State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of the Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
Sci Total Environ. 2017 Dec 1;601-602:1513-1521. doi: 10.1016/j.scitotenv.2017.05.268. Epub 2017 Jun 9.
Loss of submersed macrophytes is a world-wide phenomenon occurring when shallow lakes become eutrophic due to excess nutrient loading. In addition to the well-known effect of phosphorus, nitrogen as a trigger of macrophyte decline has received increasing attention. The precise impact of high nitrogen concentrations is debated, and the role of different candidate factors may well change over the season. In this study, we conducted experiments with Vallisneria natans during the growing season (June-September) in 10 ponds subjected to substantial differences in nitrogen loading (five targeted total nitrogen concentrations: control, 2, 10, 20, and 100mgL) and compared the results with those obtained in our earlier published study from the low-growth season (December-April). Like in the low-growth season, growth of V. natans in summer declined with increasing ammonium (NH) concentrations and particularly with increasing phytoplankton chlorophyll a (Chla). Accordingly, we propose that shading by phytoplankton might be of key importance for macrophyte decline, affecting also periphyton growth as periphyton chlorophyll a (Chla) decreased with increasing Chla. Free amino acid contents (FAA) of plants tended to increase with increasing NH concentrations, while the relationships between FAA with growth indices were all weak, suggesting that FAA might be a useful indicator of the physiological stress of the plants but not of macrophyte growth. Taken together, the results from the two seasons indicate that although a combination of high nitrogen concentrations (ammonium) and shading by phytoplankton may cause severe stress on macrophytes, active growth in the growing season enabled them to partly overcome the stress.
浅水湖泊由于富营养化导致营养物质过剩，沉水植物大量消失是一种世界性的现象。除了众所周知的磷的影响外，氮作为沉水植物衰退的触发因素也受到了越来越多的关注。高氮浓度的确切影响仍存在争议，不同候选因素的作用在整个季节中很可能发生变化。在这项研究中，我们在 10 个池塘中进行了苦草的实验，这些池塘的氮负荷有很大差异（5 个目标总氮浓度：对照、2、10、20 和 100mgL），并将结果与我们之前在低生长季节（12 月至 4 月）发表的研究结果进行了比较。与低生长季节一样，苦草在夏季的生长随着铵（NH）浓度的增加而下降，特别是随着浮游植物叶绿素 a（Chla）的增加而下降。因此，我们提出浮游植物的遮蔽可能对沉水植物的衰退至关重要，这也影响了周丛藻类的生长，因为周丛藻类叶绿素 a（Chla）随着 Chla 的增加而减少。植物的游离氨基酸含量（FAA）随着 NH 浓度的增加而增加，而 FAA 与生长指数之间的关系都很弱，这表明 FAA 可能是植物生理压力的有用指标，但不是沉水植物生长的指标。综上所述，两个季节的结果表明，尽管高氮浓度（铵）和浮游植物的遮蔽可能会对沉水植物造成严重的压力，但在生长季节的活跃生长使它们能够部分克服这种压力。
