Leaf water potential is a good indicator of tree species responses to rainfall seasonality, allowing to better understand water stress effects on vegetation. We investigated daily and seasonal patterns on leaf water potentials of 21 dominant species in three distinct vegetation types from the Cerrado-Amazonia transition to assess how they respond to seasonal changes in water availability. We found that the variation on leaf water potential (Ψl) across species was higher in the dry compared to the rainy season, for all vegetation types. Typical cerrado and cerradão species showed similar patterns, with higher Ψl regulation under higher VPD and lower variation in predawn Ψl (ΔΨpd), indicating root access to soil water even during intense drought. In contrast, seasonal forest species showed lower regulation under lower VPD effects in both seasons, and higher ΔΨpd, indicating lower access to deep water in the soil. These differences revealed two main groups of species: higher Ψl regulators with a strategy isohydric occurring in both typical cerrado (savannah) and cerradão (woodland), and lower Ψl regulators with anisohydric strategy, occurring in seasonal forest. Our results suggest that seasonal tropical forest species will become very vulnerable to predicted increases on drought severity in the region.

Aims: Amidst the Campos the Altitude (Highland Grasslands) in the Brazilian Atlantic Forest, woody communities grow either clustered in tree islands or interspersed within the herbaceous matrix. The functional ecology, diversity and biotic processes shaping these communities are largely unstudied. We characterised the functional assembly and diversity of these tropical montane woody communities and investigated how those communities fit within the Grime’s CSR (C – competitor, S – stress-tolerant, R – ruderal) scheme, what trade-offs they exhibit and how traits and functional diversity vary in response to bamboo invasion. Methods: We sampled five leaf traits and wood density along transects covering the woody communities both inside tree islands and outside (i.e. woody plants in the grasslands community) to characterise the functional ecology of the community. We used Kruskal-Wallis test, t-test and variation partitioning to determine effects of inside vs outside the tree island and bamboo invasion on traits, woody species diversity and functional diversity. Results: We found a general SC/S strategy with drought-related functional trade-offs. Woody plants in tree islands had more acquisitive traits, whereas woody plants within the grasslands had more conservative traits. Trait variation was mostly taxonomically driven, and species composition varied between inside and outside tree islands. Leaf thickness, wood density and foliar water uptake were unrelated to CSR-strategies, suggesting independent trait dimensions and multiple drought-coping strategies within the predominant S-strategy. Bamboo-invaded islands showed lower Simpson diversity, lower functional dispersion, lower foliar water uptake and greater leaf thickness than non-invaded tree islands. Conclusions: The observed functional assembly in response to bamboo and facilitation have implications for future forest expansion and response of the communities to climate change. Further studies on eco-physiological and establishment traits and the mechanisms behind biotic interactions are needed to better understand the response of these communities to future environmental changes.