A influência de variáveis ambientais sobre o crescimento foliar e um indicador de estresse fisiológico em quatro espécies herbáceas de subbosque na Amazônia central

Abstract

Although the patterns of herb distribution have been widely studied in recent years, little is known about their causes. In order to understand how distribution patterns may be linked to plant performance, growth, leaf dynamics and physiological stress of 4 species were monitored during 2 years. The study was conducted in an area of 4 km2 of terra- firme tropical Forest at Reserva Ducke, Manaus, Brazil. Individuals of each species (Monotagma spicatum- 29, Calathea altissima-36, Triplophyllum dicksonioides-43 and Spathanthus unilateralis-28) were selected over the entire amplitude of their distributions, and all leaves were tagged with plastic rings. Plants were visited at the end of the growing season of each year to count and measure new leaves, and note dead leaves. Physiological stress indicator (ratio Fv/Fm) was measured with a fluorimeter. Measures of soil texture, slope and light availability were obtained for each plant. The relationships between relative growth, leaf dynamics and physiological stress with the environmental factors were analyzed with multiple regressions. Most plants had null or negative balance between leaf gain and loss, and relative growth was negative or null in a least one of the years. Generally, growth was not better in the environmental conditions were the species are more abundant and physiological stress was not higher were they are not abundant. For some species, leaf dynamics was associated with terrain slope. Growth or leaf dynamics increased with light availability for the two species with more restricted distribution along the soil gradient, but not for the two soil generalist species, which seem to need a greater amount of light than included in the sample. Results indicate that understory herbs have slow growth, and suggest that distribution patterns are not determined by plant performance in response to environmental gradients after plants pass the initial establishment phase.