The Research On The Eco-Physiological Characteristics Of Drought Endurance Of Pinus Sylvestris Var.mongolica

The eco-physiological characteristics of drought endurance of Pinus sylvestris var.mongolica were studied under different climatic regions, soil water and leaf water condition.Furthemore,the response and adaptability of trees to water stress was done.The below showed the results. 1 The parameters of drought endurance of P. sylvestris var. mongolica was measure and studied by PV technology in the subhumid, semiarid and arid regions The results indicated the osmotic potentials at water saturation condition (πo) and at the initial loss turgor(πp) decreased as the climatic drought degree increased,and related linearly with the climatic moisture index(Im).It was proved that the drought endurance of P. sylvetris var. mongolica was varible and the elevation of the osmotic adjust capability was a main way to the adaptation of trees to the drought climatic environment. 2 The relationship between the daily average(y) of the net photosynthetic rate, transpiration rate and water use efficiency tested trees and soil moisture content(x) or morning leaf water potential(x) could be expressed as y=a+be-kx. The soil moisture content(SWCp0)and the leaf water potential when the net photosynthetic rate equal to 0 were the indexs of the initial water stress condition for the growth and development of trees. SWCp0 could be used to evaluate the drought endurance of the tree species under the same soil and the order of the drought endurance of the tested trees was Platycladus orientalis>P. sylvestris var. mongolica>P. tabulaeformis>Picea meyeri. 3 The research on the relationship between the water absorption characteristic of the tested trees and the leaf water potential(ψ) showed that resaturation relative water content (RWCrs) could be a index to evaluate the water absorbing capability of trees. The water absorbing capability of trees was less when RWCrs was less. RWCrs decreased asψdecreased, the relationship between them was y=k-ae(bx).The relationship between the photosynthetic rate and the leaf water potential could be expressed as y=a+b/(1+e(-kx)). The correlative curve between the total photosynthetic rate, transpiration rate, fluorescence characteristic index and water potential was all "S" curve. 4 Based on the critical point of the above correlative curve of tested trees,results indicated πp was the minimal water potential for normal growth and development of trees as πp was the water potential at the initial variation of the absorbing characteristics,the the minimal water potential of the transpiration rate required for normal growth and development of trees,less or equal to the net photosynthetic rate water potential compensation point and approximating to the initial water potential when the quenching of chlorophyll fluorescence decreased with .the leaf water potential decreased. Compared the critical leaf water potential of trees when the total photosynthetic rate,transpiration rate, the chlorlphyll fluorescence parameters were approximating to 0 and the water absorbing capability was losed initially, the critical water potential at the total photosynthetic approximating to 0(ψrpc) could be the minimal water potential for the survival of the tree. Ψrpc related to πp linearly, was the difference in different growth period of trees,used to evaluate the adaptability of trees to the severe water stress. Growth water potential field and life water potential of trees could obtained by πp and Ψrpc. It was important theory and practical significance for the afforestation of the tree under arid and semiarid regions and the research on relationship between plants and water.