ObjectiveThe variation of micromorphology, chemical composition and functional groups of marigold straw was studied to provide scientific and reasonable technical basis for the utilization of crop straw at the micro-scale and molecular level.
MethodField emission scanning electron microscopy (FE-SEM) and energy dispersive spectrometer (EDS) were used to characterize the microstructural variation and chemical element composition difference of the cross section of marigold straw. The cell wall percentage of marigold straw was measured by color image computer analysis system. And the functional group distribution rule of marigold straw along the direction of height was characterized by Fourier transform infrared spectrometer (FTIR), second derivative infrared (SDIR) and two-dimensional correlation infrared (2DIR).
ResultThe results showed that: (1) the radial size of marigold straw had a small variation in the upper part (range 7.3), but a large variation in the middle and root (range 10.0 and 10.7, respectively). (2) The upper structure of marigold straw was “sparse”, but the diameter and distribution of tube holes in the middle and lower segments were not significantly different. The type of catheter was mainly single-tube or complex tube. The carbon and oxygen ratio of marigold straw was 0.73, 0.79 and 0.83 from tip to root, showing an increasing trend. The content of nitrogen atom percentage also had the same trend. (3) The cell wall ratio showed an increasing trend from the inside to outside and the height direction from the tip to root. 4) FTIR spectra corresponding to different heights were significant changes in 2 816−2 972 cm− 1, 1 651, 1 461 cm− 1 and 800−849 cm− 1. 1 700, 1 280 cm− 1 of the SDIR curve and 3 240−3 409 cm− 1, 2 921, 2 850 cm− 1, 1 619 cm− 1 of the 2DIR. The results indicated that the species and quantity of corresponding functional groups were correlated with the variation of straw height, it could infer changes of three kinds of basic units of straw.
ConclusionThrough the analysis of Micromorphology and functional groups of marigold straw, the corresponding relationship between radial size, internal structure, percentage of carbon and oxygen atoms, cell wall percentage and height direction of marigold straw were revealed. The variation of the types and quantities of functional groups contained in the main chemical constituents of straw in the direction of straw height was deduced.