RESUMO As sementes de palmeiras geralmente apresentam dormência e um endocarpo espesso que retarda a germinação e o crescimento do embrião, contudo, tratamentos com água podem acelerar o processo de germinação das suas sementes. Além disso, a conservação ex-situ de sementes pode causar perda de viabilidade das sementes de Arecacea especies ao longo do tempo. Dados sobre dormência e armazenamento de sementes têm sido negligenciados para muitas espécies de palmeiras nativas no Brasil. Por conta disso, nós investigamos o efeito da imersão em água e armazenamento de um ano sobre a germinação de sementes de Copernicia alba Morong, uma palmeira do Pantanal brasileiro. Pirênios recém-colhidos e armazenados foram imersos em água a temperatura ambiente por 24, 48 e 72h e água quente (~75°C por 5 e 10 min). Pirênios recém coletados germinaram 84% no controle, atingindo 100% após imersão em água por 48 e 72h. O armazenamento de um ano reduziu a germinação em ~50%, todavia, a imersão em água promoveu a germinação dos pirênios armazenadas. A água quente diminuiu a germinação dos pirênios frescos e os armazenados. De acordo com os resultados, sementes de C. alba podem ser classificadas em ortodoxas. Em geral, a imersão em água à temperatura ambiente aumentou a germinação dos pirênios. Entretanto, armazenamento for longa duração e tratamentos com água quente podem prejudicar a germinação.

ABSTRACT Palm seeds are known for displaying dormancy and a thick endocarp that delays germination and embryo growth, but water treatments may accelerate their germination process. Additionally, ex-situ conservation of arecaceae species may cause loss of seed viability over time. Data on seed dormancy and storage have been neglected for many native palm species in Brazil. Therefore, we investigated the effect of water treatments and one-year storage on the germination of Copernicia alba Morong, a palm tree from the Brazilian Pantanal wetland. Fresh and stored pyrenes were immersed in water (at room temperature for 24, 48, and 72h) and in hot water (~75°C for 5 and 10-min). Fresh pyrenes germinated up to 84% in control, reaching 100% after water immersion for 48 and 72h. One-year storage reduced germination by almost 50%, but water immersion slightly increased the germination of stored pyrenes. Hot water decreased germination for both fresh and stored pyrenes. Seeds of C. alba may be classified as orthodox seed storage behavior. Taken all together, water treatments at room temperature improved the germination of the pyrenes. In contrast, long-term seed storage and hot-water treatments may jeopardize germination.

ABSTRACT Fire-related cues may enhance seed recruitment in flammable ecosystems and differences in fire-germination responses of invasive vs. native species can drive the invasion process. We evaluated the effects of heat shock and smoke water solution treatment on seed germination of invasive (Melinis minutiflora, Urochloa decumbens, U. brizantha) and native grasses (Axonopus pressus, Aristida setifolia, Gymnopogon foliosus) of the Cerrado. The effect of fire temperature was tested by exposing seeds to heat shock treatments of 60, 100, and 200 °C for one minute, comparing them to untreated seeds. The effect of smoke was tested by soaking seeds for 24-h in an aqueous smoke comparing them to seeds soaked in distilled water. Differences among treatments were evaluated by ANOVA and randomization tests. None of the tested species had germination stimulated by the temperature or smoke. Both species of Urochloa experienced decreased viability with increasing temperature, while seeds of native species and M. minutiflora tolerated heat shock up to 200 °C. The invasive grasses usually germinated faster than the native grasses. Germination time is therefore a crucial trait driving the invasion process, irrespective of fire-related cues. Other seed traits (e.g. dormancy) and higher resprouting capacity may help invasive species to persist in frequently burned savannas.

Resumo: Modelos do tempo hídrico (θH) explicam a tolerância das sementes a potenciais hídricos reduzidos. Neste estudo, foi avaliada a capacidade dos modelos gráfico e probit para descrever parâmetros germinativos e tempos de germinação em uma leguminosa tropical (Peltophorum dubium). Foram conduzidos testes de germinação sob potenciais hídricos reduzidos (0 a -1.2 MPa) a 25 °C e utilizadas regressões para investigar a relação entre a taxa de germinação (1/t) e potencial hídrico para diferentes frações (10, 30, 50 e 70% de germinação). As regressões foram utilizadas no modelo gráfico para calcular θH (1/inclinação da reta entre taxa de germinação e potencial hídrico) e determinar os valores de potencial hídrico base (Ψb), ponto no qual a reta intercepta o eixo x (G% = 0). No modelo de probit, as porcentagens de germinação foram transformadas em probit e plotadas contra os valores de Ψb para descrever a germinação em uma única reta. Os valores de θH variaram de 1.8 a 2.0 MPa dia em ambos os modelos, e Ψb apresentou distribuição normal, conforme pressuposto pelo modelo probit. A maioria dos tempos de germinação (t10 e t50) preditos ficou dentro dos tempos observados, demonstrando relevância biológica dos modelos na descrição dos efeitos do potencial hídrico na germinação.

Abstract: Hydrotime (θH) models provide information on seed tolerance to low water potential and time to germination under different conditions. Here it was evaluated the capacity of graphic and probit model to describe germination parameters and germination times (t) in a tropical legume (Peltophorum dubium). Germination tests were conducted under reduced water potentials (polyethylene glycol solutions from 0 to -1.2 MPa) at 25 °C. Regression lines were applied to investigate the relationship between germination rates (1/t) and water potential for different germination percentages (fractions 10, 30, 50 and 70%). Those regressions were used in the graphic model to calculate θH (1/slope) and determine the base water potential (Ψb) as the point which the line intercepts the x-axis (G% = 0). In the probit model, germination percentages were transformed to probit units and plotted against Ψb-values to describe germination response under a single regression line. Values for θH varied from 1.8 to 2.0 MPa day in both models, and Ψb showed a normal distribution, as presupposed by the probit model. Predicted germination times (t10 and t50) mostly fell within observed times, thus showing biological relevance of the models to describe the effects of water potential on seed germination.

Fire plays an important role in several grassland ecosystems in the world. Fire can trigger germination in several species, by breaking the physical dormancy of their seeds. Thus, we hypothesized that exposure to high temperatures during fire would break seed dormancy and enhance germination. We tested the effect of high temperatures on the germination of six species of legumes from Brazilian subtropical grasslands. We used heat shock experiments with the following treatments: 60, 90, 120 and 150ºC for one minute. Seeds were then placed to germinate for 60 days in 12/12 hours light/dark and 20/30ºC. Germination was generally low for all study species. Most species was not affected by heat shock treatments. However, Stylosanthes montevidensis was the only species that had its physical dormancy broken when exposed to 120ºC. The seeds of all the other species were neither stimulated nor killed by high temperatures. Although the exposure to high temperatures did not affect the germination of the study species (except for one), it also did not kill seeds, thereby showing that seeds are resistant to fire. Therefore, the rapid passage of fire in these grasslands is not sufficient to break the dormancy of most of the studied species of legumes.