Fenologia de Piper gaudichaudianum Kunth e P. vicosanum Yunck. (Piperaceae) em fragmento de Floresta Atlântica, com enfoque na biologia floral de P. vicosanum

• Autor(a) principal: Silva, Adriano Valentin da
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2561
• topic: Fenologia vegetal; Plantas - Reprodução; Pólen - Dispersão; Plant phenology; Plants - Reproduction; Pollen - Dispersion; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA

Phenological studies in Piper species are scarce. These plants are an important component in tropical forests understory and have similar floral and fruit attributes between species of the genus. Due to these similarities, including the habitat, phenological informations are particularly relevant because they aid to understand the maintenance of taxonomic identity and the aspects of the reproductive mechanisms in each co-occurring species. The flowers of Piper exhibit an asynchronous sequence in development of four (2, 1, 1) or six (2, 1, 1, 2) stamens. Studies have shown that dichogamy is common in flowers this genus. However, there is not information about the longevity of stigmas and the mode of exposure of their receptive areas associated with the release of pollen grains. Our goals were to analyze and compare vegetative and reproductive phenophases of two co-occurring Piper species, P. gaudichaudianum and P. vicosanum, and the influence of abiotic factors in their phenological behavior. Also, describe the chronology of pollen release of four stamens of P. vicosanum flowers, associating it with period of stigma receptivity and exposure mode of their receptive areas. The study was carried out from September/2008 to August/2010 in a fragment of Atlantic Forest located in the municipality of Viçosa, Minas Gerais State, southeastern Brazil. Twenty individuals of P. gaudichaudianum and 24 of P. vicosanum were monitored in the following phenological events: emission of sprouts (aerial stem formed from rhizome), leaf flush, production of spikes, abortion of spikes, flowering (flowers in pre-anthesis and anthesis), fruiting, and dispersal of spikes with fruits. Data were collected weekly and analyzed by activity index and, or by intensity. Additionally, was verified seasonality of the phenophases and their correlation with environmental variables. In the study of floral biology were evaluated receptivity of stigmas, with Peroxtesmo KO®, and viability of pollen grains, with acetic carmine. Field observations of periods of stigmatic receptivity and pollen release were made during 46 hours. Spikes were bagged to check the occurrence of spontaneous self-pollination. Aspects of floral biology were also analyzed with the aid of studies in light microscopy and scanning electron microscopy. For that, we applied the usual methods. With few exceptions, the phenophases were seasonal and positively correlated with environmental variables: mean temperature, precipitation, and, mainly, day length. Most of sprouts emitted by P. gaudichaudianum remained latent. In P. vicosanum, the sprouts produced spikes and they flowered, increasing the total number of spikes. The leaf flush, of the both species, occurred throughout or nearly throughout the year, with synchronous peaks in rainy season (October and November). The spikes produced by P. vicosanum, throughout the year, remained latent for up to 12 months. In P. gaudichaudianum the spikes were produced in the rainy season, between October and December, and flowered shortly thereafter. In both species, the abortion of spikes was higher than 73%. The species showed peaks of flowering (anthesis), fruiting and dispersion of spikes with fruits also in rainy season (October to March), without overlap of these events between them. Piper vicosanum presents incomplete protogyny (pistillate phase lasted until the sixth day) and were observed 100% of fruit set, probably due to the bisexual phase of the flowers; so it is self-compatible. The receptivity of stigmas lasted until 14 days and the exposure and senescence of stigmatic papillae occurred in staggered way, in basipetal direction, new characteristics to the genus. In senescent papillae there was accumulation of phenolic compounds in the same direction. The pollen release was asynchronously, following the sequence 1, 1, 1, 1, differs from the sequence of stamens development and is here described for the first time. The process of releasing pollen lasted up to six days. In conclusion, the species have distinct reproductive strategies, with temporal isolation of the reproductive phenophases, which are regulated by similar environmental variables. The set of the functional morphology of P. vicosanum - protogynous flowers, long periods of stigma receptivity and pollen release, and a bisexual phase of the flowers - seems to be key events for its reproductive strategies in the study area.