Summary: Drought stress selects for a suite of plant traits at root, stem and leaf level. Two strategies are proposed for trees growing in seasonally water‐stressed environments: drought tolerance and drought avoidance. These are respectively associated with evergreen phenology, where plants retain their leaves throughout the year, and deciduous phenology, where plants drop their leaves during dry seasons. Evergreen species are thought to have leaf traits supporting lower photosynthesis and transpiration rates, in order to conserve water during dry periods. We evaluated 18 morphological, chemical and physiological leaf traits of 51 abundant savanna tree species that differed in leaf habit (deciduous and evergreen), selected from two climate types (semi‐arid and humid) in three continents (Australia, Africa and South America) (annual rainfall range: 500–1550 mm), and grown in a common garden experiment. We hypothesised that evergreen species have more conservative water use and differ more across climate types than deciduous species because evergreen species are forced to endure extended water deficits during dry seasons. Trait shifts between semi‐arid and humid savannas did not differ between evergreen and deciduous species. Evergreen species had similar assimilation rates but lower photosynthetic water‐use efficiency (PWUE) than deciduous species, possibly to extend their leaf lifespans by protecting their photosynthetic machinery from overheating through evaporative cooling. Species of humid and semi‐arid environments did not differ with respect to assimilation rate or PWUE, but semi‐arid species did have smaller leaf sizes and greater leaf potassium and phosphorus concentrations. These traits may enable semi‐arid species to maximize growth during episodes of favourable moisture availability. Species from the three continents differed in their leaf traits. These probably reflect the greater proportion of evergreen species in Australia as compared to the other continents and generally infertile soils in the South American sampling sites compared to the wider fertility range in the African sites. Synthesis: Water stress in savannas does not select for more conservative water use, but may select for rapid adjustment to prevailing water conditions and for heat avoidance mechanisms.

Background and Aims Plant relative growth rate (RGR) depends on biomass allocation to leaves (leaf mass fraction, LMF), efficient construction of leaf surface area (specific leaf area, SLA) and biomass growth per unit leaf area (net assimilation rate, NAR). Functional groups of species may differ in any of these traits, potentially resulting in (1) differences in mean RGR of groups, and (2) differences in the traits driving RGR variation within each group. We tested these predictions by comparing deciduous and evergreen savanna trees. Methods RGR, changes to biomass allocation and leaf morphology, and root non-structural carbohydrate reserves were evaluated for juveniles of 51 savanna species (34 deciduous, 17 evergreen) grown in a common garden experiment. It was anticipated that drivers of RGR would differ between leaf habit groups because deciduous species have to allocate carbohydrates to storage in roots to be able to flush leaves again, which directly compromises their LMF, whereas evergreen species are not subject to this constraint. Key Results Evergreen species had greater LMF and RGR than deciduous species. Among deciduous species LMF explained 27 % of RGR variation (SLA 34 % and NAR 29 %), whereas among evergreen species LMF explained between 2 and 17 % of RGR variation (SLA 32–35 % and NAR 38–62 %). RGR and LMF were (negatively) related to carbohydrate storage only among deciduous species. Conclusions Trade-offs between investment in carbohydrate reserves and growth occurred only among deciduous species, leading to differences in relative contribution made by the underlying components of RGR between the leaf habit groups. The results suggest that differences in drivers of RGR occur among savanna species because these have different selected strategies for coping with fire disturbance in savannas. It is expected that variation in the drivers of RGR will be found in other functional types that respond differently to particular disturbances.

In this article, we review allelopathy studies conducted in Brazil or involving plant species that occur in the country. Conceptions and misconceptions associated with allelopathy, as well as some international criteria to be applied in allelopathic research, are presented and discussed. We observed a sharp increase in the number of papers on this subject conducted in Brazil between 1991 and 2010. However, most studies are conducted under laboratory conditions, lack a clear hypothesis or a solid justification, and typically make use of target species that do not co-exist with the donor species under natural conditions. We also found that most studies do not take the additional steps in order to purify and identify the bioactive molecules. We recommend that further studies be conducted in order to explore the potential of plant biodiversity in Brazil. Such studies could lead to the development of new molecular structures (allelochemicals) that could be used in the control of pests and weeds, thereby reducing the use of the harmful synthetic herbicides that are currently being widely employed

Question: In seasonal rainfall systems, seed dormancy is a strategy to avoid germination and seedling emergence in the dry season. Grass species in Brazilian savannas (Cerrado) show variation in seed dispersal timing and mechanisms, and occur in different habitat types (distinguished by soil moisture) within a seasonal rainfall environment. However, it is unknown whether dormancy has evolved in these systems as a dominant way in which germination is deferred, or how it correlates with other key traits such as dispersal, where known trade‐offs exist for avoiding competition. We asked whether seed germination and dormancy vary with dispersal and abiotic factors in savanna systems. Specifically, we assessed dormancy by comparing seeds: (1) from species living in habitats with contrasting soil moisture during the dry season (open savannas vs wet grasslands); (2) dispersed at different times (early in the wet season, late in the wet season and in the dry season); and (3) showing alternate dispersal syndromes (barochoric vs anemochoric).Location: Open savannas and wet grasslands in central Brazil.Methods: We collected seeds of 29 grass species and tested viability and dormancy using germination trials with fresh seeds, which was then repeated after dry storage for 3, 6, 9 and 12 mo. GLMM were used to test whether the degree of dormancy was dependent on habitat type, seed dispersal time and seed dispersal syndrome.Results: Seeds from wet grasslands lived longer and had consistently higher germination rates than seeds from open savannas. Additionally, fresh seeds dispersed late in the wet season had higher levels of seed dormancy compared to seeds dispersed early in the wet season. Finally, we found that anemochoric seeds had lower levels of dormancy than barochoric seeds.Conclusions: Seed dormancy among Neotropical grasses was higher for seeds of species from dry habitats, dispersed late in the wet season, and with short distance dispersal (barochory). These results suggest that seed dormancy is a key mechanism by which seeds avoid seedling emergence in the dry season, an effect offset by habitat‐specific soil moisture availability. The trade‐off between dormancy and seed dispersal suggests that both strategies are costly and had non‐additive benefits.