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

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.O pulso de inundação, responsável pela alta dinâmica existente nas áreas alagáveis da Amazônia, submete as florestas da margem dos rios a uma inundação anual, periódica e monomodal. Co-atuando com a inundação, um gradiente de luminosidade é observado. De forma a entender os mecanismos para o estabelecimento das plantas em áreas alagáveis, foram investigadas as adaptações ecofisiológicas de duas espécies de diferentes estágios sucessionais à inundação e luminosidade. Neste estudo as espécies selecionadas foram Cecropia latiloba, uma pioneira tolerante a inundação e Pouteria glomerata, uma secundária tardia tolerante a sombra. Ao longo de seis meses foram feitas medidas mensais de trocas gasosas (assimilação fotossintética, condutância estomática, razão da concentração de CO2 intracelular / concentração de CO2 do ambiente, eficiência no uso da água) e fluorescência da clorofila a, bem como de altura e número de folhas em 20 plântulas retiradas da Ilha da Marchantaria. Utilizou-se uma folha por plântula (totalmente expandida e exposta à luz solar), as quais foram submetidas a duas intensidades de luz e inundação (n = 5) durante seis meses. Após esse período, foi medida a área foliar e, posteriormente, as plântulas foram divididas em folha, caule e raiz, para obtenção da massa seca. Os resultados revelam que o melhor desenvolvimento de C. latiloba tem forte relação com a alta disponibilidade de luz, quando a planta apresentou melhores condições quanto aos parâmetros de trocas gasosas e crescimento, entretanto, independente do tratamento, esta espécie investiu biomassa em altura (alongamento do caule) e promoveu maior troca foliar. Já a eficiência quântica foi menor sob muita luz e maior na ausência de inundação. Quanto a P. glomerata, os dados demonstram que esta espécie é mais afetada pela inundação, com decréscimos do desempenho nos parâmetros de trocas gasosas e eficiência quântica. P. glomerata demonstrou outra estratégia de crescimento, diminuindo o investimento em altura e mantendo as suas folhas. Os resultados demonstraram que a espécie pioneira, mais abundante em baixas altitudes de áreas alagáveis, apresenta eficiente estratégia para seu estabelecimento, como alta produção de raízes adventícias, a fim de manter o metabolismo durante longo tempo de inundação, e respostas fisiológicas e morfológicas favoráveis a ambientes com alta luminosidade. Já a espécie secundária tardia demonstrou uma alta relação da redução do metabolismo com a inundação, o que pode decorrer da ativação do metabolismo anaeróbico. A fase aquática, somatório da inundação e pouca luz para plântulas de áreas alagáveis, caracteriza um ambiente temporariamente desfavorável. Para tolerar esse período, C. latiloba e P. glomerata apresentam respostas ecofisiológicas que justificam o seu estabelecimento para as condições impostas pelo pulso de inundação

Growth of Pouteria glomerata (Sapotaceae), a tree species from the Central Amazonian floodplain, under long-term flooding

To understand the occurrence of P. glomerata in the Amazonian várzea we investigated the morpho-physiological responses to long-term flooding. Seedlings of P. glomerata were subjected to two flooding treatments (partial and total) for six months. Following flooding treatments, we examined light-saturated photosynthesis (A), the potential quantum yield of photosystem II (inferred as the Fv/Fm ratio), height, number of leaves (NF), stem diameter at the base of the plant (DCC), leaf area and plant biomass. We found a decrease in gas exchange parameters and growth rates, whereas leaf damage increased with flooding. After six months of flooding, leaf area, and the total plant biomass as well as the biomass of the vegetative organs (leaf, stem and root) were lower in flooded seedlings than in control, non-flooded plants. As flooding level increased assimilated carbon was mainly allocated to stems. However, flooding treatments had no significant effect on specific leaf area, the root/shoot ratio and dry mass of roots. Totally submerged roots of flooded seedlings were strongly affected, showing to be the most critical condition for maintenance of physiological metabolism. P. glomerata was affected by long-term flooding. Thus, P. glomerata exhibited adjusts morpho-fisiological which makes it possible for this species to occur in the Amazon floodplain forest.Para entender a ocorrência de P. glomerata na várzea amazônica, investigamos as respostas morfo-fisiológicas a longo período de inundação. Durante seis meses, plântulas de P. glomerata foram submetidas a dois tratamentos de inundação (parcial e total) para análise da assimilação fotossintética líquida (A), eficiência quântica do fotosistema II (referido como Fv/Fm), altura, número de folhas, diâmetro do colo do caule (DCC), área foliar e biomassa da planta. Encontramos um decréscimo da atividade de trocas gasosas, das taxas de crescimento e danos foliares com o aumento do nível de inundação. Após seis meses de experimento, a área foliar, a biomassa dos órgãos vegetativos (raiz, caule e folha) e a biomassa total das plântulas inundadas foram menores que das plântulas controle, plântulas não-inundadas. De acordo com o aumento do nível de inundação, a biomassa fotoassimilada foi alocada principalmente para o caule. Somente área foliar específica, razão raiz / parte aérea e massa seca de raiz não apresentaram diferenças entre os tratamentos. As plântulas totalmente inundadas foram fortemente comprometidas, demonstrando ser esta à condição mais crítica para a manutenção do metabolismo fisiológico. P. glomerata foi afetada pelo longo período de inundação, no entanto a espécie revela adaptações morfo-fisiologica que justifica a sua ocorrência em florestas de várzea

Physiological responses to flooding and light in two tree species native to the Amazonian floodplains

In Amazonian floodplains, plant survival is determined by adaptations and growth strategies to effectively capture sunlight and endure extended periods of waterlogging. By measuring gas exchange, quantum efficiency of photosystem 2 (PSII), and growth parameters, we investigated the combined effects of flooding gradients and light on two common evergreen floodplain tree species, the light-tolerant Cecropia latiloba and the shade-tolerant Pouteria glomerata. Individual plants were subjected to different combinations of light and flooding intensity in short-term and long-term experiments. Plants of C. latiloba lost all their leaves under total submersion treatments (plants flooded to apex and with reduced irradiance) and showed highest maximum assimilation rates (A max) in not flooded, high light treatments (6.1μmolCO 2m -2s -1). Individuals of P. glomerata showed similar patterns, with A max increasing from 1.9μmolCO 2m -2s -1 under total flooding to 7.1μmolCO 2m -2s -1 in not flooded, high light treatments. During the long-term flooding experiment, quantum efficiency of PSII (F v/F m) of C. latiloba was not affected by partial flooding. In contrast, in P. glomerata F v/F m decreased to values below 0.73 after 120 days of total flooding. Moreover, total submergence led P. glomerata to reduce significantly light saturation point (LSP), as compared to C. latiloba. For both species morphological adjustments to long-term flooding, such as the production of adventitious roots, resulted in reduced total biomass, relative growth rate (RGR) and leaf mass ratio (LMR). Growth increase in C. latiloba seemed to be more limited by low-light than by flooding. Therefore, the predominant occurrence of this species is in open areas with high light intensities and high levels of inundation. In P. glomerata flooding induced high reductions of growth and photosynthesis, whereas light was not limiting. This species is more abundant in positions where irradiance is reduced and periods of submergence are slightly modest. We could show that the physiological requirements are directly responsible for the flooding (C. latiloba) and shade (P. glomerata) tolerance of the two species, which explains their local distribution in Amazonian floodplain forests. © 2011 Elsevier B.V

Considerations on extinct species of Brazilian flora

AbstractExtinction risk assessments are important tools for plant conservation. However, misinterpretations can lead to negative consequences for survival of species. Inconsistent categorization as extinction, when the species is still extant, constitutes a Romeo error, and annuls all and any mechanism of existing legal protection. But precisely determining the extinction of a plant species is a challenging task, in that the plants can portray characteristics that permit survival in a state of dormancy. To circumvent this problem, specialists frequently adopt precaution and a comprehensive approach that consider biological, ecological, and geographical parameters as inputs for the assessments. It is also important to include explicit logic arguments, as building-blocks of the rational that will support the assessment. Transparent interpretation of the available data can minimize inconsistent categorization. In Brazil, 23% of the plant species assessed as Extinct or Extinct in the Wild, comprise Romeo errors. The other 77% are cases of Data Deficient. Countries that succeeded in minimizing problems arising from this error developed specific legislation to protect threatened species, including mechanisms to annul an erroneous categorizations. Anyhow, the use of categories Extinct (EX) and Extinct in the Wild (EW) according to IUCN definitions should be avoided when no effort has been made to provide evidence of extinction in the wild