Características foliares, fluorescência da clorofila e alocação de biomassa em Ceiba pentandra em resposta ao sombreamento

Abstract

Ceiba pentandra (L.) Gaertn. (Malvaceae) – known as sumaúma – is a species of pantropical tree that displays a large size and fast growth, reaching up to 60 meters in height. It has a deciduous habit, losing all its leaves in the dry season. In Brazil, C. pentandra is naturally distributed throughout the Amazon River basin, occupying mainly the floodplains of flooded areas, but also found in terra firme areas. Thus, this study aimed at evaluating the leaf characteristics, chlorophyll fluorescence and biomass allocation in C. pentandra (L.) Gaertn. in response to the three levels of shading. The experiment was conducted next to the greenhouse of the National Institute for Research in Amazonia (INPA), Manaus-AM. Four different PAR conditions were used (TCtrl-1500 at full-sun, T1-800, T2- 200 and T3- 25 µmol m–2 s–1), which were obtained through the construction of PVC pipe tents covered with different layers of shade cloth. The experiment was started with seedlings of approximately one-year-old and lasted for 580 days. The parameters of photoinhibition, leaf chlorophyll content, biomass gain, water potential, stomatal density and soluble carbohydrate content were assessed for each treatment. Leaf lifespan was directly proportional to the level of irradiance, being higher in TCtrl (332,1±199 days), which was followed by T1 (318,3±109 days), T2 (200,5±154 days) and T3 (149,5±127 days), with a lower value. No signs of photoinhibition were observed for TCtrl (Fv/F= 0,76±0,04), T1 (Fv/Fm= 0,76±0,03) and T2 (Fv/Fm= 0,76±0,03). T3, however, showed low Fv/Fm means, remaining below 0,75 throughout the entire experimental period (Fv/Fm= 0,69±0,09). The lower levels of irradiance had less biomass accumulation, less stomatal density, less leaf water potential, smaller leaf area and lower total soluble carbohydrate. It was concluded that C. pentandra seedlings showed weak tolerance to shading, with a drastically low growth under low irradiance. Leaf lifespan was directly proportional to the level of irradiance, increasing with the increase in the level of PAR. The presence of photoinhibition in the seedlings of the maximum shading and its absence under high PAR concentrations demonstrates the species aptitude for growth in open areas.