Growth and physiological responses of Atlantic Forest tree seedlings to nitrogen and phosphorus addition.

Key Message: Atlantic Forest tree seedlings with contrasting ecological characteristics present specific growth and physiological responses to nitrogen and phosphorus addition in the soil. Nitrogen (N) and phosphorus (P) are commonly the most limiting nutrients for plant growth in tropical forests. Many of these ecosystems are exposed to increasing rates of anthropogenic nutrient deposition. This study aims to assess how five Atlantic Forest tree species respond to N and P addition to the soil. Five species with different levels of shade tolerance were subjected to nine weekly soil applications of (NH₄)₂SO₄ (84 kg N ha⁻¹ treatment N), NaH₂PO₄ (45 kg P ha⁻¹ treatment P), both nutrients (treatment N + P), or water. Soil, foliar nutrient concentrations, and biometric and gas exchange analyses were performed. No changes in the soil pH or total N and P availability were observed in the soil after N addition, whereas P accumulated in the soil and leaves of three species after P addition. The pioneer species H. popayanensis presented increased total biomass with P and N+P treatments, while C. floribundus increased with P treatment and C. pachystachya increased with N + P treatment. N and P treatments reduced the photosynthesis of C. pachystachya and the stomatal conductance of C. pachystachya and C. floribundus. The growth rate and total biomass of C. estrellensis reduced with N and P treatments and increased with N+P treatment. Aspidosperma polyneuron presented reduced photosynthesis with N treatment, but increased total biomass with all treatments, especially N + P. The diversity of growth and physiological responses to N and P addition suggests that each species has specific nutrient requirements and uses strategies related to the niche occupied by each one. [ABSTRACT FROM AUTHOR]