Leaf quality and herbivory responses to soil nutrient addition in secondary tropical dry forests of Yucatan, Mexico

Leaf quality (nutrient concentration) and herbivory were studied in a set of dominant tree species in regenerating, secondary tropical dry forests growing on limestone in the Yucatan Peninsula. The study's objective was to assess how variation in nutrient availability affects leaf nitrogen and phosphorus concentrations and herbivory. Our study included an area of young forest (10 y old), with phosphorus-poor soils, and an area of old forest (similar to60 y old), in which soil P was comparatively less limiting. The foliage of representative species of each site was studied, including Acacia gaumeri, Leucaena leucocephala and Lysiloma latisiliquum at the young forest site, and A. gaumeri, Bursera simaruba and Pithecellobium dulce at the old forest. Four independent plots (12 x 12 m) at each forest were either left intact (controls) or fertilized with N, with P, or with N plus P for three consecutive years. Relaxation of nutrient limitations at the young forest resulted in an increase in leaf phosphorus and herbivory in all species. In contrast, N and P fertilization at the old forest site did not consistently affect leaf nutrient concentration and leaf damage. In this site the main response to fertilization was an increase in leaf nitrogen only in B. simaruba and an increase in herbivory in A. gaumeri; leaf phosphorus was unaffected by soil fertilization. Overall, we observed that, subsequent to nutrient addition, leaf phosphorus concentration and herbivory in the leguminous species increased at the young site; leaf nitrogen concentration in the non-leguminous species increased at the old site while herbivory only increased in A. gaumeri, following a pattern similar to that observed in the young site. We conclude that the regulatory mechanisms of leaf quality and damage by herbivores will vary, depending on the details of the site's nutrient limitations and the identity of species.