Near-infrared reflectance spectroscopy for the determination of lignin-derived compounds in the decomposed and humified litters of coniferous and deciduous temperate forests in Northern Kanto District, Central Japan

Abstract

Methods to determine the contents of lignin-derived compounds in decomposed or humified forest litter often involve time-consuming physical and chemical analyses. In this study, a rapid and accurate method with minimal pre-treatments was developed to determine the contents of recalcitrant lignin-derived compounds in decomposed or humified litter on a forest floor using near-infrared reflectance spectroscopy (NIR) and partial least square (PLS) regression analysis. We prepared and quantitatively and spectrophotometrically analyzed 92 litter samples obtained in a litter decomposition experiment at three sites, the Tsukuba Experimental Site, the Tengakura Experimental Site and the Ogawa Forest Reserve, all of which are located in the northern Kanto District of central Japan. The NIR equations to determine the respective lignin-derived compounds at the three sites were developed by PLS regression using quantitative and spectrophotometrical data. The NIR models developed to determine the compositional properties of decomposed and humified litter were extremely accurate compared with the results of previous published studies using stepwise multiple linear regressions. We believe that the NIR equation developed in the present study has the potential to be applicable to qualifying the determination of soil organic matter (SOM) in the SOM-rich surface soil of the forests around the northern Kanto District because lignin-derived compounds can be determined by NIR in samples with a large diversity of compositional ranges and litter decomposition stages.