Fenologia, visitantes florais e sucesso reprodutivo de Struthanthus polyanthus Mart. (Loranthaceae) em três diferentes hospedeiros em uma área de cerrado

Abstract

Among a range of ecological interactions between different organisms, there is the parasitism. Some angiosperms, throughout their evolution, became parasites of other plants, called hosts. Hemiparasitic plants penetrate the host tissues through haustories, special structures that extract water and nutrients from xylem for their survival. Some studies have shown that the performance of parasitic plant can vary among host species, i.e., depending on the host in which the parasite is installed, it may have a higher or lower leaf, flower and fruit production, for example. Thus, the present study sought to investigate a dioecious and hemiparasitic plant, Struthanthus polyanthus Mart. (Loranthaceae), regarding the phenology, floral visitors and reproductive success, in three different hosts in a cerrado area of the Reserva Ecológica do Clube Caça e Pesca Itororó de Uberlândia, in Uberlândia city, Minas Gerais state, Brazil. The area has a cerrado sensu stricto phytophysiognomy and many species of the following host species: Cabralea canjerana polytricha (Meliaceae), Pouteria ramiflora (Sapotaceae) and Plathymenia reticulata (Fabaceae). The main hypotheses were: a) host species can influence the flowering intensity, but not the time of phenological events; and b) there is variation of floral visitors, fruit set and foliar nutritional quality of S. polyanthus among the different hosts. The results demonstrated in Chapter 1 show that the host species may influence the reproductive phenology, but not the vegetative phenology. Although there is a synchrony in the flowering period for male and female individuals of S.polyanthus, in all hosts, the production of buds, flowers and fruits is mainly influenced by the host species. Furthermore, the beginning and ending of phenological events of S. polyanthus did not vary according to the host, which reinforces the idea that the phenology of Cerrado species follows a pattern defined more intensely by abiotic factors, with great influence of seasonality. In Chapter 2, it was observed that there was a difference among the amount of foliar nutrients, the amount of pollen grains and in the richness and abundance of floral visitors of S. polyanthus in each host, with influence in the fruit set. The highest values were found on P. ramiflora. The most frequent visitors and with greater interaction strength were Apis mellifera, Trigona spinipes and Augochloropsis sp.1, being these considered effective pollinators. This study is the first to analyze the reproductive and vegetative phenology of S. polyanthus, as well as the floral visitors and the reproductive success of this hemiparasitic species, conditioned by the host species. It can be concluded, therefore, that different factors, whether abiotic or biotic, influence directly and indirectly the performance of S. polyanthus and that studies like this, analyzing tritophic systems, must be made for a better understanding of the processes that structure and shape the ecosystem.