Responses Of Photosynthetic Physiological Characteristics Of Three Greening Tree Species To Seasons In Northern Mountain Of Lanzhou

In order to explore the response of photosynthetic physiological characteristics of green vegetation in the northern mountain of Lanzhou to seasonal changes,the light response curves of three typical green trees Prunus sibirica,Robinia pseudoacacias and Populus alba were measured in different seasons by Li-6400XT portable photosynthetic apparatus.At the same time,the diurnal changes of net photosynthetic rate?Pn?,transpiration rate?Tr?,stomatal conductance?Gs?,intercellular CO₂concentration?Ci?,photosynthetic active radiation?PAR?,atmospheric temperature?Ta?,air humidity?RH?and other physiological ecological factors were measured,and the seasonal diurnal changes of photosynthetic physiological characteristics and shade tolerance of the three plants were analyzed.Through correlation analysis,the seasonal changes of water use efficiency WUE and light use efficiency LUE of three plants were studied.Through stepwise regression equation and path analysis,the main physiological and ecological factors affecting the net photosynthetic rate of plants were explored.The analysis results show that:?1?The diurnal variation of net photosynthetic rate of P.sibirica and R.pseudoacacias showed a single peak curve,while P.alba showed an asymmetric double peak curve.The diurnal variation of Pn of P.sibirica and P.alba was the highest in summer and R.pseudoacacia was the highest in autumn.On the whole,the seasonal daily average of Pn was the highest for P.sibirica and the lowest for R.pseudoacacia.?2?Among the three tree species,the maximum net photosynthetic rate?Pnmax?of P.alba is higher,and its photosynthetic potential is higher than that of P.sibirica and R.pseudoacacia.The light saturation point?LSP?of R.pseudoacacia is higher than that of Prunus sibirica and P.alba,and that has stronger adaptability to strong light.The light compensation point?LCP?shows that P.sibirica is smaller than R.pseudoacacia and P.alba,and its shade tolerance is higher than that of them,which has certain adaptability and utilization ability to weak light environment.?3?The water use efficiency of P.sibirica in spring,summer and autumn is1.71?mol·mmol^-1,1.73?mol·mmol^-1,1.96?mol·mmol^-11 respectively,and that of R.pseudoacacia in spring,summer and autumn is 4.58?mol·mmol^-1,3.03?mol·mmol^-1?4.66?mol·mmol^-11 respectively.Water use efficiency of P.alba in spring,summer and autumn is 3.05?mol·mmol^-1,7.29?mol·mmol^-1,3.99?mol·mmol^-11 respectively.On the whole,P.sibirica is the highest in autumn,followed by summer and the lowest in spring.R.pseudoacacia is the highest in autumn,followed by spring and the lowest in summer.P.alba var.pyramidalis is the highest in summer,followed by autumn and the lowest in spring.The seasonal daily average of WUE is highest for P.alba and lowest for P.sibirica.?4?The light energy utilization rate LUE of P.sibirica in spring,summer and autumn is 1.01%,1.12%and 1.09%,that of R.pseudoacacia in spring,summer and autumn is 0.43%,0.51%and 0.33%,and P.alba in summer and autumn is 1.26%,1.47%and 1.41%respectively.On the whole,the LUE of P.sibirica and P.alba showed the highest in summer,followed by autumn and the lowest in spring.The LUE of R.pseudoacacia is the highest in summer,followed by spring and the lowest in autumn.On the whole,the seasonal daily average of LUE was the highest for P.alba and the lowest for R.pseudoacacia.?5?Path analysis showed that The main determinant of P.sibirica Pn is PAR in spring and summer,and leaf vapor pressure difference?Vpdl?was in autumn,the main limiting factors in spring and summer are soil temperature?Ts?and Ta respectively;The main determinant of R.pseudoacacia Pn is Tr in spring and autumn,and Vpdl was in summer,the main limiting factors in sumer and autumn are Tr and Ts respectively;The main determinant of Pn in P.alba is Tr in spring and summer,and Gs in autumn,the main limiting factors in spring and autumn are Ts and RH respectively.Comprehensive analysis showed that the three greening tree species showed positive growth patterns with seasonal changes,among which the growth patterns of P.armeniaca and P.alba in summer were better than those in spring and autumn,and the growth patterns of R.pseudoacacia in autumn were better than those in spring and autumn.Among the three tree species,P.alba has stronger adaptability than R.pseudoacacia and P.sibirica,while P.sibirica has the strongest shade tolerance.The results of this study can adopt corresponding cultivation measures for different vegetation types in the northern and southern mountains of Lanzhou to improve their photosynthetic performance and achieve rational utilization of resources and optimal greening effect.At the same time,the adaptability of the three plants was evaluated to provide a theoretical basis for the introduction,cultivation and application of P.sibirica,R.pseudoacacias and P.alba.