Research On Leaf Hydraulic Traits In Different Canopy Layers Of Populus Tomentosa Under Different Water Treatments

Leaf is the terminal of plant water transport,and its hydraulic characteristics characterize the water survival strategy plants adapting to different external environments.Leaf water potential and stomatal conductance are often used as an important basis to measure the response of plants to different water conditions.In this paper,the triploid Populus tomentosa under the three different water treatment conditions of drip irrigation fully,drip irrigation control and no irrigation were studied.The leaf water potential of the leaves at different heights of the canopy was measured,including the water potential of in noon leaf,the leaf water potential before the dawn and stem water potential,stomatal conductance,leaf water content and other indicators,the hydraulic characteristics of the leaves at different heights of Populus tomentosa were analyzed combined with soil moisture conditions and meteorological factors,.The main results are as follows:(1)The stomatal conductance of the upper layer at noon is larger than that of the middle and lower layers;the stomatal conductance of the leaves in different parts of the canopy basically shows a bimodal curve in the daily dynamics.In the 24-hour dynamic measurement of stomatal conductance,there is a clear "V" shape change trend.Compared with the middle and lower layers,the stomatal conductance change of the upper layer shows a certain hysteresis;(2)?pd of the upper layer is often higher,while the ?zw is higher in the lower layer,and the ?s of the upper layer tends to be lower than the middle and lower layers.There was always no significant difference in leaf water potential among different heights of the canopy.(3)The Gs of the upper layers is more susceptible to VPD,which is associated with three different correlations:positive correlation,negative correlation and irrelevance,and the correlation between Gs and VPD may appear in one day's measurement.In this regard,there are two regulation mechanisms in Populus tomentosa:isohydric and anisohydric mechanism.(4)There was no significant difference in leaf water content and specific leaf weight among different heights of the canopy.(5)Under DIFI and DICI treatments,the leaf water content of the upper canopy is the largest among the different heights of canopy,while the water content in the lower layer is higher than that of the upper and middle layer under the CK treatment(except July 20th).The results above can provide a basis for studying the water conduction and coordination relationship in the root-stem-leaf water transport system of Populus tomentosa.