Summary: Deposition of nutrients due to anthropogenic activities has the potential to change nutrient availability in nutrient‐limited ecosystems with consequences for plant and ecosystem processes. Species‐specific and ecosystem responses to the addition of nutrients were studied in a field experiment conducted in a Savanna (Cerrado sensu stricto) on dystrophic soil in central Brazil. Three fertilization treatments (N, P and N plus P additions) and unfertilized control were replicated in four 15 × 15 m plots per treatment. Five of the dominant woody species were studied. Specific leaf area (SLA) was not affected by the treatments, but species responded differently in terms of foliar nutrient concentration, resorption efficiency and proficiency to the increased soil N and P availability. Responses of N and P resorption suggested different levels of regulation for these two limiting elements, with a decrease in N and P resorption proficiency depending on the treatment. In general, under N fertilization, senesced leaves presented higher N concentration, whereas combined fertilization with N and P resulted in senesced leaves richer in P. The concomitant variation in P resorption efficiency and proficiency indicates a stronger regulation between them compared to N. Results indicated a highly efficient and complete P resorption, while N concentrations in senesced leaves indicated intermediate or incomplete resorption efficiencies, supporting the idea that Cerrado plants might be more limited by P than by N. At the ecosystem level, higher N concentration in the leaf litter was measured at the end of the dry season in the +NP‐fertilized plots, resulting in a significantly faster decomposition rate in relation to the control treatment. Responses of litterfall and decomposition rates indicated that the system was generally more responsive to the combined addition of N and P than to fertilization with N or P alone over the relatively short time span of this study.

Combined δ¹³C and δ¹⁸O analyses of leaf material were used to infer changes in photosynthetic capacity (A_max) and stomatal conductance (g_l) in Fagus sylvatica and Picea abies trees growing under natural and controlled conditions. Correlation between g_l and δ¹⁸O in leaf cellulose (δ¹⁸O_cel) allowed us to apply a semi‐quantitative model to infer g_l from δ¹⁸O_cel and also interpret variation in δ¹³C as reflecting variation in A_max. Extraction of leaf cellulose was necessary, because δ¹⁸O from leaf organic matter (δ¹⁸O_LOM) and δ¹⁸O_cel was not reliably correlated.In juvenile trees, the model predicted elevated carbon dioxide (CO₂) to reduce A_max in both species, whereas ozone (O₃) only affected beech by reducing CO₂ uptake via lowered g_l. In adult trees, A_max declined with decreasing light level as g_l was unchanged. O₃ did not significantly affect isotopic signatures in leaves of adult trees, reflecting the higher O₃ susceptibility of juvenile trees under controlled conditions. The isotopic analysis compared favourably to the performance of leaf gas exchange, underlining that the semi‐quantitative model approach provides a robust way to gather time‐integrated information on photosynthetic performance of trees under multi‐faced ecological scenarios, in particular when information needed for quantitative modelling is only scarcely available.