Ecofisiologia de sementes de espécies nativas dos campos de altitude do Itatiaia (RJ): uma abordagem baseada nas previsões das mudanças climáticas provocadas pelo aquecimento global

Abstract

Tropical montane grasslands are found on mountain tops, associated to the Atlantic Forest and Amazon. Due to their isolation and edaphoclimatic characteristics, this ecosystem is an important center of diversity and endemism. There are no seed eco-physiological studies of this plant community, and considering the vulnerability and threatened by anthropogenic actions and climate change, it becomes relevant the knowledge about germinations strategies under different germinative approaches. In this work, 68 plant species from Itatiaia tropical montane grasslands were collected to evaluate the germination behavior, viability, longevity, presence/absence of seed dormancy, and germination under abiotic stress conditions. Thus, different experiments were performed: constant (20°C) and alternating (15-25, 20-30 and 25-35°C) temperatures; presence/absence of light; effect of heat shock (80°C, 100°C and 120°C); effect of water stress (0.0; -0.15; -0.3; -0.4; -0.6; -0.8; -1.0MPa) versus temperature (15°C, 20°C, 25°C, 30°C, and 35°C); different storage conditions (cold-wet (10°C, 85%RH), cold-dry (10°C, 10%RH), and freeze-dry (-20°C, 10%RH)), besides the relationship with functional traits (seed mass, imbibition tax, life form and dispersion period). Most species did not show alternating temperature requirement, but demonstrated light requirement to germinate. Seed dormancy was found in most species, and physiological dormancy was the most frequent. In general, seeds showed small size that was significantly correlated with light requirement. Phanerophyte was the most frequent life form, and raining season was the most frequent among dispersion periods. Most species were sensitive or tolerant at 80°C, and only five species were stimulated by heat shock treatments. The functional traits of species showed significant effects with heat shock and water stress versus temperature on germinative responses. Germination was significantly affected by increasing of water stress and temperature. Storage conditions affected the germinative responses, which were reduced with the increase of temperature and duration of storage. Dry storage at 10°C and -20°C was able to maintain seed viability for 2.5 years in comparison to wet storage. The dormancy levels were affected by storage conditions, varying between species. These results indicate that germination responses are species‐specific to the environmental conditions, being important in structuring the tropical montane grasslands community. In addition, these results indicate that climate change will likely affect the germination stages. Thus, the predicted warmer and dryer climate will affect the recruitment of many species, resulting in altered proportions of germination and subsequently change in community composition of this ecosystem. Additionally, similar to mountain ecosystems in the world, actions to mitigate the effects of climate changes on vegetation of topical montane grasslands, are urgent before many species becomes critically endangered. In addition, these actions will be important to characterize the impact of climate change patterns and quantify their effects on organisms