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The rhizome dynamics of Typha angustifolia in relation to water depth were investigated. Observations were made in two different stands, namely Akigase from April 2002 to December 2003, and Teganuma from April 2003 to December 2004. The mean rhizome length in the two stands was not significantly different but the mean rhizome diameter and biomass showed a significant difference. The larger rhizome diameter in Teganuma is seemingly an important adaptation to maintain effective aeration of the rhizome by reducing the internal resistance; while larger biomass helps survival under anoxia for longer periods of time, it also provides strong anchorage to the substrate. [ABSTRACT FROM AUTHOR]

The influence of Phragmites australis on the growth of Zizania latifolia, and the morphological characteristics of both species, were investigated at two nutrient levels. The experiment was carried out over three growing seasons between May 2003 and December 2005. The experimental plot was longitudinally divided into two equal halves, one of which was planted with Zizania latifolia (Zizania zone) and the other one with Phragmites australis (Phragmites zone). Four weeks after transplantation, the plot was again divided horizontally, perpendicular to the previous division, and subject to low (LN) and high nutrient (HN) treatments. Measured growth indices of the two species were more developed in the HN than in the LN treatments. Both species were observed to invade each other’s zone, but Phragmites latifolia seemed to out-compete Zizania latifolia individuals. This was evident from the decrease in below ground biomass of Zizania latifolia in the third growing season and deterioration in above ground organs with time. It was concluded that Phragmites australis out-competes Zizania latifolia due to better developed root and rhizome system. [ABSTRACT FROM AUTHOR]

A Japanese minnow, Pseudorasbora parva, was exposed simultaneously to multiple dangers in experimental tanks. The study aimed to quantify to what extent the risk of predation coinciding with an adverse environmental factor, high flow velocity, affects prey in terms of growth and energy expenditure. In this experiment, two measures of growth (i.e., body weight and length), condition, feeding, swimming cost and behavioral responses were analyzed. The results showed that in such an environment, prey showed lowered growth and were in a poorer condition. As the prey shifted to the shallow area with high flow velocity, the prey consumed a lower ration and incurred multiple costs for swimming locomotion that might reduce the allocation of energy to biomass and energy storage. Reduction in activity might decrease the cost of locomotion, but it did not have a considerable effect on overall swimming energy expenditure. In stream ecosystems, the high swimming energy expenditure appears to magnify the effects of predation risk by causing lowered growth and a poorer condition and, hence, fitness. The present study shows that high flow velocity is one of the environmental factors that determine the energetic responses of a potential prey to the presence of predators. [ABSTRACT FROM AUTHOR]

We investigated the relationships between the biomass of submersed aquatic plants (Potamogeton malaianus and Potamogeton oxyphyllus) and flow velocity, water depth, and organic matter in sediment in a fourth order stream in Japan. In spite of narrow ranges of current velocity (0-37 cm/s) and water depth (0-35 cm) in the study reach, plants were more abundant at moderate depth. Plant biomass was negatively correlated with water depth and water flow but positively correlated with organic matter content of the sediment. [ABSTRACT FROM AUTHOR]

The effects of increased salinity and cutting the above ground biomass on the growth of Phragmites australis were evaluated by investigating four experimental reed stands grown in outdoor tanks. Two stands were treated with 30‰ salinity and the other two stands with freshwater; one stand of each treatment was cut to 20 cm during the second growing season. Growth conditions were observed until all the plants were dead at the end of the second year. The number of shoots emerged from the freshwater-treated stand was about 70% higher than that of the saltwater-treated stand. The number of shoots emerged from cut plant stands were markedly lower than uncut stands. The average shoot height was negatively affected by salinity and shoots that emerged after cutting further decreased in height. The average number of leaves on a shoot was not significantly affected by salinity, but reduced by cutting in both treatments. Leaf length, width and the distance between leaves were decreased by both salinity and cutting. In the freshwater-treated uncut stand more than 50% of the shoots formed panicles, but this proportion was reduced to 6% by salinity, to 15% by cutting, and to 0% by the combination of salinity and cutting. This study showed again that salinity reduces the growth of aboveground components. The growth, however, was most severely retarded by cutting combined with salinity, which has many implications for better management of P. australis stands. [ABSTRACT FROM AUTHOR]

Direct evidence of epiphytic algal effects on the growth and production of freshwater submerged macrophytes is scarce. To obtain more reliable, quantitative data about this phenomenon, a laboratory experiment was carried out over 84 days in controlled conditions with the submerged macrophyte, Potamogeton perfoliatus. It was based on a 2×2 factorial design with two epiphytic conditions (with epiphytic algae and without) and two light conditions (high and low). Growth and production was investigated by measuring biomass, chlorophyll a concentration of leaves and net photosynthesis of the plants on Days 14, 28, 42, 70 and 84. The chlorophyll a concentration of epiphytic algae was also measured on these days. Morphological parameters of the plants were measured on Days 14, 30, 70 and 84. The chlorophyll a concentration of epiphytic algae increased significantly over the experimental period in both HLE (high light with epiphytic algae) and LLE (low light with epiphytic algae) treatments. Plants showed significant morphological changes in total shoot length, number of newly recruited shoots and expansion or contraction of the leaf surface area due to the epiphytic algal load and low light condition. The biomass (both above and below ground) and net photosynthesis rate was higher in high light than in the low light condition, but the chlorophyll a concentration was always higher in the low light condition than in the high light condition. In the plants without epiphytic algae, the chlorophyll a concentration, above ground biomass accumulation and net photosynthesis was significantly higher than in plants with epiphytic algae in both light conditions. The dead leaf dry matter was greater in the plants with epiphytic algae than in those without epiphytic algae in both light conditions. Therefore, epiphytic algae and low light phenomena both reduce growth and production. In general, plants tend to optimize low light-created shade by changing their physiology and morphology, but they could not respond to the same when epiphytic algae-created shade occurred on the leaf surface in the present experiment. [Copyright &y& Elsevier]