Photoacclimation in a tropical population of Cladophora glomerata (L.) Kützing 1843 (Chlorophyta) from southeastern Brazil

Photoacclimation of photosynthesis was investigated in a tropical population of C. glomerata (São Paulo State, southeastern Brazil, 20º 48’ 24" S and 49º 22’ 24" W) by chlorophyll fluorescence parameters and chlorophyll a content. Plants were acclimated to two levels of irradiance: low (65 ± 5 µmol.m-2.s-1) and high (300 ± 10 µmol.m-2.s-1) and exposed short-term (4 days) and long-term (28 days) under a light-dark cycle of 12:12 hours. Photosynthesis-irradiance (PI) curves revealed distinct strategies of photoacclimation. In long-term exposure, plants acclimated by altering the photosynthetic units (PSU) number and keeping fixed the PSU size, revealed by increased rates of maximum photosynthesis (Pmax), lower photosynthetic efficiency (alpha) and higher values of the saturation parameter (Ik) under high irradiance. The short-term acclimation strategy consisted of changing the PSU size, with a fixed number of PSUs, as revealed by similar Pmax but higher alpha and lower Ik under low irradiance. Chlorophyll a contents followed the general pattern reported in green algae of higher concentrations under lower irradiance. Dark/light induction curves revealed consistently higher values of potential quantum yield under low irradiance. Initial and final values showed a higher recovery capacity in the short (84.4-90.6 percent) term exposure than in the long-term case (81.4-81.5 percent). ETR (electron transport rate) and NPQ (non-photochemical quenching) values were consistently higher under low irradiance. ETR showed a continuous and steady increase along the light exposure period in the short and long-term experiments, whereas NPQ values revealed a rapid increase after 15 seconds of light exposure, kept a slightly increasing trend and stabilized in most treatments. Lower photosynthetic performance (ETR) and recovery capacity of potential quantum yield were observed, particularly in long-term exposure, suggesting that this population...

A fotoaclimatação da fotossíntese foi investigada numa população tropical de Cladophora glomerata (Estado de São Paulo, sudeste do Brasil, 20º 48’ 24" S e 49º 22’ 24" W) através de parâmetros de fluorescência da clorofila e conteúdo de clorofila a. As plantas foram aclimatadas a dois níveis de irradiância: baixa (65 ± 5 µmol.m-2.s-1) e alta (300 ± 10 :mol.m-2.s-1) e expostas a curto período (4 dias) e longo período (28 dias) em fotoperíodo de 12 horas. Curvas de fotossíntese-irradiância (FI) revelaram estratégias distintas de fotoaclimatação. Plantas expostas a longo período aclimataram pela alteração do número de unidades fotossintéticas (UF) e mantiveram fixo o tamanho das UF. Estas características foram reveladas por menores taxas de fotossíntese máxima (Fmax), menor eficiência fotossintética (alfa) e valores mais altos do parâmetro de saturação (Ik) em alta irradiância. A estratégia de aclimatação em curto período consistiu em mudança no tamanho das UF, com número fixo de UF, conforme revelado por taxas semelhantes de fotossíntese máxima (Fmax), maiores valores de alfa e menores de Ik em baixa irradiância. Os conteúdos de clorofila a seguiram o padrão geral reportado para algas verdes de maiores concentrações em baixa irradiância. Curvas de indução escuro/luz revelaram valores consistentemente mais elevados de rendimento quântico potencial em baixa irradiância. Valores iniciais e finais mostraram capacidade de recuperação mais elevada em curto período (84,4-90,6 por cento) do que em longo período (81,4-81,5 por cento). Os valores da taxa de transporte de elétrons (ETR) e extinção não-fotoquímica (NPQ) foram consistentemente mais elevados em baixa irradiância. Os valores de ETR tiveram aumento contínuo e estável ao longo do período de exposição luminosa em curto e longo períodos, enquanto que os de NPQ revelaram aumento rápido após 15 seconds de exposição à luz, mantiveram leve tendência de aumento e então estabilizaram...

Ecological distribution of stream macroalgal communities from a drainage basin in the Serra da Canastra National Park, Minas Gerais, Southeastern Brazil

Twelve stream segments were sampled four times in 1998-1999 (one sampling per season) in the drainage basin of the upper São Francisco River (19º45'-21º25'S, 49º05'-51º30'W), situated in Serra da Canastra National Park, at altitudes ranging from 1,175 to 1,400 m. The macroalgae survey resulted in 30 species, with a predominance of Cyanophyta (12 species = 40 percent) and Chlorophyta (11 species = 36.5 percent) and a lower proportion of Rhodophyta (seven species = 23.5 percent). Two species, Klebsormidium rivulare (Chlorophyta) and Kyliniella latvica (Rhodophyta), were new records for Brazil. Capsosira sp. and Stigonema sp. (Cyanophyta) and the "Chantransia" stage of Batrachospermum (Rhodophyta) were the most widespread macroalgae, occurring in six sampling sites, whereas 11 species were found at only one site. The proportion of macroalgal morphological types were as follows: mats (33 percent), free filaments (27 percent), gelatinous filaments (27 percent), crusts (7 percent), tufts (3 percent), and gelatinous colonies (3 percent). The flora revealed few species in common (4 percent-8 percent) with stream macroalgae from other Brazilian regions. The macroalgal communities proved to have species richness values close to the highest values reported in previous studies. The patterns typical for stream macroalgal communities (patchy distribution and dominance of few species) were also found in this basin. However, the stream variables most influential in macroalgal distribution in this study (rocky substratum, low pH, high COD, water color, and current velocity) were essentially the same that best describe the limnological characteristics of this lotic ecosystem. In addition, this combination of variables differed sharply from results of previous studies in other Brazilian stream ecosystems.