Study On Stem Radial Variation And Sap Flow Of Qinghai Spruce In The Upper Reach Of The Heihe River

Qinghai spruce（Picea crassifolia Kom.）is the dominate tree species in the Qilian Mountains,and play important roles in ecological service functions in this region,such as water conservation,climate regulation,carbon sequestration and oxygen release etc.It is the main carrier of ecological function in Qilian Mountains.It makes the Qilian Mountains become an important ecological security barrier in Northwest China.Moreover,it is reported that,Qinghai spruce is one of the natural species that whose tree rings can and suitable be used to construct long time series of past climate changes.At present,the research of Qinghai spruce is mostly focused on dendrochronological and hydrology,little research has been done into the high resolution of stem radial variation and sap flow of Qinghai spruce.However,study on the stem radial variation and sap flow under the global climate change,can provide theoretical support for the research of dendroclimatological,can provide theoretical guiding for Qinghai spruce play an effective role in the ecological function of water conservation,and also can provide scientific basis for the sustainable development of Qinghai spruce forest in Qilian Mountains.In this thesis,our study area is the Tianlaochi catchment,which is located in the middle part of the Qilian Mountains,and the upper reaches of the Heihe River.We used measurements of dendrometer,micro-coring and SF-L sap flow sensor,to study the stem radial variation and stem sap flow rate of Qinghai spruce.We found that:（1）The stem radial variation of Qinghai spruce has obvious diurnal cycle pattern,contains shrinkage phase,expansion phase and radial increment phase.It can be divided into the opposite two patterns:growing season and non-growing season.April-September showed growing season pattern,January,February,November and December showed non growing season pattern,March and October are the transition stages of the two patterns.The seasonal dynamics of stem radial variation in a year can be divided into three stages:strong variation,weak variation and moderate variation.（2）The growing season of Qinghai spruce in 2014 is 30^th May to 31^st August,based on the measurement of micro-coring method.This period is corresponding to the moderate variation stage（day of year 148-259）in the seasonal dynamics of stem radial variation.So,the days that the daily average temperature is sustained higher than 5℃,can be regarded as the main growth stages of Qinghai spruce.（3）The stem radial increment sequence extracted by the daily maximum method and daily average method are basically consistent.The radial increment of Qinghai spruce is positively related to precipitation and relative humidity,and is negatively related to daily maximum temperature,photosynthetically active radiation,solar radiation,vapor pressure deficit,daily average temperature,and soil water content.（4）There are significant differences of maximum daily stem shrinkage（MDS）between south side and north side of stem.MDS in south side is greater than that in north side.Temperature is the most important environmental factors affecting MDS of Qinghai spruce.MDS is significantly positively correlated with temperature,solar radiation,vapor pressure deficit and soil temperature,and is significantly negatively correlated with soil water potential.MDS in north side is more sensitive to environmental factors than MDS in south side.（5）The diurnal pattern of Qinghai spruce sap flow rate shows no peak curve in continuous rainy weather conditions,multi peaks curve in the high temperature and dry weather conditions,unimodal curve in humid sunny or cloudy weather conditions.Sap flow rate increased with the increase of stem height below the height of the living branch,however,the law of sap flow rate become more complex above the height of the living branch.（6）Solar radiation,vapor pressure deficit,temperature,relative humidity and wind speed is the main environmental factors that influencing the sap flow rate of Qinghai spruce.The relationship between hourly average sap flow rate and environmental factors is slightly different from the relationship between daily average sap flow rate and environmental factors.（7）The diurnal variation curve of stem sap flow rate shows opposite trend to that of stem radial variation.The relationship between sap flow rate and stem radial variation is different on different time scales,and the best correlation between the two variables was found at the daily time scales.