Weight-length relationships of coniferous wood tracheid skeletons
Creators: name: Sastry, Cherla Bhaskararama
Publisher: name: University of British Columbia
Year: 2011

description: The hypothesis is examined that, among individual tracheids of coniferous woods, the weights of holocellulose and alpha-cellulose skeletons are a direct quantitative function of their length, independent of species. A total of 28 annual increments, representing wood from nine coniferous genera and seven families, separated into earlywood and latewood fractions, was delignified with peracetic acid and subsequent reduction with NaBH₄. Further reduction to alpha-cellulose followed for a portion of the holocullulose skeletons. About 750 individual holo- and alpha-cellulose tracheid skeletons were measured for length and weight. A specially developed quartz ultra micro-balance, having a weighing range of 0.06 to 14 μg and a precision ± 0.03 μg, was constructed and used to weigh; individual tracheids. Statistical analyses indicated a significant positive curvilinear relationship between length of tracheid and weight of its carbohydrate fraction. Estimated variations accounted for in holocellulose and alpha-cellulose skeleton weights, by the length factor alone were, respectively, 91.9 and 95.7 per cent for pooled data of all the species. No significant differences in holocellulose skeleton weights were evident within species for the same tracheid length, whereas weights of alpha-cellulose skeletons within species, and both the holo- and alpha-cellulose between species, differed significantly. Radial variation for single tracheid weights followed trends similar to those established by others for specific gravity, and percentage of cellulose based on gross wood analyses. Individual tracheids of juvenile wood had significantly lower (1% level) alpha-cellulose skeleton weights than those from mature and overmature wood, while differences were nonsignificant for holocellulose. Overmature wood tracheids were significantly lighter (carbohydrate skeleton weight) than those from mature wood, for the same tracheid length. Differences between earlywood and latewood were explored. For the same tracheid length, both earlywood and latewood tracheids contained similar amounts of alpha-cellulose, whereas the amount of holocellulose per tracheid was higher in latewood. Examination of compression wood also provided positive evidence for the length-weight relationship in tracheids. When weights of compression wood tracheids were compared with those of regular (normal) wood, no significant differences were apparent for holocellulose tracheid skeletons, whereas significant differences were found for alpha-cellulose. It was concluded that, for the same tracheid length, compression wood tracheids may have a lower amount of alpha-cellulose than those from mature (normal) wood, but a higher amount than those from juvenile wood. Changes in Douglas-fir tracheid weights were studied in wood formed before and following tree fertilization. Variations, for the most part, were found to be associated with changes in tracheid length. Qualitative differences attributable to treatment composition (Urea vs. NPK vs. (NH₄)₂SO₄) were also noted, in that some treatments resulted in less weight of alpha-cellulose per unit length of tracheid, when compared with normal wood tracheids. This reduction in cellulose fraction was suggested as a possible factor for differences observed in gross wood specific gravity in wood of some fertilized trees. Results were compatible with the proposed hypothesis.