Pollination benefits are maximized at intermediate nutrient levels

Yield production in flowering crops depends on both nutrient resource availability and pollination but their relative roles and potential interactions are poorly understood. We measured pollination benefits to yield in sunflower, combining a gradient in insect pollination (0, 25, 50, 100%) with a continuous gradient in nitrogen (N) fertilization (from 0 to 150 kg N ha-1) in an experiment under realistic soil field conditions. We found that pollination benefits to yield were maximized at intermediate levels of N availability, bolstering yield by a c. 25% compared to complete pollinator exclusion. Interestingly, we found little decrease in yield when insect visits were reduced by 50% indicating that the incremental contribution of pollination by insects to yield is greater when the baseline pollination service provision is very low. Our findings shed light on the processes that drive crop production, providing evidence for non-linear relationships between pollination and resource availabi...