Climate Response Mechanism Of Radial Growth Of Qilian Juniper

Trees are closely related to human production and life.In recent years,global climate change has a significant impact on tree growth.For example,drought causes tree growth to decline or even die,warming causes the change of phenology of trees,regional warming and humidification promotes radial growth of Picea crassifolia,etc.the change of temperature and humidity has a huge impact on tree growth.Qilian Mountain is a typical cold and arid area in Asia,and also a water conservation area in the Hexi corridor.It has a very important geographical location.Qilian Mountain is located in the junction of the Westerlies,monsoon,and plateau climate zones.The change in the intensity of the monsoon and westerlies will have a great impact on the growth of regional trees.Qilian juniper(Juniperus przewalskii)is a typical coniferous tree species in the arid and semi-arid area,which has the characteristics of drought resistance,cold tolerance,and climate sensitivity.Therefore,this paper mainly discusses the influence of climate change(especially the change of temperature and humidity)on the radial growth of Qilian juniper(Juniperus przewalskii)? What is the physiological mechanism?In this paper,tree-rings of Qilian juniper in six sample sites on the northern slope in Qilian Mountain were collected in the field,and the data of tree-rings of Qilian juniper in six sample sites on the southern slope in Qilian Mountain were downloaded from the International Tree-ring Database.According to the international tree-ring chronology method,we have established 12 standard chronologies by using the ARSTAN program.Based on the tree-ring width data and meteorological data,the response of radial growth of Qilian juniper in different regions to climatic factors was analyzed.The results showed that:firstly,the radial growth of Qilian juniper is positively correlated with the precipitation from May to June and July to September of last year,and also with the drought index.Secondly,in the wetter north slope,the radial growth of Qilian juniper is positively correlated with the temperature in winter and spring;in the drier south slope,the radial growth is negatively correlated with the temperature in growing season.At present,most of the studies on the response of radial growth climate factors of Qilian juniper are based on the linear correlation,lack of explanation of tree physiology.The Vaganov-Shashkin(V-S)model considers the relationship between external environmental factors and the growth process of cambial cells and simulates the effect of external environmental factors on the radial growth of trees.In this study,the V-S model was used to simulate the cambial cell activities of Qilian juniper,and the radial growth of Qilian juniper was studied.The simulation results were rather consistent with the existing monitoring results,which showed that the simulation results of this model are reliable.The specific results were as follows: Soil moisture affects the radial growth rate of Qilian juniper and the length of the growing season,and temperature affects the radial growth rate.With the time going on,the radial growth rate of Qilian juniper increased and the growth season prolonged,which may be caused by regional warming and humidification.The results of this paper will help us to better understand the response mechanism of the radial growth of Qilian juniper to the climate and better understand and predict the changes of the forest ecosystem in the Qilian Mountain Nature Reserve under the climate change scenario.