Research On Tree-ring During Tree Growth

Over the past three decades,the upward trend of global warming has caused a plethora of extreme weather events,leading to severe disasters in social and economic development and endangering human life.Since tree growth is closely linked to the local climate,tree-rings serve as a natural ’weather station’,displaying structural changes in respond to climate change and recording the traces and trends of climate and environmental changes.Thus,this study chose tree disks of Styphnolobium japonicum,Robinia pseudoacacia,Pinus massoniana and Podocarpus macrophyllus as the research objects,and utilized contemporary analysis techniques,such as Linear Tree-ring Measuring Stage(Lin Tab),Computed Tomography(CT),Scanning Electron Microscope(SEM),Energy Dispersive X-Ray Fluorescence Spectrometer(ED-XRF)and Pyrolysis-Gas ChromatographyMass Spectrometry(Py-GC-MS)to systematically examine the characteristics of tree-rings and elucidate their association climate change.The findings are as follows:(1)Dendroclimatology studiesCombined with local meteorological data,the standardized tree-ring width chronology and its combined chronology were established to study the fluctuation cycle of the tree-ring index and the correlation with monthly average temperature and precipitation.The result of combined chronology analysis showed that quasi-periodic fluctuations of 10 years in the annual ring index,closely related to sunspot activity.According to the magnitude of the annual ring index in each cycle,the special rings with normal radial growth and promoted and inhibited radial growth were selected.Correlation analysis between the combined chronology and climatic factors revealed that the radial growth of trees in Zhumadian area was mainly affected by average temperature in July(r=0.283,P<0.05),precipitation in Dec.(r=0.349,P<0.05)and precipitation in Oct.(r=0.259,P<0.05).At the same time,according to the annual precipitation variation rate and historical data of drought and flood disasters in Zhumadian area,the climatic conditions of trees with narrow tree-rings are proved.When tree growth is inhibited and promoted,the value range of parameter |Qi-1+Qi|/2 is greater than 20% and 10%–20%,respectively.Additionally,examining the variation of the annual ring index can help infer local climatic conditions,with significant narrow rings indicating possible serious drought or flood disasters in the current or previous year,and annual precipitation less than 576 mm or higher than 1344 mm.(2)Tree-ring graphics studiesIndustrial CT were used to scan tree disks,reconstructe 3D images and observe the internal structure of tree-rings.The earlywood and latewood of R.pseudoacacia tree-rings was trained using deep learning models,and after many trainings and adjustments,the "Seg Wiz_R-Forest_A-M-2" algorithm was found to have the best recognition effect,with a segmentation accuracy of 0.9824.Then,tree cores after cutting CT images of S.japonicum,R.pseudoacacia,P.massoniana and P.macrophyllus used to obtain their gray values,and the resulting grayscale curves from pith to bark are plotted.The density change of tree ring was analyzed by using gray scale instead of density indirectly.The growth of P.massoniana was promoted in 1991,and the maximum density of latewood(MXD)was relatively low.The growth was inhibited in1993,and the MXD should be the highest.However,due to the serious floods,the latewood of tree-ring may stop growing in advance,prompting the MXD to decrease.In 1996,the ring index was close to 1,the growth was normal,and the MXD was close to the average.At the same time,it was found that the maximum density of latewood of P.massoniana tree-ring was significantly different,which was very suitable as a surrogate index for reconstructing past temperature.There is a great difference in the minimum density of earlywood between S.japonicum and R.pseudoacacia,which can be used as a substitute index for reconstructing past precipitation.(3)Dendrochemistry studiesEDXRF analysis was conducted on tree-ring fragments of S.japonicum,R.pseudoacacia,P.massoniana and P.macrophyllus,revealing the presence of 13 inorganic elements.Among them,S,K,Ca,Cu and Zn were found to have higher contents than the detection limit,and their relative content exhibited a complete time series.The analysis shows that S has the highest coefficient of variation in R.pseudoacacia and played a significant role in absorbing SO2.Although the absorption of K and Ca was not evident,the coefficient of variation of heavy metals Cu(0.134–0.255)and Zn(0.298–0.512)was higher,indicating moderate variability.In addition,the relative contents of S,Cu and Zn elements have a significant increasing trend.Py-GC-MS analysis of special tree-rings of S.japonicum,R.pseudoacacia,P.massoniana and P.macrophyllus identified 114,98,84 and 72 compounds,respectively.The number of pyrolysis components was inhibited tree-rings > promoted tree-rings > normal tree-rings,and the relative content of chemical component categories is alcohol/phenols > aldehydes/ketones > acids > esters.The results of pyrolysis composition Venn diagram revealed that there were 23 kinds of common chemical constituents in the special tree-rings of S.japonicum,while 14 kinds of common chemical constituents in the special tree-rings of R.pseudoacacia,including 11 kinds of common compounds of both such as d-Mannose,Acetic acid,Hydroxyacetone,[1,2-Cyclopentanedicarboxylic acid,4-(1,1-dimethylethyl)-,dimethyl ester,(1α,2β,4β)-] and 3-Hydroxylauric acid.There were 25 kinds of common chemical constituents in special tree-rings of P.massoniana,while 23 kinds of common chemical constituents in special tree-rings of P.macrophyllus,including 16 common compounds of both such as Hydroxyacetone,Acetic acid,[1,2-Cyclopentanedicarboxylic acid,4-(1,1-dimethylethyl)-,dimethyl ester,(1α,2β,4β)-],3-Hydroxylauric acid,2-Methoxy-5-(1-propene-1-yl)phenol.