Soil Fertility and Leaf Traits Drive Insect Herbivory Variation Across a Tropical Grassland-Savanna-Forest Gradient

Abstract

Question: Understanding the interplay between plant functional traits and abiotic factors in shaping observed differences in herbivory across broad environmental gradients remains a central challenge in plant community ecology. We assessed the relative contributions of environmental factors, such as soil properties and nutrient availability, and leaf functional traits in governing insect herbivory levels across a tropical grassland-savanna-forest gradient. Location: Espinhaço Range, southeastern Brazil. Methods: We sampled soils and leaf functional traits in 72 species from 30 families in campo rupestre grassland, cerrado, and gallery forests during the end of the rainy season. Our design provides a useful model to study herbivory along environmental gradients because it accounts for and corrects for variations in climate, latitude, and elevation. In each site, 2500 sampled leaves were collected, pressed, oven-dried at 70°C for 72 h, and scanned to obtain the percentage of leaf area removed by chewing insects. Results: Grassland species showed the lowest SLA values, followed by the cerrado, while forest plants had the highest values. SLA correlated positively with soil fertility (PC1: high soil N, P, organic matter, and cation-exchange capacity) and negatively with PC2 (associated with lower Ca and base saturation). Consistently, forest plants showed higher insect herbivory compared to those from the cerrado and the grassland, and herbivory levels were also correlated with soil characteristics. Conclusions: Among-habitat differences highlight the influence of soil fertility on plant functional traits and herbivory levels, indicating that plants on more fertile soils, such as in forests, are more likely to grow fast but also experience higher levels of herbivory compared to those in less fertile environments. This relationship underscores the importance of considering soil fertility in studies of plant–herbivore interactions and highlights the role of environmental gradients in shaping these dynamics.