No abstract

Seasonality and composition of epipelic diatom community were studied for two years in two wetlands of Bangladesh namely, Joysagar and Sitlai Beel. A total 73 diatom taxa were recorded. The average density of epipelic diatom was higher in Sitlai Beel (52.97  10 4 /g sediment) than in the Joysagar (3.92 10 4 /g sediment). The epipelic diatom community of Joysagar was dominated by the species of Melosira, Synedra, Navicula, Pinnularia, Gomphonema, and Nitzschia, whereas Melosira, Navicula, Pinnularia, Cymbella and Gomphonema dominated in Sitlai Beel. Melosira granulata, Navicula americana, Pinnularia major, and Gomphonema lanceolatum were dominant and expressed distinct seasonality in both wetlands. The concentration of soluble reactive silicate of water and the average density of epipelic diatom did not express any significant relation in both of the water bodies. The concentration of phytoplankton chl a had a positive relationship with epipelic diatoms and was significant in Sitlai Beel.

Epiphyton might have distinctive influence on the morphology of substrate macrophyte. In this article, we evaluate the influence of epiphyton on the morphological characteristics of their substrate submerged macrophyte, Potamogeton perfoliatus under two light intensities. The experiment was carried out for a period of 84 days in 12 glass aquaria under laboratory conditions. It was based on a 2 9 2 factorial design with epiphyton status (present or absent) and light intensity (200 or 80 lE m -2 s -1 ). Both epiphyton and light intensity had significant effects on the morphology and biomass allocation of the experimental plants. The average number of leaves, total length of newly recruited shoots and diameter of stems were greater in the epiphyton-free control plants than in the epiphyton-colonized plants under low light conditions. The plants with epiphyton allocated more biomass in their rhizomes and roots (% relative to total biomass basis) when compared to the control plants in both light intensities. There were also significant epiphyton-light interactions. The control plants under low light intensity showed higher internodal elongation in their main shoots when compared to the plants under high light intensity as an adaptation mechanism. Whereas the plants with epiphyton did not show such an adaptation. The new shoots of the control plants under low light intensity did not show any internodal elongation as observed in the main shoots. Furthermore, the length of the leaves of main shoots was larger in control plants with epiphyton and high light intensity than in plants with epiphyton and low light intensity, but such a variation was absent in the new shoots. We conclude that the long-term colonization by epiphyton and their shading effects induced the observed morphological changes in plants.

The composition and distribution of epiphytic algae on Potamogeton perfoliatus were studied in a controlled laboratory environment over 84 days under two light conditions. The study was based on a 2 × 2 factorial design with two light conditions (high and low, 200 and 80 µE m-2 s-1) and two different plant parts (apical and basal). In both light conditions, the community consisted of 18 taxa (under nine genera) of Bacillariophyceae. Amphora lineolata, Cocconeis placentula, and Diatoma hiemale were the most common and abundant species. The total algal density was significantly higher in the high light condition and on the basal plant part than in the low light condition and on the apical plant part. At termination of the experiment, basal plant parts exhibited a more uniform crust of epiphytic algae consisting of c. 95% C. placentula whereas the apical plant parts expressed a more mosaic community (under both light conditions).

The morphological plasticity of the submerged macrophyte Potamogeton wrightii under different nutrient conditions and photoperiods was measured in a laboratory controlled experiment for 70 days in Japan. Six treatments were used in this experiment (3 × 2 factorial design with three replications) which consisted of three photoperiods and two nutrient conditions. Both photoperiod and nutrient condition had a pronounced effect on shoot and leaf morphology in P. wrightii. New shoot recruitment, and the length of main and new shoots gradually decreased with shortening photoperiod under both nutrient treatments. Plants under an 8 h photoperiod and high nutrient levels generated significantly more dead leaves (7.42 leaf·shoot −1 ) and decomposed shoots (1.3 shoots·pot −1 ) than plants under other treatments. Under short photoperiods (12 and 8 h) plants failed to produce flowering spikes in both nutrient conditions. In high nutrient conditions, P. wrightii produced shorter shoots, fewer leaves with shorter and narrower laminas, and smaller petioles compared with plants in the low nutrient condition. This may be adaptive under high nutrient conditions because it lowers foliar uptake and, thus, nutrient toxicity.