Microcoring Based Monitoring The Intra-annual Growth Of Typical Conifer Species In The Humid Subtropics

The humid subtropical climate is sensitive to global changes.The high-resolution historical climate reconstruction based on tree-rings provides an important background for understanding contemporary climate change.Tree growth observation is the basis of tree-ring climate reconstruction.Monitoring the interannual growth of trees have higher solution(month or weekly scale)than annual rings,which can provide higher solution of trees in response to climate change.The research based on the microcoring method,which is more time-consuming but more accurate,to select the subtropical coniferous species of Cryptomeria fortunei and Cunninghamia lanceolate,and conduct a two-year(2016-2017)monitoring in Gu Mountain Scenic Spot,Fuzhou City,Fujian Province.The main findings are as follows:(1)Cambial activity of Cryptomeria fortunei and Cunninghamia lanceolate during 2016 to2017 was started in the early April to mid-April and ceased in mid-October to early November.The length of the growing season is 180-220 days,which is about 3 months longer than temperate and boreal forest,and the temperature at the beginning and end of the growing season is much higher than that high altitude and cold regions.The number of cells in the formation layer and the number of enlargement cells of Cryptomeria fortunei and Cunninghamia lanceolate showed a change of"down bell"shape,which increased and then decreased.The number of cells in the xylem cell shown"S"shape.However,the number of cells in the lignification stage showed two peaks of growth in April-June and September-November.This“bimodal”type is occurs only in the Mediterranean.This“bimodal”type may be caused by the climatic characteristics of the high temperature but low precipitation in the study area during the summer.(2)Combining the physiological characteristics of the Cryptomeria fortunei and Cunninghamia lanceolate and the daily climate data from 2016 to 2107,we conclude that the spring temperature plays a key role in triggering the cambial activities in the study region.Synergistic effects of climatic factors such as temperature,illumination and precipitation may be the reason for cambial region into dormant stage.In access to investigate the relationship between cell enlargement,lignification and xylem cell increment and climatic factors.The enlargement stage and lignification stage of Cryptomeria fortunei were related to temperature but not precipitation.But the lignification and enlargement stage of Cunninghamia lanceolata was related to temperate and precipitation significantly at the same time.However,there were the no obvious relationship of total xylem cells and climate in two conifer species.The binary logistic regression model was used to fit the threshold temperature of the initiation cambial activities of the Cryptomeria fortunei and Cunninghamia lanceolate.The average threshold temperature of the two species was above 16~oC,indicating that the threshold temperature of the tree formation in the subtropical region is higher than that of the temperature and boreal zone.The higher threshold temperature may be caused by the characteristics of the species.It was found that the response of different tree species to the climate was not consistent.(3)The lartewood of Cryptomeria fortunei and Cunninghamia lanceolate in the study area began to appear from the end of May to the beginning of June,which is 3-4months earlier than the temperate and boreal forest.The relationship between the growth of latewood and the precipitation of Cryptomeria fortunei is significant,but the relationship with temperature is not significant,and the correlation between the growth of late wood and the temperature and precipitation is not significant.The rapid rise in temperature may be the trigger for the emergence of late wood in the study area,but specific triggers require further research.In the 2016-2017 study area,both the Cryptomeria fortunei and Cunninghamia lanceolater have a decline rate of latewood,which may be caused by a decrease in precipitation in the autumn leading to the early termination of tree formation activity.