Study On Annual Growth Dynamics Of Xylem Of Pinus Massoniana Of Different Ages In Sanming Area Of Fujian Province

Tree ring is widely used in the reconstruction of climate change in the past millennium.Tree ring reconstruction provides a long-scale climate background for understanding contemporary climate change.The annual growth process monitoring of tree ring is helpful to understand the process of tree ring responding to climate and lay the foundation for the reconstruction of tree ring climate.As a sensitive area in response to global climate change,the subtropical monsoon climate region in China can provide the oretical support for the reconstruction of climate change by monitoring the tree growth dynamics on a weekly scale and studying the tree growth climate response on an interannual scale.In this paper,the more accurate monitoring method in tree growth was used to monitor three different age groups of Pinus massoniana in Geshikao forest park in Sanming city of Fujian province for a period of one year(2019).The cores of Pinus massoniana of corresponding age groups were collected and three tree ring width chronologies were established.The main results are as follows:(1)The beginning time of cambium activity of young and middle-aged tree in the study area is about one month earlier than that of old tree,and the growth season length is about three months longer than that of old tree.The total growth season length of tree in the study area is 3-6 months longer than that in the temperate and cold zone.The dynamic changes of cells in different stages of lignification were similar: enlarged cells showed "inverted U" changes,mature cells showed "S" changes which is consistent with the previous research results.Cell wall thickened cells showed "Bimodal" changes,which may be due to the drought stress of trees in summer,indicating that cambium activity is more sensitive to climate change.The "bimodal" change may come from the drought stress of trees in summer.Gompertz simulation results showed that young and middle-aged tree had higher average growth rate and maximum growth rate,while the cell growth period of old tree was more concentrated.(2)The results of correlation analysis between phenological characteristics of tree at different ages and daily meteorological data in 2019 show that temperature is more closely related to the two stages of xylogenesis,and the minimum temperature has more obvious limiting effect on cell expansion and intra-annual diameter growth.The differentiation and growth of xylem of old tree show higher sensitivity to climate change.(3)The results of correlation analysis between the variation of tree width at different ages and the monthly meteorological data from 1976 to 2018 show that the average temperature in winter-spring,the average temperature in summer,the maximum temperature and precipitation have a strong restriction on the young tree;the average temperature,the maximum temperature and the minimum temperature in winter-spring,the average temperature and the maximum temperature in summer have a greater influence on the middle-aged tree;the average temperature in winter and spring,the maximum temperature and the minimum temperature in summer have a greater influence on the middle-aged tree;the minimum temperature and precipitation in December have certain effects on the old tree.The radial growth of the old tree is more sensitive to climate change on the intra-annual scale,while the young tree is more sensitive to inter-annual climate change.The difference between the intra-annual and inter-annual climate states may lead to the difference in sensitivity.With the increase of tree age,the inter-annual climate sensitivity decreases,which makes climate reconstruction in subtropical areas more challenging.