Additive and synergistic effects of arbuscular mycorrhizal fungi, insect pollination and nutrient availability in a perennial fruit crop

Managing ecosystem services might reduce the dependence of modern agriculture on external inputs and increase the sustainability of agricultural production. Insect pollinators and arbuscular mycorrhizal fungi (AMF) provide vital ecosystem services for crop production, but it has not been tested whether their effects on crop yield interact and how their effects are influenced by nutrient availability. Here we manipulated insect pollination, AMF inoculation and fertilizer application (four levels) in a randomized complete block design with potted raspberry (Rubus idaeus L.) to assess the interacting effects of these variables on crop yield. AMF inoculation increased the per-plant flower number by 33% and the fruit number by 35%, independently from insect pollination and fertilizer application. Single berry weight furthermore increased more strongly with fertilizer application rates in AMF inoculated plants than in non-inoculated plants. As a consequence, AMF inoculation boosted raspberry yield by 43% compared to non-inoculated plants. AMF inoculation increased pollinator visitation rate per plant under intermediate fertilizer levels, suggesting additional indirect effects of AMF inoculation on yield. Fruit yield of pollinated plants increased more strongly with fertilizer application rate than the yield of plants from which pollinators had been excluded. At maximum nutrient availability, the combined benefits of both ecosystem services resulted in a 135% higher yield than that of fertilizer-only treatments. Our results suggest that the benefits of ecosystem services on yield can be additive or synergistic to the effects of conventional management practices. Intensive, high-input farming systems that do not consider the potential adverse effects of management on ecosystem service providing species might risk becoming limited by delivery of ecosystem services. Proactively managing ecosystem services, on the other hand, has the potential to increase crop yield at the same level of external inputs.