Study On Response Of Firmiana Platanifolia Seedling Growth And Physiological And Biochemical Characteristics To Water Stress

Firmiana platanifolia is widely planted as the City Tree of Chaohu City,Anhui Province.In this study,one-year-old container seedling of Firmiana platanifolia was taken as the object to explore the effect by water stress.We designed 4 different water conditions such as 30%field capacity（T1）,70%field capacity（T2）,100%field capacity（T3）and 130%field capacity（T4）under.The paper analysed the index such as growth characteristics,（growth state of health,plant height,stem diameter,leaf area,etc.）,biomass allocation features（leaf biomass,stem biomass ratio,root biomass ratio）,physiological and biochemical characteristics（chlorophyll a,chlorophyll b,net photosynthetic rate,transpiration rate,intercellular CO₂ concentration,stomatal conductance,vapor pressure deficit）and non-structural carbohydrates（soluble sugar,soluble lake,etc.）.It provided a scientific basis for the selection of water conditions for seedling cultivation under different water stress degrees.The main research results were as follows:（1）In the range of T2～T3 field water capacity,the health of Firmiana platanifolia Seedlings is relatively good.Under T1 and T4 field water capacity conditions,the stress time was about 10 days,and the health status of seedlings began to deteriorate significantly;After 20 days of stress,the health status of Firmiana platanifolia Seedlings ranked from excellent to good,T2 field capacity>T3 field capacity>T1 field capacity>T4 field capacity.When the stress time was 20 days,the seedlings in T1 field were in the worst health state under the condition of water holding capacity.The leaves were dark green,the epidermis shrank seriously,the leaves wilted and drooped obviously,the leaves were infected with water stains,the black spots on the bark deepened,and the number of aerial roots increased.Therefore,it can be seen that the arid soil water condition is more unfavorable to the growth and health of Firmiana platanifolia Seedlings than the flooded water soil condition.（2）The change trend of growth index of Firmiana platanifolia Seedlings under T2water condition was the best.Under T2 water condition,the changes of plant height,stem diameter,leaf width,leaf length and leaf area increased with the increase of stress days.After 20 days of stress,the leaf area index was significantly higher than（P<0.05）the other three water conditions,increase of 56.9%compared with 0 days;Under T1 water condition,with the increase of water stress time,the change of stem diameter in 20 days decreased by 13%compared with 0 days;Under T3 water condition,the change of stem diameter was the largest in 20 days,increased by 92%compared with 0 days,and the number of leaves was up to 7 pieces/plant;Under T4 water condition,the growth indexes of Firmiana platanifolia Seedlings increased continuously with the increase of water stress time to 15 days,and the growth indexes decreased after 15 days,and the leaf area and leaf length indexes of 20 days were significantly lower than（P<0.05）0 days.Therefore,it can be seen that T2 water condition is more conducive to the growth and development of Firmiana platanifolia Seedlings.When the seedlings are under drought stress T1,it has a great impact on the seedling height and stem diameter,and the growth index decreases with the increase of stress time;When the seedlings were in T3 condition with wet soil,they had significant positive effects on plant height,stem diameter and leaf number;When the seedlings were under water flooding stress T4,the width of seedling leaves increased significantly,but all growth indexes showed a downward trend after 15days of stress..（3）The biomass distribution of Firmiana platanifolia Seedlings under T2～T3 water condition is most suitable for the growth and development of seedlings.After 20 days of stress,the leaf biomass allocation ratio（LBR）of Firmiana platanifolia Seedlings under T1 and T4 water conditions was significantly lower than that under the other two water conditions（P<0.05）;Under T4 water condition,the stem biomass distribution ratio（TBR）of Firmiana platanifolia Seedlings was significantly higher than（P<0.05）the other three water conditions;Under T1 water condition,the root biomass distribution ratio（RBR）of Firmiana platanifolia Seedlings was significantly higher than（P<0.05）the other three water conditions.It can be seen that the seedlings of Firmiana platanifolia will increase the volume of root system and improve the water absorption efficiency of root system by increasing the distribution of root biomass after being subjected to drought stress and T1water condition.At the same time,it will also reduce the distribution of leaf biomass,reduce leaf area and reduce the evaporation of leaf water;Under the T4 water condition of flooding stress,Firmiana platanifolia Seedlings will increase the biomass distribution at the stem base to achieve the effect of gas rooting and improve the gas exchange capacity of the tree,but at the same time,it will limit the growth of seedling leaves and reduce the biomass distribution of leaves;Under suitable water conditions（T2 and T3）,the distribution of leaf biomass of Firmiana platanifolia Seedlings will increase significantly,which will promote plant photosynthesis and increase the carbon accumulation of plant components.（4）The photosynthesis efficiency of Firmiana platanifolia Seedlings under T2～T3water conditions was the highest.The changes of chlorophyll a and chlorophyll b indexes can also reflect the sensitivity to water stress.The experimental results show that the contents of total chlorophyll,chlorophyll a,chlorophyll b and chlorophyll a/B in the leaves of Firmiana platanifolia Seedlings under drought stress T1 water condition and flooding stress T4 water condition change significantly,It can be further reflected that Firmiana platanifolia is a tree species sensitive to the water conditions of the growth site conditions.Drought stress T1 water condition and flooding stress T4 water condition all affected the leaf photosynthesis,chlorophyll index,water effective utilization index（WUE）and steam pressure deficit index（VPD）of Firmiana platanifolia Seedlings,which was largely caused by the restriction of photosynthesis due to the closure of stomata;The inflection point of intercellular CO₂ concentration in the leaves of Firmiana platanifolia Seedlings generally appears when the stomatal conductance is about 50(mol·m^-2·s^-1),that is,when the stomatal conductance is less than 50(mol·m^-2·s^-1),the values of net photosynthetic rate and transpiration rate will decrease sharply,while the intercellular CO₂ concentration will increase.（5）The content of non structural carbohydrates in the leaves of Firmiana platanifolia Seedlings under T2 water condition is the highest,that is,the content of nutrients in the leaves is the highest.After 20 days of stress,the contents of soluble sugar and starch in T1 water condition were the lowest and significantly lower than those in the other three water conditions（P<0.05）;It can be seen that when more water and sugar are transported to the stem of Firmiana platanifolia,the content of soluble matter in the stem and leaves of Firmiana platanifolia will increase,and the content of T2 nutrition will increase;Under T4 water condition,the content of soluble sugar and starch in seedling leaves decreased with the increase of stress time,which may be that sufficient water conditions promoted the photosynthesis of seedlings in the early stage of flooding stress.However,with the increase of stress time,higher soil water affected root respiration,and Firmiana platanifolia Seedlings adjusted their growth morphology,distributed nutrients to the stem base to produce aerial rooting.It can be seen that appropriate water conditions help to significantly increase the non structural carbohydrates in the leaves of Firmiana platanifolia Seedlings,so as to ensure that the nutrients in the seedlings are sufficient,so that Firmiana platanifolia seedlings can resist the impact of abiotic stress and survive the winter safely.