The aim of this review is to comment on the available data about germination of seeds from herb, shrub and tree species of the Cerrado after the publication of the review written by Felippe and Silva in 1984. Studies on seed germination of herbaceous species focused mainly on the responses of seeds to light, different ranges of temperature and storage in the soil. The majority of seeds from herb species germinate between 20°C and 30°C, and are photoblastic. Alternate temperatures favored germination in some seeds, but changed light sensitivity of the achenes of Bidens gardneri. Seeds of most of the shrub species of Melastomataceae are positive photoblastic; among the Velloziaceae, germination in the dark was observed in some species. Other shrub species show dormancy caused by impermeability of the seed tegument, as described for seeds of some species of Bauhinia. Their dormancy is broken by chemical scarification using sulphuric acid. Seeds of Heteropterys pteropetala are sensitive to very high temperatures, similar to those registered during burnings. Some species were considered to have allelopathic effects and could inhibit the germination of seeds of other species and the establishment of plantlets. Seeds of most tree species do not require light to germinate and the focus of the studies were on methods of dormancy breaking. Sulphuric acid and incisions in the tegument proved to be the most efficient methods to break dormancy. In general, the studies are limited to three major aspects: responses to light, effects of different temperatures and dormancy breaking. More studies are necessary to understand the physiological and biochemical aspects of reserve compounds and their mobilization during germination, as well as the effects of fire in these seeds. Key words: dormancy, photoblastism, soil seed bank, temperature Germinação de sementes de espécies de Cerrado: O objetivo desta revisão é comentar dados disponíveis sobre a germinação de sementes de espécies herbáceas, arbustivas e arbóreas do Cerrado, desde a publicação da revisão feita por Felippe e Silva na década de 1980. Estudos de germinação de sementes de espécies herbáceas do Cerrado enfatizam as respostas das sementes à luz, temperatura e armazenamento no solo. A maioria dessas sementes germina entre 20ºC e 30ºC e são fotoblásticas. Temperaturas alternadas nem sempre favoreceram a germinação das sementes, no entanto, alteraram a sensibilidade à luz em aquênios de Bidens gardneri. A maioria das sementes das espécies arbustivas de Melastomataceae estudadas apresentaram fotoblastismo positivo; entre as Velloziaceae, foi observada germinação no escuro em algumas espécies. Sementes de algumas espécies arbustivas possuem dormência causada pela impermeabilidade do tegumento, quebrada com imersão em ácido sulfúrico, como no gênero Bauhinia. Sementes de Heteropterys pteropetala são sensíveis a temperaturas altas, similares àquelas registradas durante as queimadas. Plantas de algumas espécies têm efeitos alelopáticos e podem inibir a germinação de sementes de o...
The germination of three cerrado herbaceous species: Bidens gardneri, Vernonia herbacea (Asteraceae) and Psychotria barbiflora (Rubiaceae) was studied using seeds stored in cerrado soil and in refrigerator at 4°C. The field experiment was carried out at a preserved area of cerrado, the Reserva Biológica e Estação Experimental de Mogi-Guaçu, State of São Paulo, Brazil. The soil was collected in the same cerrado where the experiment was carried out. The achenes of Bidens gardneri are light sensitive, but this sensitivity disappeared when the achenes were stored in soil. With 3 months storage in cerrado soil no differences in germination in light or darkness were detected. The number of intact achenes retrieved from storage in soil decreased with increasing time of storage. A large number of seeds had already germinated during the 3 months storage in soil. The longevity of seeds of this species stored for nearly 10 years at 4°C was checked: the achenes were viable for a long period of time but less than 10 years. Intact achenes of Vernonia herbacea could be retrieved from the soil only with 1 month storage. Germination was always very low and only 15% of the achenes possessed embryos. The number of intact seeds of Psychotria barbiflora decreased the longer the period of storage in soil. Germination of seeds stored at 4°C or in the soil was always very low. From the germination studies of stored seeds in cerrado it can be concluded that Vernonia herbacea does not form a seed bank and Bidens gardneri and Psychotria barbiflora may form a temporary seed bank in cerrado.
Carbon allocation in biomass is an important response of plants to the increasing atmospheric [CO2]. The effects of elevated [CO2] are scarcely reported in fructan-accumulating plants and even less in tropical wild species storing this type of carbohydrate. In the present study, the effects of high [CO2] atmosphere was evaluated on growth, biomass allocation and fructan metabolism in Vernonia herbacea (Vell.) Rusby, an Asteraceae from the Brazilian cerrado, which accumulates inulin-type fructans in the underground organs (rhizophores). Plants were cultivated for 120 days in open-top chambers (OTCs) under ambient (~380 μmol mol–1), and elevated (~760 μmol mol–1) [CO2]. Plant growth, photosynthesis, fructan contents, and the activities of fructan metabolising enzymes were analysed in the rhizophores at Time 0 and 15, 30, 60, 90 and 120 days. Plants under elevated [CO2] presented increases in height (40%), photosynthesis (63%) and biomass of aerial (32%) and underground (47%) organs when compared with control plants. Under elevated [CO2] plants also presented higher 1-SST, 1-FFT and invertase activities and lower 1-FEH activity. Although fructan concentration remained unchanged, fructan productivity was higher in plants maintained under elevated [CO2], due to their higher rhizophore biomass. This is the first report on the effects of elevated [CO2] on a plant species bearing underground organs that accumulate fructans. Our results indicate that plants of V. herbacea can benefit from elevated atmospheric [CO2] by increasing growth and carbon allocation for the production of inulin, and may contribute to predict a future scenario for the impact of this atmospheric condition on the herbaceous vegetation of the cerrado.
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