Augusto Cesar Franco

Increasingly frequent and intense drought events are challenging the survival of several forest species worldwide. Yet, the extent to which plants can postpone drought-induced mortality (DIM) through plastic adjustments in traits linked to hydraulic failure (HF) remains unclear. Here, we explored how the coordinated drought-induced plasticity in traits controlling water loss (WL), water storage capacity (WS), and drought tolerance (DT) influences the time to HF in a group of representative Cerrado species. Long-term exposure to drought induced marked morphoanatomical alterations in all the studied species, which minimized the impairments to their growth, while simultaneously reducing the risk of HF. However, those changes occurred almost exclusively in traits associated with the control of WL, both before and after complete stomatal closure, whereas traits related to WS and DT exhibited limited phenotypic plasticity. Despite this limited plasticity in hydraulic traits, all species showed inherently high hydraulic safety margins, achieved through a combination of early stomatal closure and high resistance to embolism, probably reflecting evolutionary pressures imposed by recurrent seasonal droughts in the Cerrado. Overall, our results highlight the need to embrace the complexity of drought acclimation mechanisms to improve the predictions of plant performance and survival under extreme weather events.

Trees of southern Amazonian forests face an increase in the duration and intensity of soil and atmospheric drought, which impose a higher risk of hydraulic failure in the water transport system, decreasing the water supply to foliage and increasing the risk of dehydration and death. However, it is not well understood how key hydraulic‐related traits vary among southern Amazonian forests and whether Amazonian trees adjust them to be more drought tolerant along a gradient of increasing aridity. We measured leaf water potential (Ψ _leaf ) in the dry season, xylem water potential associated with 50% (Ψ ₅₀ ) and 88% embolism formation, hydraulic safety margin (HSM ₅₀ ) and wood density (WD) in four forests at the southern edge of the Amazon. We compared our results with measurements from the literature for 10 additional forests distributed across the Amazon and subjected to different maximum cumulative water deficit (MCWD), a climate index for drought severity. For some analyses, species sampled within each forest were weighted by basal area to obtain community‐weighted means (CWMs). Southern edge forests had high resistance to hydraulic failure, with more negative Ψ ₅₀ than other Amazonian forests. HSM ₅₀ across species correlated positively with predawn Ψ _leaf , suggesting that shallower rooting species in these forests face greater risk of hydraulic failure. Across all sites considered (southern and wider Amazon), HSM _{50_CWM} did not correlate with MCWD, despite a more negative Ψ _{50_CWM} with increasing MCWD. However, forests at the driest range of MCWD showed greater variability in hydraulic failure risk and contained more species potentially operating beyond their hydraulic limits. Synthesis . Although southern Amazonian forest species have undergone selection for high hydraulic resistance, they are not equally safe to hydraulic failure, highlighting the importance of site‐ and species‐dependent factors. On a broader scale across the Amazon, tree communities in drier sites maintain HSM _{50_CWM} similar to those in wetter sites. This may be the result of species turnover towards taxa with more negative Ψ ₅₀ or shifts in water use strategies, such as tight stomatal regulation, deeper rooting or seasonal leaf shedding.

The rapid spread of non-native perennial grasses across South American savannas poses a growing threat to native plant diversity and ecosystem functioning. They disrupt key ecological processes, including fire regimes, nutrient cycling and plant community dynamics, driving the loss of functional diversity and the homogenization of native vegetation. This review compiles current knowledge on the ecological impacts of the nine most invasive perennial grass species in South American savannas and the challenges faced in controlling them, with a particular emphasis on the Brazilian Cerrado. We examine the mechanisms by which they outcompete native species, alter soil–plant interactions and inhibit natural regeneration. Particular attention is given to the ecological traits that confer competitive advantages to these invasive grasses under conditions of disturbance, increased nutrient availability and climate change. We also evaluate the challenges faced in the ecological restoration of invaded areas and discuss integrated strategies for controlling invasions and promoting the recovery of native species. This synthesis underscores the urgent need to address invasions by non-native grasses through coordinated research, new policies and management efforts aimed to safeguard the long-term biodiversity and ecological resilience of South American savannas.

Over the past 5000 years, the predictable climate seasonality of the Brazilian Cerrado has played a crucial role in shaping the life history strategies of species and the structure of ecological communities of this global biodiversity hotspot. However, this biome is becoming hotter and drier, with a notable lengthening and intensification of the dry season. Declining rainfall results from three key factors: the expansion of the South Atlantic Subtropical Anticyclone, warming of northern tropical Atlantic waters, and reduced evapotranspiration during the dry season due to widespread land conversion. The evapotranspiration drop also plays a pivotal role in regional warming and higher vapor pressure deficit. Climatic change already affects the physiology, phenology, and reproduction of the Cerrado plants, while also driving community‐level alterations, such as woody encroachment and ant–plant–herbivore interaction outcomes. Dry season lengthening is likely to reduce the biomass and alter the dynamics of microbial communities, with negative effects also extending to invertebrates and other groups. The pronounced warming reduces the amount and duration of dewfall, an important water source for insect pollinators and other animals with low vagility during periods of drought. Concerning vertebrates, the most suggested impact is the loss of specialist or endemic species, with restricted distributions, and the expansion of generalist species, lowering the levels of β‐ and γ‐diversity across the region and making communities poorer and more homogenized. In summary, climate change is actively reshaping Cerrado communities, and species' survival will largely depend on their phenotypic plasticity, evolutionary response, and dispersal capabilities. This article is categorized under: Assessing Impacts of Climate Change > Observed Impacts of Climate Change Climate, Ecology, and Conservation > Observed Ecological Changes Trans‐disciplinary Perspectives > Regional Reviews

Seeds of many Amazonian floodplain forest trees are dispersed during high-water periods and spend weeks or months underwater until the flooding retreats. To assess whether prolonged seed submersion affects germination and early seedling development, an experiment was carried out in a greenhouse with seeds of Campsiandra laurifolia, Cassia leiandra, Crataeva tapia, Ilex inundata, Macrolobium acaciifolium, Nectandra amazonum, Pouteria glomerata, Psidium acutangulum, Sorocea duckei, and Vitex cymosa. They are common in this type of forest, differ in fruit type, number of seeds per fruit, fruit dimensions, and fresh mass and have fruits or seeds that can float. Seeds were collected in a Central Amazonian floodplain forest (flooded approximately 6 months year⁻¹; water column of 5 m) and germinated in (1) irrigated soil or (2) underwater (water column of 5–7 cm) for 6 months. Seeds that germinated underwater were transferred to drained soil. Seeds of all species germinated underwater and developed seedlings when transferred to soil. However, submersion reduced the germination percentage of Psidium acutangulum, N. amazonum, P. glomerata and V. cymosa. Six species delayed germination in water. Ca. leiandra, I. inundata and P. glomerata did not differ in mean germination time in drained soil and underwater, whereas S. duckei seeds germinated faster underwater. Seed submersion negatively affected seedling growth (shoot length) of three species but did not affect seedling biomass. Timing of fruit dispersal, fruit buoyancy and high number of seeds per fruit can be critical for species with seeds that are not as able to cope with long-term submersion.

Fatty acids (FAs) stored as triacylglycerols (TAGs) are an important source of carbon and energy for germination and seedling development, particularly for plants with small wind-dispersed seeds, allowing greater efficiency in storing both energy and carbon. These plants should be under strong selection to produce seeds rich in FAs and with large amounts of saturated FAs. Their closely packed single-chain configuration allows greater packing, more carbon and energy per unit mass, and are less costly to produce. Efficient carbon storage would be less crucial for zoochorous species, which can reach much larger seed sizes (mass). We analyzed the transesterified fatty acid profile from seeds of 22 anemochorous and zoochorous tree species from the Cerrado savannas of Central Brazil. We tested if seed FA content covaried with seed mass and if anemochorous and zoochorous seeds differed in FA contents and distribution. Fatty acids were an important seed source of carbon and energy for most species. Fifteen different FAs were identified. Oleic, linoleic and linolenic tended to be the predominant unsaturated FAs. Oleic acid corresponded to more than 60% of the total transesterified FAs in seeds of Kielmeyera coriacea, Qualea dichotoma and Triplaris americana. Linoleic acid corresponded to more than 50% of total FA in Dalbergia miscolobium, Parkia platycephala and Ferdinandusa elliptica while linolenic acid was the dominant component in Inga cylindrica. Across species, palmitic and stearic were the dominant saturated FAs. The only exception was lauric acid (68% of total FA) in seeds of Qualea grandiflora. On a log₁₀ scale, as the seed increased in mass, accumulation of FAs tend to proceed at a faster rate in anemochorous species than in zoochorous species. They also became increasingly richer in saturated FAs. Zoochorous species had seed TAGs with higher proportion of polyunsaturated fatty acids

Context: Arundo donax L. is an exotic, perennial grass that has invaded dryland and wetland savannas of central Brazil. This species produces sterile flowers in its introduced range and propagates vegetatively via rhizomes and stem fragments. Aims: We investigated bud sprouting capacity after fragmentation, which plays a major role in plant-proliferation ability, invasiveness and its escape from weed-control measures. Methods: We evaluated the effects of size, different periods of desiccation (by exposure to air), submersion and water-column height on the regenerative capacity of single-node stem fragments. Key results: Fragments of a minimum size of 3–4 cm successfully regenerated new plants. The regenerative capacity of single-node stem fragments (3–10 cm length) rapidly decreased after 1 week of air desiccation. Stem fragments that were submerged for 30 days resprouted and formed plants in a water column of 5, 10 or 15 cm, with no significant difference from the controls. However, leaves did not expand and shoot elongation was adversely affected in 15 cm of non-aerated water. This loss of performance was reversed when the newly formed plants were removed from the water and transferred to a moist substrate. Implications: Our findings suggest that weed management, which involves cutting the plant to ground level without removing it from the site, is inefficient and can intensify the potential for invasion by A. donax, especially in the rainy season, when left-over stem fragments remain hydrated and capable of regeneration. Its establishment near riverbanks must be monitored because submerged propagules remain viable and able to resprout.

Fire–vegetation feedbacks potentially maintain global savanna and forest distributions. Accordingly, vegetation in savanna and forest ecosystems should have differential responses to fire, but fire response data for herbaceous vegetation have yet to be synthesized across biomes. Here, we examined herbaceous vegetation responses to experimental fire at 30 sites spanning four continents. Across a variety of metrics, herbaceous vegetation increased in abundance where fire was applied, with larger responses to fire in wetter and in cooler and/or less seasonal systems. Compared to forests, savannas were associated with a 4.8 (±0.4) times larger difference in herbaceous vegetation abundance for burned versus unburned plots. In particular, grass cover decreased with fire exclusion in savannas, largely via decreases in C₄ grass cover, whereas changes in fire frequency had a relatively weak effect on grass cover in forests. These differential responses underscore the importance of fire for maintaining the vegetation structure of savannas and forests.