Respostas ecofisiológicas de plântulas de duas espécies arbóreas de diferentes estágios sucessionais da várzea, Amazônia Central

Abstract

The flood pulse, responsible for the high dynamic in the Amazon floodplains, submits the forests along the river banks to an annual, periodical and monomodal flood. Co-acting with the flooding, a light gradient takes place. To understand the establishment mechanisms of seedlings in floodplains, the ecophysiology adaptation of two distinct successional strategies species to flood and luminosity was investigated. In this study the selected species were Cecropia latiloba, a flood-tolerant pioneer and Pouteria glomerata a late secondary shadetolerant. Along the period of six months, monthly measures of gas exchange were made (photosynthetic assimilation, stomatal conductance, ratio of intercellular CO2 concentration to CO2 concentration in the curvette and water use efficiency) and the chlorophyll a fluorescence, as well as the height and number of leaves in 20 seedling taken from the Marchantaria island. One single leaf per seedling (fully expanded and light exposed) was selected and subjected to two light intensities and flood regimes (n = 5). After this period, the leaf area was measured and subsequently, the seedlings were divided in leaves, stem and root, to obtain the dry mass. The results reveal that the optimal development of C. latiloba is strongly related to high light availability, when the seedlings showed the highest values of gas exchange and growth, however, independently of the treatment, this species allocated biomassa in height (elongation stem) and the leaf turnover. On the other hand, the water use efficiency decreased under higher light, and increased in the absence of flood. For P. glomerata, the data shows that the specie is more affected by the flood, decreasing gasexchange and quantum efficiency rates. P. glomerata demonstrated a different growth strategy, decreasing the investment in height and maintaining its leaves. The results show that the pioneer species, very abundant in lower parts of floodplains, perform a more efficient strategy for its establishment, as high production of adventitious roots, in order to allow the maintenance of the metabolism during longer periods of flooding and the physiological and morphological responses in favor environments with high light. However, this late secondary showed strong relation of metabolic reduction with the flood, what may be a consequence of the anaerobic metabolism activation. During the aquatic phase, the sum of flooding and low light for seedlings characterizes a temporary unfavorable condition in floodplains. To tolerate this period, C. latiloba and P. glomerata show distinct eco-physiological responses that justify their establishment under the conditions imposed by the flood pulse.