Donghu Experimental Station of Lake Ecosystems, State Key Laboratory for Freshwater Ecology and Biotechnology of China, Institute of Hydrobiology, The Chinese Academy of Sciences, Donghu South Road 7, Wuhan 430072, People's Republic of China.
Chemosphere. 2013 Sep;93(2):373-9. doi: 10.1016/j.chemosphere.2013.04.100. Epub 2013 Jun 10.
Increased ammonium (NH4-N) concentrations in water bodies have been reported to adversely affect the dominant species of submersed vegetation in meso-eutrophic waters worldwide. However calcareous plants were lowly sensitive to NH4-N toxicity. In order to make clear the function of calcification in the tolerance of calcareous plants to NH4-N stress, we studied the effects of increased HCO3(-) and additional NH4-N on calcification and utilization of dissolve inorganic carbon (DIC) in Chara vulgaris Linn in a 7-d sub-acute experiment (light:dark 12:12h) carried out in an open experimental system in lab. Results revealed that calcification was dependent of utilization of dissolve inorganic carbon. Additional HCO3(-) significantly decreased the increase of pH while additional NH4-N did not. And additional HCO3(-) significantly improved calcification while NH4-N did in versus in relation to the variation of DIC concentration. However, addition of both HCO3(-) and NH4-N increased utilization of DIC. This resulted in calcification to utilization of DIC ratio decreased under additional NH4-N condition while increased under additional HCO3(-) conditions in response to the variation of solution pH. In the present study, external HCO3(-) decreased the increase of solution pH by increasing calcification, which correspondingly mitigated the toxic effect of high NH4-N. And we argue that the mitigating effect of increased HCO3(-) on NH4-N toxicity is dependent of plant calcification, and it is a positive feedback mechanism, potentially leading to the dominance of calcareous plants in meso-eutrophic water bodies.
水体中铵（NH4-N）浓度的增加已被报道会对世界各地中营养型水体中沉水植被的优势物种产生不利影响。然而，钙质植物对 NH4-N 毒性的敏感性较低。为了明确钙化在钙质植物耐受 NH4-N 胁迫中的作用，我们在实验室的开放实验系统中进行了为期 7 天的亚急性实验（光照：黑暗 12:12h），研究了增加 HCO3(-)和额外 NH4-N 对普通轮藻钙化和溶解无机碳（DIC）利用的影响。结果表明，钙化依赖于 DIC 的利用。额外的 HCO3(-)显著降低了 pH 的升高，而额外的 NH4-N 则没有。此外，HCO3(-)的添加显著改善了钙化，而 NH4-N 则没有，这与 DIC 浓度的变化有关。然而，同时添加 HCO3(-)和 NH4-N 增加了 DIC 的利用。这导致在额外 NH4-N 条件下，钙化对 DIC 利用的比值下降，而在额外 HCO3(-)条件下则增加，以响应溶液 pH 的变化。在本研究中，外部 HCO3(-)通过增加钙化来降低溶液 pH 的升高，从而相应地减轻了高 NH4-N 的毒性作用。我们认为，增加 HCO3(-)对 NH4-N 毒性的缓解作用依赖于植物的钙化，这是一种正反馈机制，可能导致钙质植物在中营养型水体中占据优势。
