Physiological Responses of Transplants of the Freshwater Angiosperm Vallisneria americana along a Salinity Gradient in the Caloosahatchee Estuary (Southwestern Florida)

• Published in: Estuaries Vol. 22; no. 1; pp. 138 - 148
• Main Authors: Kraemer, George P., Chamberlain, Robert H., Doering, Peter H., Steinman, Alan D., Hanisak, M. Dennis
• Format: Journal Article
• Language: English
• Published: Lawrence, KS Estuarine Research Federation 01.03.1999; Springer Nature B.V
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Aquatic plants; Autoecology; Biological and medical sciences; Brackish; Carbohydrates; Dry season; Dry seasons; Estuaries; Fresh water; Freshwater; Freshwater ecology; Fundamental and applied biological sciences. Psychology; Marine; Nitrogen; Photosynthesis; Physiological responses; Physiology; Plants; Plants and fungi; Rainy season; Rainy seasons; Salinity; Seasons; Tissue samples; Tissue transplantation; Transplantation; Upstream; Vallisneria americana; Florida; United States; North America; America; ASW, USA, Florida, Caloosahatchee Estuary; Physiological condition; Brackish water environment; Gradient; Temperature; Fresh water; Estuaries; Environmental factor; Transplantation; Survival; Salinity; Light; Angiospermae; Spermatophyta; Aquatic plant
• ISSN: 0160-8347; 1559-2723; 1559-2758; 1559-2731
• DOI: 10.2307/1352934

Fluctuations in freshwater input may affect the physiology and survival of submerged aquatic vegetation (SAV) occurring in oligoaline to mesohaline estuarine regions. Controls on the distribution of the freshwater angiosperm Vallisneria americana, were investigated by transplanting ramets. Pots (3.8-1) containing ramets were distributed among four sites (upstream site [least saline], donor site, near downstream site, and far downstream site [most saline]) in the Caloosahatchee Estuary (Southwest Florida) during wet (May-August) and dry (October-February) seasons. During 2-4 mo of each season, physiological indicators were monitored, including photosynthesis, glutamine synthetase activity, and protein content in shoots, and carbohydrates and total nitrogen and carbon in shoot and subterranean tissues. Where the physical environment (light or salinity) was suboptimal, all physiological indices, except photosynthetic rate, showed similar stress responses, which ranged from a slow decline to a rapid drop in physiological function. Levels of soluble carbohydrates decreased in response to unfavorable conditions more rapidly than did insoluble carbohydrates. Shoot protein of V. americana declined prior to transplant death, suggesting that measuring protein content may provide a rapid assessment of physiological health. V. americana transplants at the low-salinity upstream site died during both wet and dry season experiments, likely in response to light limitation and/or partial burial by sediments. At the far downstream site, death occurred within 2-4 wk, and was attributable to elevated salinities (> ca. 15 ‰). Comparison of physiological responses with salinity and light regimes at the donor and near downstream sites suggest that light may ameliorate salinity stress. This study demonstrates that V. americana, nominally classed as a freshwater macrophyte, is capable of a remarkable degree of halotolerance.