Elevated ammonium concentrations and low light form a dangerous synergy for eelgrass Zostera marina

Marine Ecology Progress Series

Fernando G. Brun¹  Morten F. Pedersen¹  Juan J. Vergara¹  Beatriz Villazaacuten¹ 

关键词: Dissolved inorganic nitrogen;    Light;    Nitrogen metabolism;    Carbon reserves;    Seagrass;    Eutrophication;   

DOI  :  10.3354/meps10517

学科分类：海洋学与技术

来源: Inter-Research

【 摘 要 】

ABSTRACT: We studied the effect of ecologically relevant ammonium concentrations and light on several morphological and physiological properties, nitrogen metabolism and carbon reserves of eelgrass Zostera marina L. Eelgrass was grown under mesocosm conditions at 3 levels of ammonium enrichment (target concentrations of 0, 10 and 25 µM) and 2 levels of light (low and high light). High ammonium supply combined with low light had a negative effect on several morphological and physiological response parameters, while no such effects were found when ammonium was supplied under high light. N enrichment caused an increase in the content of total N, intracellular ammonium, free amino acids and residual N in the plants and this response was more pronounced under low-light conditions than under high light. The soluble proteins content decreased, in contrast with external ammonium enrichment. The accumulation of free amino acids and residual N in NH₄⁺-enriched plants was followed by a substantial drop in carbohydrate reserves (sucrose and starch), which was larger in plants grown under low-light conditions. Our results indicate that N enrichment increases the demand for C skeletons and energy, and that photosynthesis cannot supply enough C and energy to cover that demand under low-light conditions. Eelgrass plants exposed to reduced light conditions, for example close to their depth limit or when covered by drift macroalgae, may thus be especially susceptible to enhanced ammonium concentrations. Our study demonstrates that ammonium toxicity may explain why eelgrass and other seagrasses deteriorate under nutrient-rich, low-light conditions.

【 授权许可】

Unknown