Effect of global change variables on the structure and photosynthesis of phytoplankton communities was evaluated in three different sites of the Patagonian coast of Argentina: enclosed bay (Puerto Madryn, PM), estuarine (Playa Unión, PU), and open waters (Isla Escondida, IE). We exposed samples to two contrasting scenarios: Present (nutrients at in situ levels) vs. Future (with lowered pH and higher nutrients inputs), and determined growth and photosynthetic responses after 2 days of acclimation. Under the Future condition phytoplankton growth was higher in the estuarine site compared to those in PM and IE. This effect was the most pronounced on large diatoms. While the increase of photosynthetic activity was not always observed in the Future scenario, the lower photosynthetic electron requirement for carbon fixation (Φ_e,C = ETR/P_m^B) in this scenario compared to the Present, suggests a more effective energy utilization. Long-term experiments were also conducted to assess the responses along a 4 days acclimation period in PU. Diatoms benefited from the Future conditions and had significantly higher growth rates than in the Present. In addition, Φ_e,C was lower after the acclimation period in the Future scenario, compared to the Present. Our results suggest that the availability, frequency and amount of nutrients play a key role when evaluating the effects of global change on natural phytoplankton communities. The observed changes in diatom growth under the Future scenario in PU and IE and photosynthesis may have implications in the local trophodynamics by bottom up control.

在阿根廷巴塔哥尼亚海岸的三个不同地点评估了全球变化变量对浮游植物群落结构和光合作用的影响：封闭湾（Puerto Madryn，PM），河口（PlayaUnión，PU）和开阔水域（Isla Escondida， IE）。我们将样本暴露于两种截然不同的场景：原位水平）与未来（较低的pH值和较高的养分输入），以及适应2天后确定的生长和光合作用响应。在未来条件下，与PM和IE相比，河口地区浮游植物的生长更高。这种效应在大型硅藻上最为明显。虽然在未来情景中并不总是观察到光合作用活性的增加，但是碳固定所需的光合作用电子的需求较低（Φ_电子 = ETR / P_米^乙）与目前相比，在这种情况下，表明能源利用效率更高。还进行了长期实验，以评估PU适应4天后的反应。硅藻受益于“未来”条件，其增长率远高于“现在”。此外，Φ_电子与当前相比，在“未来”方案中的适应期之后更低。我们的结果表明，在评估全球变化对天然浮游植物群落的影响时，养分的可用性，频率和数量起着关键作用。在PU和IE的Future情景下观察到的硅藻生长变化以及光合作用可能通过自下而上的控制对局部营养动力学产生影响。