Preparation of Specifically Labeled 14 C-(Lignin)- and 14 C-(Cellulose)-Lignocelluloses and Their Decomposition by the Microflora of Soil

Abstract

Microbial decomposition of lignocellulose in soil was studied using radioisotope techniques. Natural lignocelluloses containing ¹⁴C in either their lignin or cellulose (glucan) components were prepared by feeding plants l-[U-¹⁴C]phenylalanine or d-[U-¹⁴C]glucose, respectively, through their cut stems. Detailed chemical and chromatographic characterization of labeled lignocelluloses from three hardwood and three softwood species showed that those labeled by the [¹⁴C]glucose incorporation method contained specifically labeled cellulosic components, whereas those labeled by the [¹⁴C]phenylalanine incorporation method contained specifically labeled lignin components. Microbial degradation of these differentially labeled lignocelluloses was followed by monitoring ¹⁴CO₂ evolution from selected soil samples incubated with known amounts of radiolabeled lignocelluloses. The lignin components of the six woods were shown to be decomposed in soil 4 to 10 times more slowly than their cellulosic components. These rates of mineralization were comparable to the generalized patterns previously reported in the literature. The present technique, however, was thought to be simpler, more sensitive, and less prone to interference than methods previously available.