CIMAR/CIIMAR-Centro Interdisciplinar de Investigação Marinha e Ambiental, Universidade do Porto, Rua dos Bragas, 289, 4050-123, Porto, Portugal,
Environ Sci Pollut Res Int. 2014 Sep;21(17):10270-8. doi: 10.1007/s11356-014-2953-1. Epub 2014 May 3.
The fate of excess nitrogen in estuaries is determined by the microbial-driven nitrogen cycle, being denitrification a key process since it definitely removes fixed nitrogen as N2. However, estuaries receive and retain metals, which may negatively affect this process efficiency. In this study, we evaluated the role of salt marsh plants in mediating cadmium (Cd) impact on microbial denitrification process. Juncus maritimus and Phragmites australis from an estuary were collected together with the sediment involving their roots, each placed in vessels and maintained in a greenhouse, exposed to natural light, with tides simulation. Similar non-vegetated sediment vessels were prepared. After 3 weeks of accommodation, nine vessels (three per plant species plus three non-vegetated) were doped with 20 mg/L Cd(2+) saline solution, nine vessels were doped with 2 mg/L Cd(2+) saline solution and nine vessels were left undoped. After 10 weeks, vessels were dissembled and denitrification potential was measured in sediment slurries. Results revealed that the addition of Cd did not cause an effect on the denitrification process in non-vegetated sediment but had a clear stimulation in colonized ones (39 % for P. australis and 36 % for J. maritimus). In addition, this increase on denitrification rates was followed by a decrease on N2O emissions and on N2O/N2 ratios in both J. maritimus and P. australis sediments, increasing the efficiency of the N2O step of denitrification pathway. Therefore, our results suggested that the presence of salt marsh plants functioned as key mediators on the degree of Cd impact on microbial denitrification.
河口中过量氮的命运由微生物驱动的氮循环决定，反硝化作用是一个关键过程，因为它可以将固定氮绝对转化为 N2。然而，河口会接收并保留金属，这可能会降低这个过程的效率。在这项研究中，我们评估了盐沼植物在调节镉（Cd）对微生物反硝化过程的影响方面的作用。从河口采集了互花米草（Juncus maritimus）和芦苇（Phragmites australis），连同涉及它们根部的沉积物，每种植物都放在容器中，在温室中保持，暴露在自然光下，并模拟潮汐。还准备了类似的无植被沉积物容器。适应 3 周后，用 20mg/L 的 Cd(2+)盐水溶液对 9 个容器（每种植物 3 个加 3 个无植被）进行掺杂，用 2mg/L 的 Cd(2+)盐水溶液对 9 个容器进行掺杂，用 9 个未掺杂的容器作为对照。10 周后，拆开容器并测量沉积物悬浮液中的反硝化潜力。结果表明，Cd 的添加对无植被沉积物中的反硝化过程没有影响，但对已定植的沉积物有明显的刺激作用（芦苇为 39%，互花米草为 36%）。此外，这种反硝化速率的增加伴随着 N2O 排放量和两种植物的 J. maritimus 和 P. australis 沉积物中的 N2O/N2 比值的降低，从而提高了反硝化途径中 N2O 步骤的效率。因此，我们的结果表明，盐沼植物的存在是影响 Cd 对微生物反硝化影响程度的关键因素。
