RESUMO
To mitigate anthropogenic impacts on plant diversity in tropical montane grasslands, one of the most threatened ecosystems in Brazil, it will be essential to develop ex situ conservation strategies to preserve wild species. The lack of basic research on the seed storage behaviour of grassland species may, however, limit their use for reintroduction and restoration projects. We investigated seed storage behaviour at the community level by comparing the effects of cold-low RH (10 °C; 10% RH) and freezing-low RH (20 °C; 10% RH) conditions on seed viability, germination and dormancy of 47 species. Fresh seeds of 43% of the species showed primary dormancy. More than half of the species showed high seed survival responses (viability >60%) under both storage temperatures. Despite a variety of dormancy responses among the different species, the low RH storage conditions tested released dormancy for most species during 12- and 30-month storage times. Multivariate analysis of the best (freezing-low RH, 30 months) storage condition evidenced the formation of five distinct groups, three with species having high conservation potential in seed banks. Although further studies are needed to test dormancy-breaking treatments and improve seed conservation practices, this first approach to assessing seed banking techniques could contribute to demand for locally adapted seeds for ecological restoration projects in tropical montane grasslands.
Assuntos
Germinação , Dormência de Plantas , Brasil , Ecossistema , Pradaria , Sementes , TemperaturaRESUMO
Even though exhaustively studied, dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga remains a mystery. To clarify this, we asked the following question: could dormancy alleviation in diaspores of this species be associated with ageing, GA/ABA balance and remaining structures of the panicoid spikelet? We answer this question using diaspores of U. humidicola cv. BRS Tupi as a biological model, a cultivar with a wide edaphoclimatic range in Neotropical areas and whose diaspores possess 'deep dormancy' when dispersed. We analysed both germination and early plant development using a split-plot model. Our findings demonstrate that dormancy alleviation in diaspores of U. humidicola is a synergic phenomenon driven by crosstalk between age, GA/ABA balance and remaining structures of the panicoid spikelet covering caryopses, since this interaction acts on the dynamics of germination and early plant development. We demonstrate that: (i) spreading germination time is a maternal survival mechanism of this species, which has repercussions for occupational aggressiveness of the species; (ii) remaining structures of the panicoid spikelet covering caryopses are the main modulator of embryo development. These structures control the after-ripening process, which is modulated by some molecular factor. We also highlight that it is necessary to review concepts about dormancy of dispersal units in this grass species.
Assuntos
Dormência de Plantas/fisiologia , Poaceae/fisiologia , Dispersão de Sementes , Ecologia , Germinação/fisiologia , Poaceae/anatomia & histologia , Sementes/anatomia & histologia , Sementes/fisiologia , Clima Tropical , Água/metabolismoRESUMO
Miconia chartacea es un árbol con amplia distribución altitudinal y latitudinal en Brasil, que se encuentra desde formaciones vegetales estacionales xerofíticas como Caatinga y Cerrado hasta bosques pluviales como Mata Atlántica, en pastizales con árboles aislados hasta interior de bosques maduros. Fue descrita la respuesta germinativa de las semillas de M. chartacea a la luz, temperatura, hormonas vegetales y posmaduración a baja temperatura. Los frutos se recolectaron en la reserva de Cerrado "Prof. Karl Arens", en el municipio Corumbataí (San Paulo, Brasil), la cual presenta una estación seca y fría desde abril hasta septiembre y una estación húmeda y caliente de octubre a marzo. Las semillas se dispersaron durante la estación seca, son fotoblásticas positivas bajo temperaturas constantes y variables, la germinación disminuye bajo irradiaciones de luz blanca inferiores a 17 umol/m2s, la razón rojo/rojo lejano (R/RL) no afectó el porcentaje de germinación, pero la velocidad de germinación aumentó a partir de razones R/ RL > 0.4. Las semillas germinaron en el intervalo térmico de 15 a 35 °C, la temperatura optima esta entre 20 y 25 °C, la alternancia de temperatura no estimuló la germinación respecto a las temperaturas constantes. Las semillas presentaron latencia fisiológica no profunda, la cual fue rota mediante posmaduración durante 93 días a 7 °C y el etileno estimuló la germinación. La gama de temperaturas en la cual germinan las semillas fue menor en las semillas maduradas bajo las condiciones más calientes de la transición de la estación lluviosa a seca que las semillas maduradas en la estación seca. El requerimiento de un periodo frío para romper latencia disminuye la probabilidad de que las semillas germinen durante el invierno, quedando listas para germinar en el verano. Así, la detección de cambios estacionales de temperatura del suelo y el aumento de sensibilidad a la temperatura después de un periodo de frío son responsables por el control temporal de la germinación de M. chartacea, mientras que la respuestas a luz permite que solo germinen las semillas que están en la superficie del suelo, y favorece la germinación en claros de bosque pequeños a grandes.
Miconia chartacea is a widely distributed tree along both altitudinal and latitudinal gradients in Brazil, and it can be found in seasonal xerophytic vegetation, e.g. Caatinga and Cerrado, and tropical rainforest (e.g. Mata Atlantica), from grassland with scattered trees to mature forest. We studied the germination response of M. chartacea seeds to light, temperature, plant hormones and after-ripening at low temperature. Seeds were collected from a Cerrado reserve located in Corumbataí, Sao Paulo State, which characterizes to have a cool dry season from April to September, and a warm wet season from October to March. M. chartacea seeds are dispersed in the dry season and exhibited a photoblastic behavior both at constant and alternating temperatures. The germination was decreased at irradiances below 17 umol / m2s, whereas R: FR ratios below 0.4 reduced the germination rate, but not the germination capacity. The germination-permissive temperatures range from 15 to 35 °C, with an optimum interval from 20 to 25 °C. Germination is not improved by alternating temperature regimes as compared to isothermal treatments. The seeds have a non-deep physiological dormancy, which can be partially overcame either by dry after-ripening at 7 °C for 93 days, or by the 2-chloroethylphosphonic acid treatment. The thermal window within which the seeds germinate was narrower for seeds matured in the rainy to dry season transition period, under warmer conditions, than in the dry season. Cold requirement for dormancy break in seeds of M. chartacea can prevent the germination in the winter, allowing the seeds to germinate in the summer under more favorable conditions. The results suggest that seed response to temperature accounts for temporal distribution of germination, of M. chartacea, while light predominantly influences the spatial distribution of seedlings, precluding the germination of buried seeds and affecting the germination response to gap size.