Como a suplementação de nitrogênio e fósforo pode alterar a fisiologia de plantas nativas do Cerrado?

Abstract

Human activities have globally modified the cycle of essential nutrients for plants, potentially affecting the physiology of native species. In South America, specifically in the Brazilian Cerrado, large areas have been transformed into agricultural lands over time. Due to the oligotrophic conditions of the biome, the use of industrial fertilizers is widely adopted to provide ideal conditions for the growth and development of cultivated plants. In general, among the essential mineral nutrients, nitrogen is the most required in quantity by plants. Consequently, the concentration of this element has increased over the years in natural ecosystems near monocultures that use nitrogen fertilizers. Due to surface runoff, leaching, and volatilization, part of the nitrogen may reach higher concentrations, especially at the edges of remaining natural ecosystems. This can influence not only the dynamics of nitrogen in the soil and plants but also the availability of carbon. Non-radioactive stable isotopes of 15N and 13C have been used in ecological studies to determine the origin and transport of N and C in natural environments. In the first chapter, the presence of 15N in the soil and leaves of a Cerrado plant species was examined at the interior and edges of eight Cerrado fragments was verified, along with 15N in the leaves of Bauhinia holophylla over two years. The relationships between 15N and 13C the edges and interior of the fragments were also analyzed. Intermediate Cerrado fragments showed higher values of 15N in the leaves at the edges. In one of the fragments where 15N was higher at the edge, the physiology of B. holophylla was analyzed, revealing higher values of specific leaf area (SLA) and relative water content (RWC) at the edges. On the other hand, the results of photosynthesis suggest that, inside the fragment, plants have a greater capacity to dissipate excess light energy and maintain a more preserved photosynthetic apparatus, which may indicate stress at the edges. In the second chapter, N, P, and N+P supplementation was applied to 25 permanent plots of 100m² each, and the physiological effects of B. holophylla were analyzed. The specie showed an increase in SLA and RWC in the treatment with N+P supplementation, while the potential quantum yield (Fv/Fm) was higher in the treatment with P supplementation alone. On the other hand, P supplementation showed lower capacity to dissipate excess light energy and less protection against excess light. The third chapter addressed the physiological responses to supplementation with N, P, or N+P in Handroanthus impetiginosus (Mart. ex DC.) grown in a greenhouse. Supplementation with N or P promoted an increase in leaf area and growth, while the combination of N+P increased leaf efficiency for light capture. However, in the combined supplementation of high N+P (2.44 g of N and 2.50 g of P), the plants did not show changes in total size and of chlorophyll fluorescence and exhibited decreased photosynthetic efficiency and stomatal conductance. These results indicate that high availability of N+P may compromise the physiological heath of H. impetiginosus.