Nutrient addition increases insect herbivory in Nothofagus antarctica on North-Patagonian forests

Abstract

The change in nutrient availability in the soil can affect key functions of forest ecosystems, such as insect herbivory. Although insect herbivory is particularly relevant because it can impact on the growth and mortality of forest plant species, the evidence of the impacts of fertilizers addition on herbivory patterns is limited. In this study, we specifically evaluated how herbivory frequency on the timber species Nothofagus antarctica is affected by the addition of nitrogen (N), phosphorus (P), potassium (K) and their combinations to the soil, using a long term full-factorial field experiment in a North-Patagonian Forest (Argentina). Our study investigated the effects of fertilizers (N, P, and K) on herbivory frequency and leaf nutrient concentrations of the studied species. We found that the addition of fertilizers to the soil increased herbivory frequency, which was mediated by increases in leaf nutrient concentrations. Furthermore, we observed that interactions between fertilizers in leaf nutrient concentrations generally produced increases in herbivory, both in the amount of leaf consumed and in the foliar damage percentage. These findings suggest that fertilization can have complex effects on plant-herbivore interactions, and that the specific effects may depend on the identity of the nutrients that combined, the plant species, and the level of nutrient availability. Our results provide evidence that changes in soil nutrient availability are important in forest ecosystems, and that should be considered to develop effective management strategies for the sustainable use of natural resources in Patagonian forests.