The Growth Response Of Picea Wilsonii Mast. To Climate Change And Intraspecific Competition In Semi-arid Area

The impact of climate change on tree growth has always been the focus of attention around the world.However,there is currently a lack of studies on the response of tree growth to increased drought and increased atmospheric carbon dioxide concentration on a long-term scale,and the role of competition in regulating tree growth in response to climate variability is also ignored.In this study,in Xinglong Mountain,a semi-arid region of northwestern China,9 Picea wilsonii Mast.standard plots were investigated,and 274 tree cores were collected.Based on the dendroecology method,the above problems were discussed by using the mixed-effect models,regression analysis,correlation analysis and variance analysis.Results found the basal area increment of trees decreased by 28%(from 7.59 to 5.43 cm² year^-1)as the intrinsic water use efficiency increased 32%(from 98.61 to 130.28?mol mol^-1).Despite both C_a and drought positively affected intrinsic water use efficiency,they did not promote tree growth.Meanwhile,values of intercellular[CO₂]increased 14%?from 158.83 to180.89 ppm?while the ratio of intercellular[CO₂]to C_a decreased 7%?from 0.50 to0.46?.In relatively wet years?precipitation>average?,there was no significant difference in climate sensitivity between different competition classes.However,trees suffering from highly competitive stress were more sensitive to climate variability in all years,and particularly in the subset of years that was relatively drought?precipitation<average?.These results suggest that competition enhances its ability to regulate tree growth response to climate variability in adverse weather conditions.Competition for resources between trees was asymmetrical,and an increase in height could give trees a disproportionate benefit.Thus,at trunk-level,both basal area incremental growth and intrinsic water-use efficiency of trees subjected to low competitive stress were significantly higher than trees that are subjected to highly competitive stress.Although the intrinsic water-use efficiency of trees under highly competitive stress increased more rapidly as the drought level increases,this did not change the fact that the radial growth of them declined more.Our research contributes to the understanding of the global carbon cycle and has implications for forest management under climate change.