Banco de sementes do solo de três fitofisionomias da Floresta Nacional do Araripe, Ceará, Brasil

Abstract

Due to the current degradation of forests, researches have been performed to understand the natural regeneration process of these areas. Regeneration from seeds stored in the soil seed bank is an important strategy on the ecosystems dynamics. Soil seed bank can present different in time and space and vary in relation to the different phytophysiognomies or microhabitats in an area and vary in response to the influence of precipitation in environments with a high seasonality. Therefore, this study aims to detect the influence of variables like different phytophysiognomies, depths of seed deposition in the soil and climatic seasons on the species richness and seed density in the soil seed bank of three phytophysiognomies of Araripe National Forest, Ceará, Brazil. Soil seed bank samples was performed in cerrado sensu strictu, cerradão and semideciduous seasonal forest (humid forest) at the end of the rainy and dry seasons where, in each, it was collected 50 samples of litter and mineral soil (0-5 cm depth). To determine species richness and composition and seed bank density, it was performed the seedling emergence method. GLM was used to verify the influence of phytophysiognomies, depths and seasons on the richness and seed density. To detect differences in the mean values of richness and density it was performed a post-hoc Tukey test (5%). A NMDS was used to compare the seed bank structure between phytophysiognomies and the similarities was verified with ANOSIM test. SIMPER function was used to indicate the contribution percentage of each species for the dissimilarity between samples. It was registered 24, 29 e 30 species and 174, 261 and 399 seeds.m-2 in cerrado, cerradão and humid forest seed banks, respectively. In cerrado and humid forest, both species richness and seed density, is in the litter or in the soil, did not differ among climatic seasons. In cerradão, both species richness and seed density observed in the mineral soil were significantly different among seasons. Depth shows a higher explanatory power on the variation of species richness (50.63%) and seed density (22.73%), followed by phytophysiognomy (8.95% and 4.18%, respectively for the species richness and seed density). Only the variable climatic season in a given year did not allow to predict the seed density variation and their low influence power on the species richness leads to suggest that the occurrence of a seasonal pattern and its interaction with others variables is complex, making it difficult to understand the soil seed bank dynamic in forests.