Anthropogenic deposition increases nitrogen-phosphorus imbalances in tree vegetation, litter and soil of Atlantic Forest remnants

Aims Increased N deposition may cause nutritional imbalances in tropical ecosystems, by shifting N:P stoichiometry (as they are typically P-limited) and NH4-N:NO3-N ratios throughout their compartments. Based on this assumption, we aimed at verifying if the anthropogenic N deposition are inducing nutritional imbalances in trees, litter and soil in the remaining Atlantic Forest in SE Brazil. Methods Three forest remnants were selected, one of them supposedly exposed to lower levels anthropogenic N deposition (peri-urban forest) than the other two (urban and agricultural-urban forests). We measured NO2 concentrations, wet and dry deposition of NH4-N, NO3-N and PO4-P and determined total/soluble N and P contents in samples of pioneer and non-pioneer trees, litter and soil. NH4-N:NO3-N and N:P ratios were calculated in all compartments. Results Multivariate analysis indicated associations between NH4-N, PO4-P and NH4:NO3 ratios in atmospheric deposition or NO2 concentrations and N and P contents in trees, litter and soil of all forest remnants. The comparison of N:P ratios in tree species and litter with those from studies conducted in the 1980-2000 indicated a tendency of N enrichment and increasing P scarcity in the Atlantic Forest remnants studied. Conclusions Confirming the hypothesis, anthropogenic N deposition increases nutritional imbalances in the ecosystem compartments of forest remnants studied. The peri-urban forest showed to be more vulnerable to nutritional imbalances than the other forests, based on the comparisons with data from 30 to 40 years ago. (AU)