Fabian Borghetti

Requerimentos de luz e temperatura para a germinação de sementes de Aechmea nudicaulis (L.) Griesebach e Streptocalyx floribundus (Martius ex Schultes F.) Mez (Bromeliaceae)

Palavras-chave - Aechmea nudicaulis, Streptocalyx floribundus, restinga, germinacao, temperatura ABSTRACT - (Light and temperature requirements for germination of seeds of Aechmea nudicaulis (L.) Griesebach and Streptocalyx floribundus (Martius ex Schultes F.) Mez (Bromeliaceae)). Seeds of A. nudicaulis and S. floribundus were collected in a restinga located at Presidente Kennedy (ES, Brazil). This sandy community is characterized by the presence of patches of vegetation interspersed by open areas with a sparse plant covering. In order to evaluate the capacity of A. nudicaulis and S. floribundus to recruit individuals from seeds in the distinct microclimates generated by this heterogeneous plant covering, experiments were conducted in laboratory to test the effects of light and temperature on the germination for both species. Seeds of A. nudicaulis were unable to germinate in darkness but they achieved high germinability (≥90%) from 15 to 40°C under red light. Seeds of S. floribundus germinated in darkness only at 40oC (22.5%), whereas the germinability was high (≥90%) from 15 to 30oC under

Leaf adaptations of evergreen and deciduous trees of semi-arid and humid savannas on three continents

Summary 1. 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. 2. 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. 3. Trait shifts between semi-arid and humid savannas did not differ between evergreen and deciduous species. 4. 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. 5. 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. 6. 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. 7. 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.

Efeito alelopático de folhas de Solanum lycocarpum A. St.-Hil. (Solanaceae) na germinação e crescimento de Sesamum indicum L. (Pedaliaceae) sob diferentes temperaturas

Allelopathy should be defined as any stimulatory or inhibitory effect by one plant on another through production of chemical compounds released into the environment. Several Solanum species have shown some allelopathic property. S. lycocarpum islargely distributed on disturbed areas of the Brazilian Cerrado. In the present study the effects of aqueous extracts of S. lycocarpum leaves on the germination and growth of Sesanum indicum L. (sesame) were investigated. Aqueous leaf extracts at concentrations of 1%, 2%, 3%, 4%, and 5% (w/v) were prepared. The osmolarity of the extracts were measured and solutions of polyethylene glycol (PEG 6000) of similar osmolarity were prepared to evaluate osmotic effects of the extracts on sesame germination and growth. The experiments were carried out on petri dishes lined by two layers of filter paper plus the solutions to be tested. For the germination experiments the number of germinated seeds was checked every 8h. For the growth experiments sesame seeds were previously germinated in water and disposed to grow in the extracts. After five days of incubation the root and shoot length of the seedlings was measured. All the experiments were performed at 22 oC, 30 oC and 38 oC. The extracts did not affect the germinability but increased the average germination time in a dose-dependent manner at the three temperatures. The root growth was more affected by the extracts, showing tip-necrosis, absence of root hairs, and formation of secondary roots. These effects were more evident at 38 oC. Using PEG 6000 it was shown that the observed effects were not due to osmotic properties of the leaf extracts.

TEMPERATURE-DEPENDENT GERMINATION AND ENDO-β- MANNANASE ACTIVITY IN SESAME SEEDS†

O efeito da temperatura sobre a germinacao e a atividade de endo-b-mananase em sementes de Sesamum indicum foi investigada. A temperatura minima de germinacao (Tmin) esta localizada entre 12,8°C e 13,2°C enquanto a temperatura maxima (Tmax) encontra-se entre 45,5°C e 46°C. As germinabilidades (G%) nao foram significativamente diferentes da viabilidade estimada (88%) entre 18,8°C e 43,2°C. O teste de Mann-Whitney apontou o intervalo de 31,9°C a 35,1°C como sendo a faixa de temperatura otima (Tot). Quando sementes incubadas a temperaturas proximas ou abaixo de Tmin e proximas ou acima de Tmax foram transferidas para 30°C, aquelas submetidas a baixas temperaturas atingiram germinabilidade elevada. Por outro lado, quanto maior a temperatura de pre-incubacao acima de Tmax, menor a germinabilidade alcancada. O principal monossacarideo encontrado na parede celular do endosperma das sementes foi manose. Somente em temperatura supra-otima foi observada elevacao na atividade de endo-b-mananase na regiao micropilar do endosperma anterior a germinacao.

Relative growth rate variation of evergreen and deciduous savanna tree species is driven by different traits.

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.

Produção e germinação de sementes de "capim dourado", Syngonanthus nitens (Bong.) Ruhland (Eriocaulaceae): implicações para o manejo

A venda de artesanato feito com escapos de S. nitens e uma importante fonte de renda na regiao do Jalapao, TO. Conhecer a epoca de producao e dispersao das sementes, bem como seu potencial germinativo, e essencial para propor formas de manejo que garantam a sustentabilidade economica e ecologica deste extrativismo. Com o intuito de caracterizar a epoca de producao de sementes foram coletados capitulos entre agosto e dezembro/2003. Foram realizados experimentos de germinacao em câmara a 22-30 oC, sob foto e termoperiodo de 12 horas, e tambem em condicoes de escuro. Caracterizou-se tambem a germinacao em condicoes de hipoxia (imersao em agua) e acidez (pH 4 e 5). A producao de sementes iniciou-se em setembro e a maior parte da dispersao ocorreu entre outubro e novembro. A germinacao das sementes coletadas entre setembro e outubro foi de 92 ± 7% (media ± DP), sementes coletadas a partir de novembro tiveram germinacao significativamente menor. A acidez e a hipoxia nao afetaram negativamente a germinacao em relacao ao controle. As sementes sao fotoblasticas positivas e mantem a germinacao apos congelamento a -20 oC. A colheita de escapos apos a frutificacao (a partir do final de setembro) e a dispersao manual das sementes pelos proprios extrativistas no momento da colheita sao estrategias importantes para o manejo da especie e nao prejudicam a atividade artesanal que esta focada nos escapos e nao nas flores, como ocorre para outras sempre-vivas.

Seed tolerance to heating is better predicted by seed dormancy than by habitat type in Neotropical savanna grasses

Open savannas and wet grasslands are present under the same seasonal macro-climate in central Brazil. However, in open savannas, temperatures during fires are higher than in wet grasslands. Grasses dominate both ecosystems and exhibit large variation in seed dormancy. We hypothesise that seeds of grass species from open savannas are more tolerant to heating than those of wet grasslands. Also, assuming that dormant seeds remain longer in the soil than non-dormant seeds – thus being more likely to burn – we expect that dormant seeds are more tolerant to heating than non-dormant seeds. We tested the effects of heating at 80 and 110°C for 2.5 and 5.0 min on the survival of seeds of 14 species, seven from each community, containing dormant and non-dormant species. Seeds of most species survived at 80°C, but seeds from open savannas maintained greater survival for 5 min than seeds from wet grasslands. Seeds of most species died at 110°C, but dormant seeds survived more than non-dormant seeds. We conclude that species with seed dormancy experience selection for covarying characteristics that allow tolerance to heating in hotter fires. Our findings suggest that both seed dormancy and habitat-specific fire temperatures may contribute to the evolution of seed fire tolerance in Neotropical savannas.

Avoiding the dry season: Dispersal time and syndrome mediate seed dormancy in grasses in Neotropical savanna and wet grasslands

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 versus 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 versus 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 of fresh seeds, which was then repeated after dry storage of 3, 6, 9 and 12 months. Generalized Linear Mixed Models 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 seedlings 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. This article is protected by copyright. All rights reserved.

Germination, initial growth, and biomass allocation in three native Cerrado species

The parameters of germination, initial growth, and biomass allocation of three native plant species of Cerrado (Copaifera langsdorffii, Dipteryx alata and Kielmeyera coriacea) were established. The species had germination percentages above 88% and average germination times longer than 139 hours. The average time for the opening of the first leaf pair was more than 538 hours for all three species. The average root length of C. langsdorffii and D. alata seedlings after 80 days of growth was around 40cm, four times larger than the average shoot length ( 20cm) of K. coriacea seedlings was four times larger than the average shoot length (<5cm), and the root biomass was 243% greater than the shoot biomass. Increase in seedling biomass was sustained primarily by the cotyledons in C. langsdorffii and D. alata, which acted as reserve organs and showed progressive weight reductions. Increase in seedling biomass in K. coriacea was sustained primarily by photosynthesis, since the cotyledons showed no significant weight reduction, acting primarily as photosynthetic organs. The length of the root systems was at least four times larger than the length of the shoots parts in all three species. Higher investment in root length rather than in root biomass suggest that the initial growth of these species is primarily to ensure access to water resources, apparently putting off the function of the radicular system as storage organ.

A simple procedure for the purification of active fractions in aqueous extracts of plants with allelopathic properties

Most studies conducted to test the allelopathic activity of plant parts have made use of water as solvent. However, the presence of polar, water-soluble substances, such as proteins and carbohydrates, tends to hamper the purification of active compounds. In this study, we present a simple purification procedure that separates the active fraction of the extract from the undesirable substances, thus facilitating the search for active molecules through standard chromatographic methods. Aqueous leaf extracts of three Cerrado species (Caryocar brasiliense, Qualea parviflora and Eugenia dysenterica) were prepared at 5% concentration (w/v) and stored at 4oC (crude extracts). After 24 h, these solutions were filtered and freeze-dried. The powder obtained was dissolved in methanol, filtered again, evaporated and dissolved in water for bioassays (purified extracts). For the bioassays, seedlings of Sesamum indicum were grown for five days in aqueous solutions prepared from crude and purified extracts at concentrations ranging from 0.1% to 1.0% (w/v). Seedling growth in distilled water was set as a control. In comparison with the control, we found that test solutions prepared from both crude and purified extracts significantly inhibited sesame seedling growth. However, solutions prepared from purified extracts were two to ten times more inhibitory to seedling growth than were those prepared from crude extracts. The inhibition of root growth ranged from 35% to 77%, depending on the plant species, at a concentration as low as 0.1%. Roots were more affected than were shoots. The effects of purified extracts on seedling morphology were similar to those observed when crude extracts were employed, indicating that the procedure of purification of crude extracts did not interfere with the mode of action of the active substances