the difference of indicators on leeward side in the gradient is not significant.Significant differences of needle leaf indexes of P.thunbergii between windward and leeward sides mainly exist within 200 m far from coastal area.Therefore,with the increasing of sea wind stress,non-structural carbohydrates,starch and cellulose was gradually transformed into structural carbohydrate,soluble sugar and lignin,to increase the flexural capacity and the water retention.4.The correlation between stoichiometric characters and carbohydrates of P.thunbergii along coastal-inland gradientAlong the coastal-inland gradient,a significant positive correlation exists between structural carbohydrate and calcium content(P < 0.05);a significant negative correlation exists between the non-structural carbohydrate content and nitrogen content in windward needle of P.thunbergii(P < 0.05);no correlation exists among variables on leeward side(P > 0.05);the soluble sugar:starch ratio is significantly positively correlated with calcium and phosphorus content,while on leeward side,the soluble sugar:starch ratio is significantly negatively correlated only with calcium content and no correlation with phosphorus content.The results showed that the transformation of carbohydrates in windy environment is closely related to the stoichiometric characteristics.5.The correlation between chemical characters and morphological anatomy features of P.thunbergii along coastal-inland gradientOn the windward needle,correlation exists generally among stoichiometric characters,carbohydrate content,components distribution and morphological characteristics,among which the organic carbon content and the non-structural carbohydrate content are positively correlated with the morphological characteristics;Nitrogen,phosphorus,potassium,calcium,sodium,magnesium,soluble sugar:starch ratio and structural carbohydrate content are negatively correlated with morphological characteristics;A significant positive correlation exists between SLA,epidermal thickness and cellulose:lignin ratio,lignin:cellulose ratio(P<0.05),almost nocorrelation was found among the indicators on leeward side.Therefore,the chemical characters in needle of P.thunbergii in the windy environment have important regulatory effects on the morphogenesis.