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首页> 美国卫生研究院文献>PLoS Clinical Trials >Effects of experimental nitrogen fertilization on planktonic metabolism and CO2 flux in a hypereutrophic hardwater lake
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Effects of experimental nitrogen fertilization on planktonic metabolism and CO2 flux in a hypereutrophic hardwater lake

机译：氮肥对富营养硬水湖浮游生物代谢和CO2通量的影响

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Hardwater lakes are common in human-dominated regions of the world and often experience pollution due to agricultural and urban effluent inputs of inorganic and organic nitrogen (N). Although these lakes are landscape hotspots for CO2 exchange and food web carbon (C) cycling, the effect of N enrichment on hardwater lake food web functioning and C cycling patterns remains unclear. Specifically, it is unknown if different eutrophication scenarios (e.g., modest non point vs. extreme point sources) yield consistent effects on auto- and heterotrophic C cycling, or how biotic responses interact with the inorganic C system to shape responses of air-water CO2 exchange. To address this uncertainty, we induced large metabolic gradients in the plankton community of a hypereutrophic hardwater Canadian prairie lake by adding N as urea (the most widely applied agricultural fertilizer) at loading rates of 0, 1, 3, 8 or 18 mg N L-1 week-1 to 3240-L, in-situ mesocosms. Over three separate 21-day experiments, all treatments of N dramatically increased phytoplankton biomass and gross primary production (GPP) two- to six-fold, but the effects of N on autotrophs plateaued at ~3 mg N L-1. Conversely, heterotrophic metabolism increased linearly with N fertilization over the full treatment range. In nearly all cases, N enhanced net planktonic uptake of dissolved inorganic carbon (DIC), and increased the rate of CO2 influx, while planktonic heterotrophy and CO2 production only occurred in the highest N treatments late in each experiment, and even in these cases, enclosures continued to in-gas CO2. Chemical effects on CO2 through calcite precipitation were also observed, but similarly did not change the direction of net CO2 flux. Taken together, these results demonstrate that atmospheric exchange of CO2 in eutrophic hardwater lakes remains sensitive to increasing N loading and eutrophication, and that even modest levels of N pollution are capable of enhancing autotrophy and CO2 in-gassing in P-rich lake ecosystems.
机译：硬水湖在世界上以人类为主的地区很常见，并且由于农业和城市污水中无机和有机氮（N）的输入而经常遭受污染。尽管这些湖泊是CO2交换和食物网碳（C）循环的景观热点，但氮富集对硬水湖食物网功能和碳循环模式的影响仍不清楚。具体而言，尚不清楚不同的富营养化情景（例如适度的非点源与极端点源）是否会对自养和异养C循环产生一致的影响，或者生物反应如何与无机C系统相互作用以形成空气-水二氧化碳的反应交换。为了解决这种不确定性，我们通过以0、1、3、8或18 mg NL <的负载量添加N作为尿素（应用最广泛的农业肥料），在高富营养硬水加拿大大草原湖的浮游生物群落中诱导了较大的代谢梯度。 sup> -1 周 -1 至3240-L，原位包膜。在三个独立的为期21天的实验中，所有处理N的方法均使浮游植物的生物量和初级总产值（GPP）显着提高了2到6倍，但N对自养生物的影响稳定在约3 mg NL -1 。相反，在整个处理范围内，异养代谢随着氮肥的施用而线性增加。在几乎所有情况下，N都会增加溶解性无机碳（DIC）的净浮游生物摄取，并增加CO2的流入速度，而浮游生物异养和CO2的产生仅发生在每个实验后期的最高N处理中，即使在这些情况下，外壳继续产生气体中的二氧化碳。还观察到方解石沉淀对CO2的化学作用，但同样没有改变净CO2通量的方向。综上所述，这些结果表明，富营养化硬水湖泊中的大气CO2交换对增加的氮负荷和富营养化仍然很敏感，即使适度的氮污染水平也能够增强富磷湖泊生态系统中的自养能力和二氧化碳的释放。

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