Riqueza, composição e expressão sexual da comunidade de briófitas epífitas em florestas inundadas na floresta nacional de Caxiuanã, Amazônia oriental

Abstract

The flooded forests of the Amazon, called várzea and igapó, stand out for their historical, cultural, economic and ecological importance. The flora of these environments is rich and diverse, however there are still gaps on its composition, for example, on its epiphytic bryoflora. Little is known about the richness, composition and sexual expression of bryophytes in these environments and on what are the effects of flooding and seasonality present in the region on these species. The aim of this study was to determine if there is variation in richness, in the composition and sexual expression of epiphytic bryophytes community in relation to climatic seasonality and the types of flooded forests in the Floresta Nacional de Caxiuanã. The sampling took place in two different periods, including periods of drought and rainy, six excursions held between July/2013 to June/2014. The collections of bryophytes were performed in plots of the Programa de Pesquisas Ecológicas de Longa Duração (PELD) and in adjacent areas to those, within the várzea and igapó forests. Phorophytes of Virola surinamensis (Rol. ex Rottb.) Warb. located in these areas were selected for sampling and only phorophytes with CBH> 20 cm were used. The botanical material was taken on the trunk of phorophytes in a standardized way, using the dimensions of 20 x 20 cm. Was established 1.30 m height from the ground for the collections. The absolute frequency of species was based on the occurrence of these on the selected phorophytes. In order to compare the richness of bryophytes by phorophytes in relation to forest types and periods of drought and rainy, was performed the two-way ANOVA with the normality determined by Shapiro–Wilk test. To test the differences in species composition between forest types and periods of lowest and highest precipitation was used an ordering multivariate analysis with Sørensen similarity index and as binding measure the nearest neighbor. During identification, the species were analyzed for the presence of fertility, reproduction types, sexual system and reproductive structures. The chi-square test was performed to compare the occurrence of fertile individuals of each species of bryophytes in different environmental conditions (drought or rain and igapó or várzea forest). 502 samples of bryophytes were analyzed, resulting in 54 species distributed in 13 families, being the Lejeuneaceae the richest with 30 species (55%). The igapó forest got the greater richness with 44 species compared to várzea forest, with 38 species. There was no significant difference in the number of species in relation to periods of drought and rainy. The ordering analysis showed two groups, demonstrating differences in the species composition of bryophytes community between the igapó and várzea forests, but not between periods of drought and rainy. Of the 54 identified species, 34 were fertile and only seven met the prerequisites to be analyzed for fertility using the chi-square test. There was no standard for sexual expression (fertility) of the seven analyzed species between the forests (várzea and igapó) and between periods (dry and rainy). The results demonstrate that both epiphytic bryophytes composition and sexual expression of some species is consistent with what is known for tropical forests, reinforcing the need for studies including reproductive strategies of bryophytes in different environmental conditions.