Characteristics Of H₂O Vapor Concentration And Hydrogen-oxygen Isotope Dynamics At Different Heights Of Larix Gmelinii Overstory Forests And Their Responses To Environmental Factors

To interpret the dynamic characteristics of H₂O vapor concentration and hydrogen-oxygen isotope changes in the vertical gradient of Larix gmelinii overharvested forest and its response to environmental factors,and to provide a basic theoretical basis for an in-depth discussion of the water exchange process and its mechanism in Larix gmelinii overharvested forest.High-frequency in situ observations of H₂O vapor concentration and its hydrogen-oxygen isotopes(δ¹⁸O,δD)were conducted at four vertical heights of 0.5 m（near surface layer）,2 m（shrub layer）,8 m（tree canopy layer）,and 12 m（background atmosphere）in a Larix gmelinii overstory forest using a hydrogen-oxygen stable isotope technology profile system,and simultaneous observations of air temperature（Ta）,relative humidity（RH）,wind speed（WS）,The environmental factors of air temperature（Ta）,relative humidity（RH）,wind speed（WS）,precipitation（P）,solar radiation（SR）,soil temperature（Ts）and soil water content（SWC）were observed simultaneously to analyze the dynamic changes of H₂O vapor concentration,its hydrogen-oxygen isotopes and environmental factors,and the effects of environmental factors on H₂O vapor concentration and its hydrogen-oxygen isotopes were analyzed by the method of path analysis.The results showed that:（1）The analysis of the daily variation of environmental factors showed that Ta and Ts showed a single-peak variation trend,SR,VPD and WS showed an irregular single-peak variation trend,RH showed a single-valley variation trend,and SWC showed a decreasing trend because the observed weather was continuous sunny days without precipitation supplement;the analysis of their monthly variation showed that Ta,Ts,P,SR and VPD showed an irregular single-peak variation trend,WS showed a decreasing variation trend,and SWC showed a“W”-shaped trend.（2）The daily analysis of H₂O vapor concentration and its hydrogen and oxygen isotopes at different altitudes showed that the H₂O vapor concentration showed an irregular single-peak trend and the hydrogen and oxygen isotopes showed similar trends.There was no intra-day variation（P<0.05）,and inter-day variation was found.The monthly variation of H₂O vapor concentration and hydrogen-oxygen isotopes were found to be unimodal,with the maximum value occurring at the leaf development stage and the minimum value at the leaf drop stage.Both the H₂O vapor concentration and its hydrogen-oxygen isotope composition in the background atmosphere decreased with the increase of vertical height.（3）There was a highly significant positive correlation between H₂O vapor concentration,δ¹⁸O,andδD at different heights（P<0.001）.（4）The response of H₂O vapor concentration and its hydrogen and oxygen isotopes to environmental factors at different heights was found to be different for different heights.The factor with the strongest contribution to H₂O vapor concentration is Ts5（0.910<PC<0.917）,which decreases with increasing altitude.The factor with the strongest promotion effect onδ¹⁸O was Ta（0.781<PC<0.782）,which was strongest at the tree canopy.The strongest promoting factor forδD was also Ta（0.854<PC<0.861）,which weakened with increasing height.The factor with the strongest inhibitory effect on all three was WS,and it increased with height.