Study On The Tree Ring Growth Of Japanese Cryptomeria And Its Response To Environmental Changes In Lushan Mountain Based On Stable Isotopes

In this study,the tree cores of Japanese cryptomeria at three different elevations(850m,1050m and 1250m)in Lushan mountain nature reserve of jiangxi province were selected as research materials by dendrography.By measuring the tree ring width,stable carbon isotopes(δ13C),stable nitrogen isotope(δ15N)and establish the standard chronology(STD),calculate water use efficiency(WUE),to explore the growth rule of Japanese cryptomeria and its influenced factors under the background of global climate change,atmospheric CO2 concentration doubling and increasing nitrogen deposition,for the study of subtropical moist climate change under the condition of Japanese cryptomeria provide theoretical basis for the impact of growth and distribution.Furthermore,it provides technical support for the forest sustainable management in response to climate change in Lushan nature reserve and the whole subtropical region.The main research conclusions are as follows:(1)The response of tree ring width to climatic factors of Cryptomeria japonica at low elevation(850m)was more sensitive than that at middle(1050m)and high elevation(1250m).There was a significant positive correlation with spring relative humidity(P<0.05)at low elevation and middle elevation,a very significant negative correlation with sunshine hours in spring and autumn mean temperature(P<0.05)at low elevation,a significant negative correlation with summer mean temperature and autumn mean temperature at middle elevation(P<0.05).There was a certain correlation with climate factors in each season at high elevation,but the correlation was not significant.There was a significant positive correlation with mean temperature of three different elevations in January(P<0.05),a significant negative correlation between the mean temperature in July of previous year and July of that year at low elevation and middle elevation(P<0.05).High temperature would inhibit the growth of trees.Besides,a very significant negative correlation with the relative humidity,precipitation(P<0.05)and a significant positive correlation with sunshine hours(P<0.05)in April at low elevation,but decreased with the increase of elevation.The correlation between the radial growth of Cryptomeria japonica and the main climatic factors in Lushan Mountain was obvious seasonal,the radial growth of Cryptomeria japonica was mainly influenced by the temperature in July and July of the previous year and the relative humidity in April.(2)There was a significant negative correlation between the tree ring stable carbon isotope sequence(Δ13C)of Cryptomeria japonica and the temperature in August,sunshine time in July,August of the previous year at low elevation(850m)(P<0.05),but there was significantly positive correlation in the January precipitation(P<0.05).There was a significantly negative correlation betwwen the tree ring Δ13C of Cryptomeria japonica and the sunshine time in August and in July and August of the previous year at middle elevation(1050m)(P<0.05),there was no significant correlation in the monthly mean temperature,the monthly precipitation,relative humidity.There was a significantly negative correlation between the tree ring Δ13C of Cryptomeria japonica and the mean temperature in March and in September of the previous year at high elevation(1250m)(P<0.05),a significantly positive with the relative humidity in March and April(P<0.05),no significant correlation with precipitation and sunshine time.The tree ring Δ13C sequence of Japanese cryptomeria showed a strong "hysteresis" effect,which was consistent with the research on the response of the tree ring width to climate factors.The water use efficiency(WUE)of Japanese cryptomeria at different elevations increased with the growth of the trees.But During the initial growth period(1969-1985),the water use efficiency of Japanese cryptomeria decreased,in the subsequent growth stage(1985-2013),the water use efficiency of Japanese cryptomeria increased significantly(P<0.05).The water use efficiency of Japanese cryptomeria began to decrease to a certain extent from 2013 to 2018,The change trend of the water use efficiency of Japanese cryptomeria at different elevations was consistent.There was a significant correlation between WUE and monthly mean temperature,monthly precipitation,relative humidity,monthly sunshine hours and atmospheric CO2 concentration at three different elevations(P<0.05).(3)Changes in the ring tree δ15N of Japanese cryptomeria at different elevations over the years are shown as follows:The ring tree δ15N of Japanese cryptomeria tends to increase first and then decrease with the elevation increasing.The ring tree δ15N of Japanese cryptomeria in low and high elevation areas is the most sensitive to the change of climate factors,mainly manifested in the change of sunshine hours and monthly mean temperature.Changes in the ring tree δ15N of Japanese cryptomeria at middle elevation can better indicate the impact of traffic emissions on tree ring growth.(4)The elavation,CO2 concentration,nitrogen deposition and climate factors are important factors affecting the tree ring growth of Japanese cryptomeria.