Estratégias reprodutivas de plantas de sub-bosque de Floresta Atlântica em diferentes estádios sucessionais

• Ano de defesa: 2013
• Autor(a) principal: Fonseca, Rúbia Santos
• Orientador(a): Vieira, Milene Faria
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Botânica
• Departamento: Botânica estrutural; Ecologia e Sistemática
• País: BR
• Palavras-chave em Português: Orquídea - Reprodução; Polinização; Mata Atlântica
• Palavras-chave em Inglês: Orchid - Reproduction; Pollination; Atlantic Forest
• Área do conhecimento CNPq: CNPQ::CIENCIAS BIOLOGICAS::BOTANICA
• Link de acesso: http://locus.ufv.br/handle/123456789/374

The reproductive traits of a plant community are influenced by its disturbance history. Mata do Paraíso is an Atlantic Forest fragment with 195 ha in the municipality of Viçosa, Minas Gerais State, Southeastern Brazil. It comprises different environments that have undergone varied uses corresponding to the following successional stages: abandoned pasture (Pasture) and forests at early (FEI), intermediate (FEM) and advanced (FEA) stages of regeneration. To understand the distribution of reproductive strategies in this plant community, it is necessary to analyze the species in relation to their successional stages. The objectives of this study were: 1) to examine the distribution of frequency (% of species) and abundance (% of individuals) of the sexual system in the different growing habits and in the understory plant species at the four successional stages, 2) to verify whether the flower age of Corymborkis flava, a terrestrial orchid that grows in areas of advanced regeneration (FEA), affects pollination efficiency; 3) to confirm the autogamy in Cyclopogon variegatus Barb. Rodr., a terrestrial orchid that grows in areas of intermediate regeneration (FEM), as well as to describe the self-pollination mechanism and interpret the ecological consequences of this reproductive strategy. For the first objective, 24 plots were distributed in different successional stages for identification of plant species, their growing habits, the sexual systems and the abundance of individuals per plant species. For the second objective, flowers of C. flava were undergone to morphological evaluations (aspects of the perianth and stigmatic area), chemical test (test for enzymatic activity with hydrogen peroxide) and hand-pollination tests. For the third objective, flowers of C. variegatus were analyzed using light microscopy (anatomical sections) and fluorescence; besides, we made tests of pollination and the viability of seed, observations of pollinators and pollinaria removal. We find five sexual systems: hermaphroditism (in 80.5% of the species), dioecy (12.4%), monoecy (5.3%), andromonoecy (0.88%) and gynomonoecy (0.88%). The growing habits and the successional stages interfered in the distribution of sexual systems. We observed association of herbs with hermaphroditism, of vines with monoecy and treelets with dioecy. Andromonoecy and gynomonoecy were restricted to herbs. Regarding to stages, andromonoecy was restricted to Pasture, gynomonoecy to FEI; no monoecy was observed in FEA and dioecy prevailed at this stage. Such differences seem determined by the range of habits in each successional stage. The frequency or abundance of sexual systems related with growing habits allowed the same conclusion: habits distribution is related to distribution of sexual systems. However, to successional stages the frequency or abundance resulted in different conclusions. The abundances of sexual systems differed between stages, while the frequencies were similar. Morphological observations and chemical test, in C. flava flowers, were equally effective in defining the period of stigmatic receptivity as well as pollination. However, the greater fruit settting on the first and second day of anthesis showed that the best method to define the stigma receptivity, including its magnitude, was hand-pollination. We conclude that, for orchid species with long-lasting flowers, cross-pollination in vivo is recommended to evaluate the maximum degree of stigmatic receptivity and the real reproductive potential of the flowers. The functional morphology of the C. variegatus column is distinct of the column of the other Spiranthoideae species. These differences include the stigmatic area in the clinandrium cavity, unique feature, and the loss of herkogamy, promoting obligatory autogamy. This self-pollination mechanism is new to orchids and seems to have favored the establishment of the population in the study area, where pollinators are absent. All these results demonstrated that the understory plant species of Atlantic forest present a variety of reproductive strategies, which ensure their survival in environments with different levels of disturbance.