Radial Growth Of Fraxinus Mandshurica And Pinus Koraiensis On Different Slopes Of Maoershan And Their Response To Climate Change

With the current global warming,along with the increase in temperature,the global precipitation pattern has also undergone significant changes,which has led to a marked increase in the frequency and extent of droughts.To study the effect of drought on the anatomical characteristics and radial growth of the xylem of Pinus koraiensis and Fraxinus mandshurica under different slopes in the Maoershan area of Xiaoxing’an mountain.Long-term fixed-point continuous monitoring methods and wood anatomy methods were used to analyze the radial growth dynamics of trees during the year,and the response of P.koraiensis and F.mandshurica growth to different slopes were analyzed from the anatomical characteristics of the xylem.Subsequently,the response of P.koraiensis and F.mandshurica growth to different slopes climatic conditions were analyzed on the two scales of xylem anatomical characteristics and daily radial growth.The results showed that:The overall change trend of cell parameters in different slopes were basically the same,the vessel number was linear distribution,the maximum vessel area and the total vessel area were generally logarithmic distribution,and the mean vessel area was generally skew-normal distribution.Whereas,there were significant differences in a variety of cell parameters in different slopes,and the vessel number and the vessel area in lower slope were generally larger than that in upper slope.Most anatomical parameters were significantly positively correlated with daily accumulated temperature,but there were also certain differences between the two habitats.The total vessel area of F.mandshurica in upper slope was positively correlated with the daily average temperature,and the vessel number,total vessel area were positive correlation with the relative humidity,and the correlation was greater than that in lower slope;and the minimum vessel area was negatively correlated with the daily accumulated temperature and the relative humidity.While in the lower slope,the total vessel area was significantly positively correlated with the relative humidity.The anatomical parameters of P.koraiensis in the two habitats were more consistent with the response of climatic conditions.Most of the anatomical parameters showed a significant correlation with climate,indicating that the regional warming and drying trend had affected the growth of the main coniferous and broad-leaved trees in the area.The maximum radial growth rate of F.mandshurica was mainly concentrated in mid-July,and the maximum radial growth rate of P.koraiensis was concentrated in the early part of the growing season from March to June.In the early stage of the growing season,the daily radial growth of trees showed a good consistency with temperature.At the end of the growing season,the radial growth gradually decreases with temperature,and there was a certain correlation with precipitation.The temperature during the growing season had a certain inhibitory effect on the radial growth of F.mandshurica,and the gradual increase in daily accumulated temperature had a certain promotion effect on the radial growth of F.mandshurica,and the correlation between lower slope position and climate factors was greater than that of upper slope,indicating that the early temperature of the growing season played a key role.Early in the growing season,the correlation between the daily radial growth of Pinus koraiensis in lower slope and the temperature was greater than that between the upper slope and the temperature,indicating that the temperature promoted the P.koraiensis in lower slope more than the upper slope.Comprehensive studies had found that on an interannual scale,P.koraiensis under relatively dry conditions in the upper slope was more sensitive to hydrothermal conditions,and appropriate temperature and moisture conditions could better promote the radial growth of P.koraiensis upper slope.It followed that the current warm-drying trend had not reached the limit,on the contrary,it had a certain promotion effect on the radial growth of coniferous and broad-leaved trees in the study area.