Laccase and Tyrosinase Activities Reveal Contrasting Responses Associated with Soil C and N Pools Across Italian Land-Use Systems

Purpose Soil oxidative enzymes play a key role in the transformation of complex organic compounds and the regulation of soil organic matter (SOM) dynamics. This study investigated laccase and tyrosinase activities across five Italian sites representing contrasting land-use systems and management regimes. Methods Enzyme activities were evaluated in relation to soil pH, soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon (DOC), total dissolved nitrogen (TDN), and C:N stoichiometric ratios. Results Soil biochemical variability was primarily structured by site, whereas management effects were evident mainly where contrasting practices substantially altered C and N availability and substrate inputs. Laccase and tyrosinase displayed contrasting responses to soil C and N gradients. Laccase activity was positively associated with DOC and the DOC:TDN ratio and decreased with increasing pH, whereas tyrosinase increased with TDN and pH and was negatively associated with SOC:TN and DOC:TDN. These relationships suggest that the two enzymes were associated with distinct oxidative pathways involved in SOM transformation. Stoichiometric indicators were associated with broad-scale variability in enzyme activity across contrasting sites, but their predictive power was weaker within individual sites, where the narrower range of C variation may increase the relative importance of local factors. Management effects were mostly evident in the tomato system, where conventional, organic, and agroecological practices altered the relationships between oxidative enzymes and C:N ratios. Conclusion The findings highlighted the functional divergence between laccase and tyrosinase and support their combined assessment, together with soil C and N pools, as complementary indicators of SOM transformation across contrasting land-use systems.