ABSTRACT
Abstract We analyzed floristic variations in fern's metacommunity at the local scale and their relationship with abiotic factors in an Atlantic Forest remnant of northeastern Brazil. Floristic and environmental variations were accessed on ten plots of 10 × 20 m. We performed cluster analyses, based on Bray-Curtis dissimilarity index to establish the floristic relationship. The influence of abiotic factors: luminosity, temperature, relative air humidity and relative soil moisture was evaluated from a redundancy analysis. We found 24 species belonging to 20 genera and 12 families. The fern's flora showed high floristic heterogeneity (>75% for most of the plot's associations). The fern's metacommunity was structured along an abiotic gradient modulated by temperature, luminosity, and relative soil moisture.
Resumo Analisamos as variações florísticas na metacomunidade de samambaias em escala local e sua relação com fatores abióticos em um remanescente de Floresta Atlântica no Nordeste do Brasil. Variações florísticas e ambientais foram acessadas a partir de dez parcelas de 10 × 20 m. Realizamos análises de cluster, baseado no índice de similaridade de Bray-Curtis para estabelecer relações florísticas. A influência de fatores abióticos: luminosidade, temperatura, umidade relativa do ar e umidade relativa do solo foram avaliadas a partir da análise de redundância. Encontramos 24 espécies pertencentes a 20 gêneros e 12 famílias. A flora de samambaias exibiu uma elevada heterogeneidade florística (>75% para a maioria das associações entre plots). Observou-se que a metacomunidade de samambaias estava estruturada ao longo de um gradiente abiótico modulado pela temperatura, luminosidade e umidade relativa do solo.
Subject(s)
Ferns/classification , Biodiversity , Environment , Brazil , Adaptation, Physiological/physiology , Cluster Analysis , ForestsABSTRACT
The objective of the present study was to evaluate the electrophysiological effects of the peptide somatostatin (SST) at the supraventricular level in isolated guinea hearts. ECG recording from isolated hearts perfused by the Langendorff method i9ndicating that 1.0 uM SST induced a decrease in heart rate from 174 ñ 15 to 157 ñ 9 bpm (N=6, P<0.05), blocked AV conductio9n (the PR interval increased from 92 ñ 11 ms to 106 ñ 5 ms, N+5, P<0.05) and increased the QTc interval from 210 ñ 0 to 232 ñ 4 ms (N+5, P<0.05). The supraventricular effect of SST, particulary upon the AV conduction , were potentiated by a reduction in calcium concentration from 2.5 to 0.5 mM in the perfusing solution. Thus, 1.0 uM SST induced 2nd degree AV conduction block progressing to AV dissociation in 75% of thye hearts in the low calcium medium instead of the first degree conduction block observed in all hearts in normal calcium medium. His bundle electrogram evidence a complete A-H dissociation withouth significant change in the H-V interval and microelectrode studies showed a complete abolition of the AV node action potential in the presence of 1.0 uM SST. Both results demonstrate that the site of AV conduction block induced by SST is at the AV node. All the supraventricular effects of SST were transitory, subsiding within abouth 10 min of hormone exposition, showing desensitization. The effects of somatostatin here described were not blocked by 10 uM atropine, indicating that they are not mediated by muscarinic receptors. These data provide a direct electrophysiological demonstration of the supraventricular effects of SST, and suggest that this peptide decreases calcium influx during the action potential