Leaf non-structural carbohydrates dominantly drive background insect herbivory of temperate tree species in Northeast China

Abstract Herbivorous insects shape plant growth and community assembly, while conversely, plant traits, especially leaf traits, profoundly affect herbivore behaviors. However, which leaf traits and how they dominantly drive insect herbivory in a natural forest habitat remain undefined. In this study, we evaluated the background insect herbivory of 45 individual trees from five broadleaved tree species in the northeast of China. Based on that, 17 leaf traits representing four groups—leaf structural traits, photosynthetic pigments, nutrient traits, and secondary metabolites—were measured. Finally, the correlation between 17 leaf traits and background insect herbivory was investigated. The results indicated that the damaged leaf area (DLA) exhibited positive correlations with leaf structural traits (leaf mass per area and leaf size) and nutrient traits (soluble sugar (SS), non-structural carbohydrates (NSC), SS/NSC), and a negative correlation with photosynthetic pigments, nitrogen/phosphorus ratio, and anthocyanins. Meanwhile, SS/NSC, SS, leaf size, total phenol, and phosphorus were identified as the five relatively important leaf traits contributing to DLA by the quantitative estimation based on SHAP (SHapley Additive exPlanations) values. Furthermore, nutrient traits accounted for 52.9% of DLA explanation, showing the most important group of leaf traits. In addition, structural traits and secondary metabolites were found to interactively influence herbivory. These findings provide valuable insights into the complex interactions between host plants and herbivorous insects in forest ecosystems.