A global synthesis of below-ground carbon responses to biotic disturbance: a meta-analysis

Aim Climate change, especially the wider occurrence of extreme events, is likely to increase the intensity and frequency of insect/pathogen outbreaks (referred to as biotic disturbance), which may considerably affect plant ecophysiological traits and thus the ecosystem carbon (C) cycle. Little is known, however, about the ways in which biotic disturbance quantitatively affects ecosystem C processes, especially those that occur below ground. We reveal the general patterns of below-ground C responses to biotic disturbance from field manipulative experiments and opportunistic events. Location Global. Method We carried out a meta-analysis examining the effects of biotic disturbance on 16 variables associated with below-ground C processes, based on 64 experimental studies. Results Biotic disturbance significantly decreased below-ground C pools with relatively long residence times (e.g. root biomass and soil organic carbon, SOC), but increased labile C pools (e.g. microbial biomass carbon, MBC; dissolved organic carbon, DOC), soil respiration (Rs) and its components, and microbial population sizes. Compared with the neutral or positive effects of other environmental changes on below-ground C pools and fluxes, biotic disturbance had a negative effect on plant biomass and SOC but a larger positive effect on MBC, DOC and Rs. Main conclusions Biotic disturbance can have stronger impacts on below-ground C processes than other environmental changes, and the sensitive responses of soil labile C pools and C fluxes to biotic disturbance decrease long-term below-ground C sequestration. More research efforts are, however, needed to reduce the uncertainties in quantifying the effects of biotic disturbance and to improve forecasting of the feedback between the carbon cycle and climate.