Lignin decomposes slowly due to:
Lignin decomposes slowly because it is a heterogeneous, cross-linked aromatic polymer with irregular bonds rather than a repeating structure readily attacked by common hydrolases. It encrusts cellulose in secondary cell walls, reducing enzyme access to otherwise degradable carbohydrates. A limited set of fungi and bacteria produce oxidative enzymes such as lignin peroxidase, manganese peroxidase, and laccase, and these reactions are energetically costly. High protein would generally improve substrate quality, whereas structural complexity and chemical recalcitrance prolong persistence. Environ
Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 3
