| The sap flow is an important indicator for studying the water use status of trees and calculating the water consumption of trees by transpiration.In this study,the thermal diffusion probe method was adopted,the site conditions were set in the sandy land in eastern Hebei,and 107 fast-growing poplars were used as test trees,monitor the trunk sap flow rate during the main growing season(May-October),and monitor environmental factors and tree growth factors at the same time,analyze the main change characteristics of trunk sap flow and the response relationship to each factor,and clarify the water use characteristics of fast-growing poplar on the sandy land in eastern Hebei.It is of great significance to discover the water consumption law of artificial fast-growing and high-yielding forests on sandy land and to formulate reasonable irrigation strategies.Below are key research findings:(1)On the hour scale,the trunk sap flow of Populus×euramericana cv.’74/76’mainly showed a "ji"-shaped curve,the overall performance of each month is August>July>June>May>September>October,the trunk sap flow in the middle of the growing season in July and August has the characteristics of early start time,high peak value,long duration,and large accumulation of sap flow,which is the main growth stage;On the daily scale,the tru nk sap flow rate of Populus×euramericana cv.’74/76’ showed an irregular curve,according to the fluctuation degree of the growth period from large to small,it appears as the middle of the growing season(July-August)>the early period of the growing season(May-June)>the latter part of the growing season(September-October),the accumulation of the trunk sap flow reaches its maximum in July,The smallest month in October;On a monthly scale,both the monthly scale change and monthly accumulation of trunk sap flow showed a trend of first increasing and then decreasing,reaching a maximum in August and then decreasing.(2)The change of trunk sap flow in typical weather is sunny>cloudy>rainy;The change of trunk sap flow under different soil moisture is in the order of sufficient soil moisture(15%～20%soil volume water content)>moderate moisture(10%-15%soil volume water content)>water deficit(5%～10%soil volume water content);There is a time lag effect between the trunk sap flow on various meteorological factors.The trunk sap flow lags behind the solar radiation by 40 minutes and advances the temperature,relative humidity,and VPD(water vapor pressure deficit)by 60 minutes.The trunk sap flow and VPD show a "hysteresis loop" relationship,after the time lag dislocation,the meteorological factors have a significant driving effect on the trunk sap flow,the trunk sap flow has the greatest correlation with air temperature during the day,and has a strong driving force,while at night,it has the greatest correlation with VPD and has a strong driving force;The fitting effect of trunk sap flow and meteorological factors after time lag dislocation is better than that before time lag dislocation.(3)The response of the trunk sap flow to the crown width is mainly manifested as the larger the crown width,the earlier the sap flow starts,the higher the peak value,and the longer the duration;The response of the trunk sap flow to breast diameter is mainly manifested as the larger the breast diameter,the earlier the stem trunk sap flow starts and the greater the fluid flow,but there is no linear relationship between breast diameter and the trunk sap flow rate;The response of sap flow to the root system is that whether it is root length density,root surface area,or specific root length,it shows that the root growth and development on the west side of the wide row has advantages,at the same time,the trunk sap flow rate on the west side is significantly different from other directions,indicating that the trunk sap flow has a stronger response to the root system;The response of sap flow to the radial growth of trees is that the trunk sap flow is negatively correlated with the radial growth of the trunk and roots as a whole,there is a significant correlation between the contraction phase and the growth phase.The growth phase has a greater correlation,and the correlation between the trunk is greater than that of the root,and the response degree is stronger.In the recovery phase,the correlation is not significant and the response degree is not strong.(4)Irrigation strategy based on trunk sap flow:The drip irrigation method is used for irrigation,and the flow rate of the dripper is set to 1.6L·h-1.Irrigation should be carried out mainly for the 0-40cm of the soil surface.The dripper is concentrated at the base of the trunk to ensure that it is supplied to the 1m area around the trunk,and a small amount of irrigation should be carried out several times.Irrigation should be concentrated in the tree growing season(May-October),and the middle of the growing season(July and August)is the key irrigation period.Set the irrigation interval to 5d under no rainfall conditions,in case of sufficient rainfall,the interval should be calculated again from 0,if the rainfall is low;the interval can be appropriately extended by 1～2d;Make sure that the duration of each irrigation is about 6h;For trees with large breast diameter and crown width,the irrigation time can be extended to 6.5h-7h;With the growth of the forest age,the deep-seated irrigator can be used to replenish the deep soil moisture;When the irrigation interval is 4 days,a small amount of water can be supplemented at night for about 1 hour to meet the needs of plants to supplement water to the stems at night. |
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