Estimation and comparison of acid detergent lignin and acetyl bromide lignin in fallen leaves using near-infrared spectroscopy
Several analytical methods have been developed to measure the lignin content corresponding to different plant species and different regions. The sulphuric acid method is commonly used for objective determinations of lignin content using near-infrared spectroscopy. Lignin is a complex polymer of lignin units. The types and ratios of lignin units vary among taxonomic classes of plants. To compare the lignin content as determined by different methods of chemical analysis, fallen leaves of different species were analysed using both the acid detergent and acetyl bromide procedures. Near-infrared reflectance spectra were obtained for each sample of dried ground leaves, and stepwise multiple linear regression analyses were performed to compare the amounts of lignin determined using acid detergent and acetyl bromide. In monocotyledonous herbaceous plants, the lignin content determined by acetyl bromide was more than twice that determined by acid detergent. Despite the difference in the values, regression analysis provided acceptable results for both lignin preparations. Although the acid detergent procedure has generally been regarded as accurate for lignin determination, our results suggest that caution is required in the selection of the method of chemical analysis when using near-infrared spectroscopy to estimate the lignin content of different taxonomic classes of plants.