To examine the effect of different growth forms of Sparganium erectum (Sparganiaceae) on its sediment trapping and retention characteristics, the plant phenology and morphological attributes based on stands along the edge of a river channel, river flow velocity distribution and sedimentation rates in-and outside the stands of a downstream site were examined over a 3-year period. A decomposition experiment was carried out to determine the respective fragmentation rates of S. erectum shoots and rhizomes. The preliminary monitoring revealed that S. erectum shoots attained distinct phonological stages; submerged in winter, subsequently emerging in late-spring, while the same cycle was followed by successive secondary cohorts. Our results highlighted that the growth form substantially affected the flow condition in-and outside the stands, thus affecting associated sedimentation rates. Although the sedimentation was high if the shoots were submerged in early-spring, the accumulated fine sediment layer was unleashed following shoot emergence, despite their large biomass and the resulting low flow velocity. The collapse of S. erectum shoots accelerated sedimentation again by increasing constriction to flow, producing a more preferable habitat for its soft roots and rhizomes. The collapse of emergent shoots, therefore, appeared to be a vital part of the inherent phonological cycle of S. erectum. Further, due to the high-decomposition rate, the collapsed shoots disappeared within 40-60 days, whereas the decomposed materials occupied a large fraction of the floating organic matter. The collapse of shoots increased flow resistance by $50%, though the stand area occupied a mere one-fifth of the channel. The seasonal observations provided further insight into the modification of flows due to the growth and changing growth form affecting associated fine sediment trapping and retention characteristics within the stands, deriving important management implications and highlighting the role of S. erectum as an ecosystem engineer in lowland streams.

The effect of harvesting the aboveground biomass on the growth of Phragmites australis in the subsequent growing season was investigated following cutting in June or July. Seasonal changes in rhizome biomass and total nonstructural carbohydrate (TNC) in seven age categories, from newly formed to six-years-old, were monitored for the two treatment stands and a control stand. The growth of the stands, as indicated by the aboveground biomass, showed a significant decline due to cutting in June but did not show a significant difference due to cutting in July, compared to that of the control stand. The timing of harvesting of aboveground biomass affected the annual rhizome resource allocation. A similar trend was observed for the pattern of resource allocation, as described by biomass variation of different rhizome-age categories for July-cut and control stands. However, the biomass of June-harvested rhizome categories tended to be smaller than the other two stands, indicating substantially reduced resource storage as a direct result of harvesting the aboveground biomass during the previous growing season. This implies that cutting of aboveground biomass in June is a better option for control of P. australis stands than cutting later in summer.

Quantitative studies of material budgets and resource allocation patterns of emergent plants are needed to fully understand nutrient and carbon cycling in wetlands. Whole-plant translocation patterns of nonstructural carbohydrates and synthesis of structural carbon were documented using two (shallow and deepwater) populations of Typha angustifolia in floodplain habitats of the Arakawa River, Japan. Monthly and bimonthly measurements of the concentrations of total carbon, non-structural carbohydrates, and water-soluble carbohydrates, as well as, estimates of standing stocks of aboveground (AG) and belowground (BG) biomass for both populations from 2002 to 2004 are described here. Annual patterns of carbon gain, rates of carbohydrate translocation between AG and BG organs, and rates of synthesis of structural carbon were estimated. Upward translocation supported all AG production for approximately 30 days. Afterward, the fraction of AG production supported by upward translocation decreased linearly with time, and completely diminished by Day 80 (counted from first day of growth; March 15). At Day 80, material translocation was directed downward and the percentage of downward translocation relative to AG net production increased until Day 170; there was a vigorous increase in downward translocation prior to senescence. In early summer (Day 80-110), more than half of the translocated materials were transformed into structural components, but by Day 125 only 30% was synthesized into total structural carbohydrates. Prior to senescence, there was a greater percentage of nonstructural carbohydrates in the rhizomes. Across the growing season (Day 60-153), the total amount of downward translocation was found to be proportional to AG production and the quantitative evaluation of the carbon budget shed further insight into the translocation process of this rhizomatous aquatic plants. In addition, insights on the differences between shallow and deepwater populations were gained. Especially, the deepwater population supported a higher fraction of vertical rhizomes compared to individuals sampled from the shallow water population.

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