When Zostera marina is intermixed with Ulva, its photosynthesis is reduced by increased pH and lower light, but not by changes in light quality
(English)In: Aquatic Botany, ISSN 0304-3770Article in journal (Refereed) Submitted
In eutrophic coastal waters, seagrasses often become intermixed with opportunistic algae, such as different species of Ulva that grow on top of, or between shoots in Zostera marina beds. When this occurs, the algae can both reduce the amount of light reaching the seagrasses and also alter the quality of that light so that it becomes dominated by the green part of the spectrum. Since Ulva has an efficient photosynthetic carbon uptake, its photosynthesis can drastically increase the pH of the surrounding seawater, and thus create conditions where Zostera marina is unable to acquire inorganic carbon (Ci). To evaluate the effects of Ulva on the photosynthetic capacities of the temperate seagrass Zostera marina, we compared it in the laboratory under normal light and light filtered through layers of Ulva intestinalis, and repeated the experiments with the addition of pH-induced changes in carbon speciation and availability. One thallus of Ulva reduced photosynthetically available irradiance to underlying seagrass by about 50% and shifted the quality of remaining light towards the green part of the spectrum. Interestingly, there was no significant difference in photosynthetic performance between Zostera marina under normal light and under Ulva-filtered green light when adjusted to the same irradiance as for the control plants, indicating that the green spectrum transmitted through Ulva layers may be efficient in driving photosynthesis in the seagrass bed. On the other hand, algae-generated pH shifts had drastic negative effects on the photosynthesis of the seagrass.
Eutrophication, Inorganic carbon, Light quality, pH, Photosynthesis, Zostera marina
Research subject Plant Physiology
IdentifiersURN: urn:nbn:se:su:diva-55865OAI: oai:DiVA.org:su-55865DiVA: diva2:409103