慈竹微观构造及细胞壁化学组成径向变化规律OA

Neosinocalamus affinis,an important bamboo species predominantly used for papermaking in regions such as Sichuan and Guizhou Provinces in China,was systematically analyzed to explore its fiber potential for high-valued applications.In the present work,the gradient variations in microstructure and cell wall chemical composition of N.affinis were investigated using advanced microscopic imaging techniques.These findings offer deeper insights into the bamboo biomass characteristics,supporting its broader utilization in value-added products.Light microscopic images revealed that the fundamental structural unit of the bamboo stem was vascular bundle,which was embedded within porous parenchyma tissue.Each vascular bundle comprises a fiber sheath,vessel,sieve tube,and companion cell.The average fiber diameters in bamboo green,bamboo timber,and bamboo yellow regions were 1 903.72,1 658.47 and 1 689.94 μm,respectively.In contrast,the morphology of the parenchyma exhibited significant variation across these regions.It was revealed that the vascular bundle density in N.affinis gradually decreased from the bamboo green toward the bamboo yellow,but the proportion of non-fiber cells increased from 35.2%to 71.3%.The bamboo fiber aspect ratio reached 123 at the bamboo green,which was higher than that of softwood and hardwood.It was also found that the wall cavity ratio declined from 4.26 at the bamboo green to 2.68 at the bamboo yellow.Moreover,considering its higher spatial resolution and spectral resolution of confocal Raman microscopy,the distribution pattern of carbohydrates,cellulose,lignin and hydroxycinnamic acid esters(HCA)was visualized in situ.Raman images by integrating over the C-H stretching band at 2 942 cm-1 clearly distinguished fibers from parenchyma and identified the distinct structural sublayers within the fiber walls,including the cell corner middle lamella,compound middle lamella,secondary wall,and alternating broad-narrow layers of the secondary wall in fibers.Raman imaging further demonstrated that lignin(1 605 cm-1)and HCA(1 172 cm-1)were primarily distributed in the middle lamella and the narrow layers of fiber secondary walls,while carbohydrates(2 897 cm-1)and cellulose(380 cm-1)were concentrated in the fiber and parenchyma secondary walls.Semi-quantitative analysis of Raman spectra indicated that fibers contained higher concentrations of carbohydrates and cellulose,whereas parenchyma were richer in lignin and HCA.At sub-cellular level,there was a decreasing trend in lignin and HCA concentrations within the successive broad layer of fiber secondary walls from the bamboo green to bamboo yellow,while carbohydrates and cellulose concentrations displayed an opposite tendency.These results offer valuable insights into the microstructural and compositional characteristics of N.affinis,providing a robust data foundation for comprehensive utilization of bamboo resources in various applications.