Variation in δ15N enrichment in Cerrado fragments: edge effects and morphophysiology of Bauhinia holophylla

BACKGROUND AND AIMS: Large-scale agriculture has altered natural ecosystems, affecting nutrient availability for native plants. Nitrogen is often supplemented in the oligotrophic soils of the Cerrado with industrial fertilizers. Studies show that nitrogen can accumulate at the edges of native fragments near monocultures. However, research linking fragment size to nitrogen availability and plant physiological responses in Cerrado remains scarce. This study examined whether monocultures adjacent to Cerrado fragments introduce industrial nitrogen into conservation areas, and how it influences the physiological leaf traits of the native species, Bauhinia holophylla. METHODS: The study was conducted during the 2022 and 2023 rainy seasons, in Cerrado fragments (16-12,500 ha) adjacent to monocultures. Seven areas were sampled in 2022, with an additional area included in 2023. Sampling points were placed at fragment edges and interiors. Soil samples and B. holophylla leaves were analyzed for δ15N isotopic signature to compare enrichment between edges and interior. In the Panga Ecological Reserve (REP), functional leaf traits of B. holophylla leaves were assessed, including specific leaf area, relative water content, chlorophyll content, potential quantum yield (Fv/Fm), PSII quantum yield (ФPSII), fluorescence decline ratio (Rfd), and non-photochemical quenching (NPQ). KEY RESULTS: The soil and leaf δ15N values were higher at the edge than interior of the fragment. Although differences in δ15N values were observed among the fragments, there was no relationship with fragment size. Physiologically, B. holophylla individuals at the edges displayed higher specific leaf area and relative water content, whereas interior plants showed greater Rfd and NPQ. No differences were observed for chlorophyll content, Fv/Fm, and ФPSII. CONCLUSIONS: The findings suggest δ¹⁵N enrichment at the edges of the fragments due to industrial fertilizers. This nitrogen enrichment alters the leaf physiology of B. holophylla, indicating complementary adaptive strategies to maintain photosynthetic performance across different environmental conditions.