Intra-annual Stem Radial Growth Dynamics Of Three Coniferous Species In Response To Climate In The Eastern Qilian Mountains

The Picea crassifolia Kom,Juniperus przewalskii,Picea wilsonii and Pinus tabulaeformis distribute widely in the northwest China,and the bad and fragile ecological environment makes the areas become a hotspot of tree-ring ecology and climate research.Dendroclimate researches are based on calculating the correlation coefficient between tree-ring width and meteorological data,getting the main limiting factors affecting the radial growth of trees,and then establish the transformation equation based on the principle of uniformitarianism to reconstruct paleoclimate,troditionally.However,with the discovery of "divergence problem",and the establishment of tree physiological model,the researchers found that the relationship between tree radial growth and climate is nonlinear,this poses a challenge to the traditional tree-ring climate reconstruction.Therefore,it becomes a focus that the researches of the physiological processes of stem radial growth and the mechanism of recording climate information..Next,Picea wilsorii,Pinus tabulaeformis and Juniperus przewalskii trees were continuously monitored with Dendrometer in the Tulugou National Forest Park in the eastern Qilian Mountains from 2013 to 2015 in this study,to provide physiological monitoring support for the research of tree-ring climate response.The following conclusions are mainly drawn:Because of the reversible stem shrinking and swelling,it's hard to distinguish between the true growth signal and hydrological swelling and shrinking,especially the time scale is short(1-day).Therefore,the time scale that extracted stem radial increment was extended to 7 days.It's found that the stem radial increment is positively correlated with precipitation at different time scales,showing that the available water status is a major limiting factor for stem radial growth.However,the correlation coefficient decreased with the extension of time scale,showing that the extension of the time scale can weaken the disturbance of the diurnal variation of the trunk water.To further understand the major climatic factors affecting radial growth,we calculated the moving correlation coefficient between the daily radial growth and the daily meteorological data(temperature,precipitation,VPD)with the window of 31 days.We found that the stem radial increments of tree conifer species are significantly positively correlated with precipitation in May and July during the three years,but the relationship with precipitation in June is different in three years,especially Picea wilsorii and Pinus tabulaeformis.The change of available water is large to radial growth during the three years,so,the relationship between the stem radial growth and precipitation in June is unstable.The correlation coefficient is high when there are abundant precipitation,or it's low.This may be the reason why the relationship between tree-ring and precipitation in June is not significant in some studies on climate response of tree-ring.The current monitoring results are not enough to accurately explain the relationship between the radial growth of the Juniperus przewalskii and the precipitation in June,and we need to monitor continuously.It's found that tree-ring width is significantly correlated with at the end of the previous year.The climatic conditions in the previous August might have an effect on the photosynthesis of trees,thereby influence reserve storage for the second year,but this conclusion lacks a physiological basis.Therefore,we measured the leaf net photosynthetic rate of three conifer species in different time.It's found that radial growth rate is highest at the end of May and early of June,but the net photosynthetic rate is lowest this time,three conifer species have stopped the radial growth in August and September,the net photosynthetic rate is highest instead.It suggested that the photosynthetic products accumulated at the end of previous growing season greatly promoted the radial growth of the early current growing season.The increment of air humidity at the end of the growing season can promote leaf photosynthetic,ensuring the accumulation of photosynthetic product,influencing the radial growth of trees in the coming year indirectly.