Laccases: toward disentangling their diversity and functions in relation to soil organic matter cycling

Degradation of the recalcitrant polyphenolic plant residue lignin is a bottleneck of element turnover in terrestrial ecosystems. Consequently, there is a great interest to understand underlying mechanisms and dynamics, considering the possible ecological roles of soils as sinks or sources of carbon dioxide. The present review provides a critical, holistic view of the ecological importance of the degradation of recalcitrant residues attributed to laccase-producing soil microbes and laccase activity under different environmental conditions. We synthesize and discuss the results of previous classical ecological, enzymatic, and molecular-ecological studies to point out discrepancies between gene detection, enzyme activity, and substrate degradability. We single out major hindrances to current research and outline a progression toward a better understanding of laccase activity by fungi in soil ecosystems.