Study On The Characteristics Of Transpiration And Water Consumption Inspruce Forest Of Qilian Mountains

Tree transpiration and water consumption in arid and semi-arid regions have an important impact on the ecological and hydrological processes of the river basin.In recent years,the global climate has increased and the precipitation pattern has changed,which is bound to have an impact on the growth of trees.A deep understanding of the law of transpiration and water consumption can provide technical support for the healthy growth of vegetation and forest management in Qilian mountains.This paper first explored the method of measuring the sap flow,and compared with the multifunctional digital penta needle heat pulse probes and the thermal diffusion probe to determine the sap flow,so as to provide technical support for the determination of the sap flow of tree.Then,the relationship between physiological growth and soil moisture in Picea crassifolia was investigated on a small watershed scale,while the characteristics of sap flow and its influencing factors of Picea crassifolia were analyzed on a single plant scale by thermal diffusion method.The characteristics of soil water storage and forest water circulation were analyzed by simulating the change of precipitation.The specific research results are as follows:A new multifunctional digital penta needle heat pulse probes(PHPP)was selected to measure the sap flow of the Lobular poplar by using the theory of thermal pulse.The results showed that both PHPP and TDP could accurately reflect the law of diurnal variation of sap flow,and the measurement results showed a significant linear correlation,with R~2 reached0.90,root mean square error was 2.75 and mean relative error was11%.PHPP probe can accurately identify low and reverse sap flow,can quickly and accurately fit the thermal parameters,and directly measure the sap flow rate,while TDP method has the advantage of simple probe.Forest degradation was found in the Qinghai spruce forest in this basin.The soil water storage in the root region of the degraded forest region was high and showed no water shortage.However,the photosynthetic rate and transpiration rate of Qinghai spruce were significantly lower than those in healthy forests.The water potential of spruce branches in the degraded area was-4 MPa,exceed the threshold value,result in hydraulic conduction loss.The density of Qinghai spruce is too high,so the comprehensive effects of aging,diseases and insect pests and wind damage led to the decrease of physiological regulation ability of Qinghai spruce in forest area,which affected the healthy growth of Qinghai spruce.The starting and ending time of Qinghai spruce sap flow is consistent with the change trend of solar radiation,but there is a certain time lag with the change of solar radiation and temperature.The daily change curve of sap flow rate presents a peakless curve in rainy days,with a small change range and a large change range in sunny days,and presents a multi-peak or single-peak curve due to the difference of solar radiation.The Qinghai spruce flow in sunny days starts earlier,ends later and has a larger peak.The average sap flow density of Qinghai spruce first increased and then decreased in growing season.In addition to the influence of solar radiation,VPD,air temperature,wind speed and other meteorological factors,the average sap flow density of Qinghai spruce is also closely related to soil temperature and soil moisture content.The simulated precipitation treatment significantly increased the water storage in the forest from 0 to 100 cm by 20%,and the transpiration water consumption of spruce increased by 22.2%.Compared with the control,there was no significant difference between the water storage in the soil from 0 to 100 cm and the transpiration of spruce.Qinghai spruce has strong adaptability and the short-term drought has no effect on the vegetation growth and transpiration water consumption of Qinghai spruce.