Decomposition of tobacco roots with modified phenylpropanoid content by fungi with contrasting lignocellulose degradation strategies

Abstract

The decomposition of tobacco roots with genetic modifications to lignin biosynthesis by the ligninolytic fungus Phanerochaete chrysosporium, by the cellulolytic fungus Chaetomium globosum, and by microbial communities in soil were examined to determine whether the rates of decomposition of the modified and unmodified roots decomposed at different rates, whether the order of colonization by P. chrysosporium and C. globosum facilitated decomposition, and whether the microbial community in soil was conditioned by exposure to roots subsequently so that the subsequent decomposition of the roots was increased. Both P. chrysosporium and C. globosum decomposed the modified roots more rapidly, at least initially, than the unmodified roots. Colonization by P. chrysosporium facilitated the subsequent decomposition by C. globosum, presumably because by degrading lignin, P. chrysosporium increased the susceptibility of the polysaccharide component of root material to attack by C. globosum. Selection of the soil microbial community by exposure to the modified residues accelerated subsequent decomposition of the root modified. Although demonstrating effects of the lignin modification on decomposition, they are relatively subtle and in most cases short-lived (less than 40 days) ones to which the microbial community is able to adapt, and therefore, we conclude that there are unlikely to be any persistent effects of the modified lignin on the soil decomposer community.