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Title: Effects of salinity and irradiance conditions on the growth, morphology and chemical composition of submersed aquatic macrophytes
Authors: University of Southwestern Louisiana. Department of Biology.
Aquatic Plant Control Research Program (U.S.)
Twilley, Robert Reece, 1952-
Barko, John W.
Keywords: Epiphytes
Ion exclusion
Myriophyllum spicatum
Tissue nutrients
Vallisneria americana
Aquatic plants
Aquatic weeds
Issue Date: Jul-1990
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: The growth, morphology, and chemical composition of Hydrilla verticillata, Myriophyllum spicatum, Potamogeton perfoliatus, and Vallisneria americana were compared among different salinity and light conditions. Plants were grown in microcosms (1.2 m³) under ambient photoperiod adjusted to 50 and 8 percent of solar radiation. The culture solution in five pairs ot tanks was gradually adjusted to salinities of 0, 2, 4, 6, and 12 ppt. With the exception of H. verticillata, the aquatic macrophytes examined may be considered eurysaline species that are able to adapt to salinities one third the strength of seawater. With increasing salinity, the inflorescence production decreased in M. spicatum and P. perfoliatus, yet asexual reproduction in the latter species by underground buds remained constant. Stem elongation increased in response to shading in M. spicatum, while shaded P. perfoliatus had higher concentrations of chlorophyll α. In association with high epiphytic mass, chlorophyll α concentrations in all species were greatest at 12 ppt. The concentration of sodium increased in all four species of aquatic macrophytes examined here, indicating that these macrophytes did not possess mechanisms to exclude this ion. The nitrogen content (Y) of the aquatic macrophytes tested increased significantly with higher sodium concentration (X), suggesting that nitrogen may be used in osmoregulation (Y = X * 0.288 + 6.10, r² = 0.71). The tolerance of V. americana and P. perfoliatus to salinity was greater in this study than in other investigations. This may be associated with experimental methodology, whereby macrophytes were subjected to more gradual rather than abrupt changes in salinity. Myriophyllum spicatum and V. americana, the two macrophytes that adapted best to the estuarine conditions in this study, as shown by growth under salinity up to 12 ppt, also exhibited a greater degree of response in morphology, tissue chemistry (including chlorophyll content and total nitrogen), and reproductive output in response to varying salinity and light conditions.
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