Nitrogen ecophysiology in trees of different functional groups of the Atlantic Forest (Southeastern Brazil): insights for urban forest restoration programs

Abstract

Background and aim The disorderly growth of cities has led to rapid transformation in urban environments, with indiscriminate land occupation causing drastic changes in city landscapes. In major cities like São Paulo, urban forests face numerous environmental stressors, including air pollution from carbon and nitrogen compounds. The vehicle fleet constitutes one of the main sources of emissions of these pollutants, accounting for approximately 10% of global greenhouse gas emissions. Given the extensive areas requiring restoration in cities and the promotion of forest restoration policies and actions in this decade (2021–2030), understanding patterns and processes inherent in the development of trees planted in urban forests is crucial. Thus, this study aimed to investigate intra-annual variations in N-NH₄⁺ and N-NO₃⁻ levels, as well as photosynthetic activity of young pioneer and non-pioneer trees from the Atlantic Forest planted in a highly anthropized environment, across different seasons of the year. Methods Four urban forest fragments with different land uses were selected in this study. Each location has a different impact of the automotive fleet on its surroundings and a different total area. Mixed soil samples at different depths were collected and subjected to chemical analysis for heavy metals. Results The results indicate that ecophysiological parameters of the analyzed species varied within predictable ranges but with significant particularities. Pioneer species exhibited differences in N-NH₄⁺ and N-NO₃⁻ utilization, as did non-pioneer species, which demonstrated greater niche breadth for some species. Regarding photosynthesis, seasonality significantly increased carbon assimilation in some taxonomic groups, while the functional group did not decisively define trends. Conclusion Newly planted species in highly impacted urban environments may develop different nitrogen (N) acquisition and metabolism strategies, influenced by seasonality in the deposition of nitrogenous pollutants from the atmosphere. This information should be considered in forest restoration plans in urban systems.