X-ray microdiffraction reveals the orientation of cellulose microfibrils and the size of cellulose crystallites in single Norway spruce tracheids

The microfibril angle (MFA) distribution and the size of cellulose crystallites in isolated double cell walls of Norway spruce (Picea abies [L.] Karst.) tracheids were determined by synchrotron X-ray microdiffraction using the reflections 200 and 004. Samples were 25 mu m thick longitudinal sections of earlywood from annual rings 6-18 of several stems. The asymmetric MFA distributions extended from -20 degrees to 90 degrees. The mean MFA of tangential cell walls decreased from an average of 24 degrees into 19 degrees from the pith to the bark. The mode of the MFA distribution was about 10 degrees smaller than the mean MFA. The standard deviation of the MFA distribution varied between 18 degrees and 25 degrees. The mean MFA and the mode of the MFA distribution were larger in radial than in tangential cell walls. MFA distributions of mature wood samples exhibited a separate small peak at around 90 degrees. The average width and length of cellulose crystallites varied between 28.9-30.9 angstrom and 192-284 angstrom, respectively. Both increased slightly as a function of annual ring number from the pith up to the 15th annual ring. An irrigation-fertilisation treatment of some of the stems resulted in longer cellulose crystallites compared to the untreated stems.