Significance: This study highlights previously unknown patterns of tree longevity and growth across the world. Tree-ring data reveal a large-scale trade-off between tree longevity and growth, following global patterns of increasing forest productivity and biomass turnover rate from temperate to tropical regions. The oldest known trees live under dry conditions in temperate and boreal zones, while in the dry tropical lowlands, trees only reach relatively short lifespans. Longevity of tropical trees also sharply decreases above mean annual temperatures of 25.4 °C. Thus, predicted future changes in moisture availability and increases in temperature have the potential to reduce tree longevity in tropical lowlands impacting carbon stocks.

Isotopes in tropical trees rings can improve our understanding of tree responses to climate. We assessed how climate and growing conditions affect tree-ring oxygen and carbon isotopes (δ¹⁸O_TR and δ¹³C_TR) in four Amazon trees. We analysed within-ring isotope variation for two terra firme (non-flooded) and two floodplain trees growing at sites with varying seasonality. We find distinct intra-annual patterns of δ¹⁸O_TR and δ¹³C_TR driven mostly by seasonal variation in weather and source water δ¹⁸O. Seasonal variation in isotopes was lowest for the tree growing under the wettest conditions. Tree ring cellulose isotope models based on existing theory reproduced well observed within-ring variation with possible contributions of both stomatal and mesophyll conductance to variation in δ¹³C_TR. Climate analysis reveal that terra firme δ¹⁸O_TR signals were related to basin-wide precipitation, indicating a source water δ¹⁸O influence, while floodplain trees recorded leaf enrichment effects related to local climate. Thus, intrinsically different processes (source water vs leaf enrichment) affect δ¹⁸O_TR in the two different species analysed. These differences are likely a result of both species-specific traits and of the contrasting growing conditions in the floodplains and terra firme environments. Simultaneous analysis of δ¹³C_TR and δ¹⁸O_TR supports this interpretation as it shows strongly similar intra-annual patterns for both isotopes in the floodplain trees arising from a common control by leaf stomatal conductance, while terra firme trees showed less covariation between the two isotopes. Our results are interesting from a plant physiological perspective and have implications for climate reconstructions as trees record intrinsically different processes.