| Under the background of global climate change,the southern part of Daxing'anling is on the edge of climate belt,which is greatly affected by climate change,making the death of birch,the representative tree species in this area,increasingly serious,and the recovery ability is poor.The transpiration characteristics of birch species in this area were selected to study,and the utilization strategy of birch stem sap flow to soil water was revealed,which provides a reference for the study of tree drought resistance and water use in the process of ecological restoration in this area.The main results are as follows:(1)Variation characteristics of trunk sap flow density.The diurnal variation of sap flow density shows an obvious diurnal variation law,that is,the variation amplitude of sap flow density in the day is larger than that in the morning and night,while the variation amplitude in the morning and night is relatively smaller,and the sap flow density is slow,but sometimes it is not zero,and the overall variation presents a single peak curve.On the seasonal variation,the sap density first increased and then decreased.(2)Variation characteristics of sap flow density in different diameter classes.Indicating that the tree diameter class has a certain impact on the sap density.In general,the peak value of the average sap density in the small-diameter class is 6.23 cm3·cm-2·h-1,while the peak value in the large-diameter class is 15.67 cm3·cm-2·h-1.During the observation period in 2017,the maximum value oftrunk sap flow density of diameter class A and B appeared in September and August respectively;the minimum value appeared in May and September respectively.During the observation period in 2018,the maximum value of trunk sap flow density of diameter class A and B appeared in May;the minimum value appeared in September.During the observation period in 2019,the maximum and minimum values of trunk sap flow density of diameter class a appeared in May;the maximumand minimum values of diameter class B appeared in June.The seasonal variation isthe lowest in May or September and the highest from June to August.(3)Response of trunk sap density to meteorological factors.Through the analysis of sap density and meteorological factors,it is found that there is a certain time lag between them.The correlation analysis showed that the sap density was positively correlated with RS,VPD and Ta,and negatively correlated with RH.In different years,the correlation coefficients between sap density and meteorological factors were Rs>Ta>VPD>RH.The single factor fitting analysis shows that the sap flow density of trunk conforms to the saturated exponential equation with RS and VPD,the quadratic polynomial equation with TA,and the exponential equation with RH.The regression equations of dry sap density and meteorological factors of Betula platyphylla were established by multiple linear regression analysis.The determination coefficients R2 of the equations were 0.865,0.854 and 0.764.The significance test level P<0.001.(4)Response of trunk sap density to soil moisture.The diurnal variation of trunk sap flow density was higher in the day and lower in the night when the soil water content was relatively sufficient and deficient,which was consistent with the variation of solar radiation and water vapor pressure deficit.Under the same soil water content condition,the sap density of large diameter class is higher than that of small diameter class;under the same diameter class,it shows that the soil water content is relatively sufficient than the relative deficit.In different soil water content periods,the saturation index curve was used to fit the sap density with solar radiation and air water vapor pressure deficit,and the fitting effect can reflect the response law of sap density to meteorological factors. |
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