Plants increase laccase activity in soil with long-term elevated CO2 legacy

• We assessed effects of plant presence and elevated CO2 on laccase activity.
• Plants enhanced laccase activity in the soil.
• Laccase stimulation was largest in soil exposed to long-term elevated CO2 treatment.
• Short-term (6 months) elevated CO2 exposure did not affect laccase activity.

Actively growing plants can stimulate mineralization of recalcitrant soil organic matter (SOM), and increased atmospheric [CO2] can further enhance such plant-mediated SOM degradation. Laccases are central for recalcitrant SOM decomposition, and we therefore hypothesized that plants and elevated [CO2] stimulate laccase activity. We incubated soil exposed to seven years of elevated or ambient field [CO2] in ambient or elevated [CO2] chambers for six months either with or without plants (Deschampsia flexuosa). Elevated chamber [CO2] increased D. flexuosa production and belowground respiration. Interestingly, plants also grew larger in soil with an elevated [CO2] legacy. Plants stimulated soil microbial biomass, belowground respiration and laccase activity, and the plant-induced laccase stimulation was particularly apparent in soil exposed to long-term elevated [CO2] in the field, whereas laccase activity was unaffected by short-term chamber [CO2]. Hence, actively growing plants can stimulate laccase activity, but the potential for plant-induced laccase production appears to depend on the laccase production potential of the soil. Further, initial differences in laccase production potential prevailed during the six months experimental period independent of current [CO2], although plant production increased at elevated [CO2] during this period. Taken together, these findings suggest that although laccase activity depends on plant presence, the laccase production potential does not respond fast to increased plant production.