| The bark of Betula platyphylla is white,the trunk is straight,the tree shape is beautiful,and it has a high ornamental value,It is widely used in gardens.However,the survival rate of Betula platyphylla in Shenyang and south of Shenyang is low(40 % or less)and the growth is poor.The reason for this may be caused by the arid and hot summer weather in Shenyang and the high temperature in summer,which is caused by the obvious difference between the cold and cool climate of the natural distribution area of Betula platyphylla.Through scientific and technical means,this paper explores the causes of incompatibility between Betula platyphylla and environment,in order to provide theoretical and technical support for growth observation and cultivation management of Betula platyphylla.In this paper,Betula platyphylla was used as the material,treated with high temperature,high light,high temperature and high light,and thephotosynthetic characteristics and chlorophyll fluorescence parameters were measured.Combined with the indicators of temperature,solar radiation and rainfall,the changes of various indexes of Betula platyphylla under certain environmental conditions were analyzed,and the constraints of planting Betula platyphylla in Shenyang were explored.The conclusions were as follows:1.Under the conditions of appropriate temperature and solar radiation,moderate drought(soil water content is 0.16~0.21 m3/m3)stress can lead to a significant decrease in photosynthesis of Betula platyphylla.The initial decline points of transpiration rate(Tr),net photosynthetic rate(Pn)and stomatal conductance(Gs)of Betula platyphylla were 1.91 mmol·m-2·s-1,4.78 ?mol·m-2·s-1,65.96mmol·m-2·s-1,respectively.mmol·m-2·s-1,26.78 mg/l,the corresponding soil water contents were 0.17 m3/m3,0.21 m3/m3,0.16 m3/m3,and 0.16 m3/m3,respectively.2.Under different drought stress conditions,extreme high temperature,or extreme solar radiation,or high temperature and solar radiation synergistic stress can cause damage to the Betula platyphylla photosynthetic system.(1)under mild(0.21~0.25m3/m3)drought stress,when the air temperature is higher than 35 ?,and the solar radiation is higher than 820 w·m-2;Or when the air temperature was higher than 38 ?,the PSII reaction center in Betula platyphylla leaves was irreversibly inactivated.(2)under moderate(0.16~0.21m3/m3)drought stress,when the air temperature is higher than 33 and the solar radiation is higher than 820 ?w·m-2.Or when the air temperature is higher than 35 ?;Or when the solar radiation is higher than 850 w·m-2,the PSII reaction center in Betula platyphylla leaves will be irreversibly inactivated.(3)under severe drought stress(0.10~0.16 m3/m3),when the air temperature is higher than 31 and the solar radiation is higher than 750 w·m?-2,Betula platyphylla can be exposed to the water.Or when the solar radiation is higher than 800 w·m-2;Or when the air temperature was higher than 33 ?,the PSII reaction center in Betula platyphylla leaves was irreversibly inactivated.3.In the 2018 Shenyang area,30 days of Betula platyphylla may be exposed to high temperature stress(Duration155.5 h),66 d of Betula platyphylla may be subjected to strong light stress(Duration111.5 h),and 40 d of Betula platyphylla may be exposed to high temperature and high light synergistic stress(Duration 75.5 h).Insufficient precipitation in April-June,it is very likely to cause different degrees of drought stress.In the growth and development process of Betula platyphylla,if subjected to extreme environmental conditions,Betula platyphylla will have symptoms of growth and degeneration,damage to the photosynthetic system,and severe burns,wilting,and falling leaves.If Betula platyphylla is cultivated in shenyang area,water management should be strengthened. |
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