青檀韧皮纤维生长过程中细胞壁化学组分与力学性能变化OA

In this study,Pteroceltis tatarinowii,an endemic tree species in China,was used to investigate the changes of cell wall physicochemical properties of phloem fibers taken from bark following the tree's growth process.The anatomical structures of the bark and the periodicity of cambial activity in P.tatarinowii were examined using optical microscopy.Safranin and Astra Blue double staining was employed to observe bark anatomy,while Toluidine Blue staining was used to assess cambial activity.Changes in the chemical composition and mechanical properties of phloem fiber cell walls during growth and development were analyzed using micro-Raman spectroscopy and nano-indentation test.The results showed that the bark of P.tatarinowii was composed of mainly three parts,which are periderm,cortex,and phloem.The tangential bands of thick-walled phloem fibers could be observed appearing in the phloem part.After the tree's dormant stage,the cambium cell division activity resumed in early March,and phloem mother cells in the cambium began division earlier than the xylem mother cells.From April to July,the cambium was in the active stage,with the number of cambium cell layers reaching 8-9 layers from 2-3 cell layers during the dormant stage.The cambium entered the transition stage in August with less activity on cell division but changed into the cell wall thickening.The secondary cell walls of phloem fibers commonly contain a gelatinous layer in the bark of P.tatarinowii.Tracing growth and development of phloem fibers,the micro-Raman imaging results showed that carbohydrates accumulated but almost no Raman signal of lignin in gelatinous layer.The signal of the lignin could be firstly detected in the cell corner of phloem fiber,indicating that lignin was firstly deposited at the cell corner.The signal peak of syringyl lignin was detected in the late stage of lignification of cell walls,which may have negative impacts on the delignification treatment in the paper making process.The nano-indentation micromechanics results showed that the modulus of elastic of phloem fiber's cell walls increased during cell wall deposition and then tended to be stable.The modulus of elastic and hardness of cell walls were approximately(15.36±3.05)and(0.56±0.08)GPa,respectively.This research enhances the understanding of the property evolution of the phloem fibers during the bark development in P.tatarinowii,and provides a theoretical basis for the collection,property modification,and high-value utilization of phloem fibers.