Investigation On Tree Growth-lifespan Trade-off Pattern Through Climatic Sensitivity Analysis

Forests are important terrestrial carbon sinks,playing a significant role in global carbon cycling and mitigating climate warming.However,the physiological mechanisms underlying forest carbon sequestration remain unclear,particularly regarding the effects of tree structural growth and population dynamics on carbon sequestration capacity.Recent studies have identified a significant feedback mechanism between tree growth and lifespan at a global scale,where an increase in individual tree growth rates shortens their life cycle,subsequently affecting carbon residence time in forest ecosystems.Analyzing and interpreting this phenomenon from a plant physiological ecology perspective is crucial for accurate assessment and prediction of forest carbon sinks.This study utilizes multi-source tree-ring and climate data from around the world to calculate the sensitivity of individual tree growth to key climate factors and their distribution during the period 1950-2016.The research examines and analyzes the relationship between tree growth and lifespan,as well as the causative factors and influences on this feedback mechanism,across different scales,including the overall scale,climate zones,tree phylum,species,and site levels.The results indicate that:(1)The climate sensitivity of tree growth increases with early growth rate:The median temperature sensitivity ranges from 0.0352 to 0.152 mm/°C and 24.4 to 166 mm~2/°C for the low to high early growth rate groups(G1-G4)in ring-width index(RWI)and basal area increment(BAI)results,respectively;precipitation sensitivity ranges from 0.00345 to 0.00975 mm/mm and 2.28 to10.8 mm~2/mm,respectively;and SPEI sensitivity ranges from 0.0637 to 0.286 mm/SPEI and 42.6to 107 mm~2/SPEI,respectively.The differences between groups are highly significant(P<0.001),with an increasing trend.(2)The climate sensitivity of tree growth decreases with age:In the RWI and BAI results,the median temperature sensitivity ranges from 0.0592 to 0.115 mm/°C and 65.9 to 94.5 mm~2/°C for the low to high age groups(A1-A4),respectively;precipitation sensitivity ranges from 0.00714 to0.0492 mm/mm and 4.82 to 5.74 mm~2/mm,respectively;and SPEI sensitivity ranges from 0.110to 0.207 mm/SPEI and 122 to 159 mm~2/SPEI,respectively.The differences between groups in RWI results are significant(P<0.01),with a decreasing trend.In BAI results,temperature sensitivity and SPEI sensitivity differences are significant(P<0.01)between all groups except for A3(group of tree individuals with ages between the third quartile and median)and A4,with a decreasing trend;precipitation sensitivity differences are significant(P<0.05)but without a clear trend.(3)The climate sensitivity of tree growth increases with size:In the RWI and BAI results,the median temperature sensitivity ranges from 0.0354 to 0.124 mm/°C and 17.2 to 179 mm~2/°C for the small to large size groups(S1-S4),respectively;precipitation sensitivity ranges from 0.00382to 0.00791 mm/mm and 1.78 to 11.7 mm~2/mm,respectively;and SPEI sensitivity ranges from0.0667 to0.235 mm/SPEI and 31.3 to 110 mm~2/SPEI,respectively.The differences between groups are highly significant(P<0.001),with an increasing trend.(4)Further analysis of representative sites reveals that groups with high early growth rates and larger sizes typically exhibit significantly higher interannual growth fluctuations and stronger responses to environmental changes,particularly extreme climates.However,no significant differences are observed in interannual growth fluctuations and environmental responses among groups of different ages.In conclusion,this study finds that trees with higher early growth rates generally exhibit higher climate sensitivity,making them more susceptible to adverse environmental conditions.This phenomenon is likely due to rapid size increase resulting from high growth rates.Furthermore,longer-lived trees typically have lower growth rates and climate sensitivity.The findings will contribute to the explanation of the feedback mechanism between early tree growth and lifespan,which has positive implications for future forest carbon stock assessments and improvements to vegetation dynamic models.Additionally,the results provide a more accurate basis for global carbon cycle research and forest management.