Respuestas ecofisiológicas al enriquecimiento de amonio en angiospermas marinas

Anthropogenic nutrient loading in coastal areas is one of the major causes of seagrass decline worldwide. One of the main negative effects is indirectly caused by the proliferation of fast-growing species promoting light attenuation, sediment anoxia and sulphide intrusion risks. However, the parallel direct toxic effect caused by high ammonium (NH4+) concentrations on seagrasses has received little attention, in spite of some pioneer works. Adverse effects of NH4+ enrichment have been traditionally explained by internal accumulation of NH4+. To prevent toxic effects, plants must assimilate this nutrient into amino acids and other non-toxic organic compounds, generating strong internal demand for ATP and organic carbon skeletons, which must be provided by photosynthesis or from C-reserves. Thus, any factor affecting NH4+ uptake and/or assimilation could intensify or ameliorate NH4+ toxicity in seagrasses. This PhD Thesis studies the interactive effect of NH4+ enrichment and different environmental factors in the genus Zostera. In the first two chapters, the interaction between NH4+ and phosphate uptake rates and the interactive effect of light, hydrodynamics and NH4+ enrichment was studied in Z. noltei. In these assays ammonium was taken up following a diffusive trend, and while a shortcoming of phosphate uptake was found in leaves of Z. noltei when NH4+ was present, NH4+ uptake was unaffected by phosphate presence (chapter 1). As well, a non-linear response to NH4+ enrichment with flow velocity was recorded, with the strongest negative effect at intermediate flow (chapter 2). The effects of light and NH4+ on morphology, physiology, nitrogen metabolism and carbon reserves were studied in Z. marina (chapter 3). Light reduction had negative and synergistic effects with NH4+ enrichment, which were related with a drastic drop in carbon reserves and a remarkable increase in amino acid concentrations, indicating a tight coupling between carbon an nitrogen metabolisms. The response to the interaction between NH4+ loading and hyposaline stress was analyzed on different physiological and morphological properties of Z. marina (chapter 4). The negative and interactive effect between high NH4+ concentrations and low salinity was correlated with an increase in intracellular NH4+ content and a decrease in photosynthetic rates and non-structural carbohydrates, causing a drop in growth and survival of plants. Thus, hyposaline stress enforced the toxic effect of NH4+ by increasing the competition between ammonium assimilation and osmotic regulation for energy and C-skeletons. In summary, this Thesis highlights that toxic effects promoted by NH4+ on seagrasses can be intensified or alleviated depending in the presence of other natural stressors. In nature, organisms are rarely stressed by only one factor, and the interaction among multiple stressors may drive synergistic, antagonist or even non- linear responses. The understanding of nature of such interactions is important for developing better predictions and managing policies for seagrass ecosystems, since NH4+ load is expected to increase in the near future in coastal areas, jointly with the modification of a broad range of environmental factors as a consequence of the global change.

Author dc:creator

• Villazán Peñalosa, Beatriz

Advisors dc:contributor.advisor

• Vergara Oñate, Juan José
• Brun Murillo, Fernando Guillermo

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International
• info:eu-repo/semantics/openAccess

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10498/16760

OAI identifier oai:identifier

oai:rodin.uca.es:10498/16760