Dispersion phenology and germination strategies of woody and herbaceous plants in the Brazilian Savanna

Abstract

The initial stages of the life cycle of plants are the most vulnerable during their ontogeny, and are important determinants of the patterns of distribution, abundance, diversity and the dynamics of plant communities. Under seasonal climate the germination in the beginning of the rainy season maximizes the period favorable for seedling establishment, allowing the seedlings to withstand the conditions of low water availability during the upcoming dry season. Thus, germinate in the onset of the rainy season is of vital importance for the successful recruitment of plants in seasonal environments. Nevertheless, in seasonal environments seed dispersal occurs throughout the year and community level studies on the ecology and evolution of dormancy are virtually nonexistent in the Cerrado. In this sense, this proposal seeks to: (i) Describe the variation in the proportion of species with dormancy in the cerrado according to the life form, season and dispersal syndrome, (ii) estimate the germination time in the field, (iii) assess whether the type of dormancy is related to life form, phenology, dispersal mode, seed moisture content and fresh weight, (iv) determine how many times the dormancy and their types have evolved in the cerrado, and what are the processes that drive the evolution of dormancy in this vegetation, and (v) evaluate whether species that exhibit long periods of seed dispersion display intraspecific variation in the degree of seed dormancy, and whether this variation presents a temporal pattern. The study will be conducted in a cerrado ss and a campo sujo at Itirapina, SP, Southeastern Brazil. Woody species will be chosen based on seed production from a preliminary list of 52 species whose phenology has been monitored in the cerrado ss since 2004 by the Laboratory of Phenology at UNESP / RC; the choice of herbaceous plants will be carried out during fortnight trips to Campo Sujo. The germination tests will be peformed at 25° C under constant white light. Dormancy will be classified as physical, physiological, morphophysiological, morphological, or combinational. The degree of dormancy will be measured by mean base water potential (¨b(50)) as the model hydrothermal time. Our study will help to understand the mechanisms allowing the maintenance of diversity in tropical savannas. The study will broaden our comprehension of the effects of the severity of climate to define the strategies that control the germination time of species and life forms in tropical areas under seasonal climate. Finally, the information generated will be useful in conservation and ecological restoration programs, through the planning of seed collection, and treatments to break dormancy. (AU)