Phytoplankton photophysiology in lakes and oceans

浮游植物是自然水域中普遍存在的光合作用微生物；它们是水生生态系统的重要组成部分，因为它们构成了许多食物网的基础。它们包括令人难以置信的形状、大小和物种的多样性。当生态系统被人类影响改变时，特别是由于农业径流中营养物质的添加，以前并不丰富的浮游植物物种可能会繁殖。当这些物种是有害的(产生毒素)时，例如一些形成水华的蓝藻物种，饮用水或娱乐用水的质量可能会受到影响。 在我们的研究计划中，我们感兴趣的是了解为什么某些浮游植物物种在特定的时间存在，以及在哪些环境条件下它们是有利的。为此，我们部署了一个自主研究平台，使我们能够(在湖中使用复杂的“潜水显微镜”)跟踪物种及其食草动物(浮游动物)的时间，以及其他重要因素，如营养物质和光线。我们还旨在了解浮游植物群落的变化如何影响生态系统的其他部分。在接下来的几年里，我们将重点关注丰富的水生细菌的重要作用。 因为它们具有光合作用，就像陆地上的植物一样，一些植物适应强光环境(生长在地表附近)，另一些植物喜欢暗光。一些浮游植物可以很容易地适应从昏暗到强光的快速转换，但另一些则不能。在我们的计划中，我们将在实验室研究不同物种如何适应这些光照水平的变化，特别是他们在一天中的不同时间实现这种适应的效率。这样的研究将使我们能够创建适当的模型来估计未来浮游植物丰度和生产力的变化。 因为浮游植物吸收光线，我们可以使用卫星测量它们在表面水域中的丰度(绿色水域含有高浓度的浮游植物，而蓝色水域含有低浓度的浮游植物)。这每隔几天就会为我们提供整个地球上浮游植物数量的信息。浮游植物也会以荧光的形式发出少量的红光。这种荧光包含有关浮游植物群落的生理或健康信息。这也可以用卫星来测量。在我们的节目中，我们将试图进一步了解如何解释和纠正这种荧光发射的测量结果。测量海洋颜色的卫星还提供有关其他吸收和散射(颗粒反射的光)组件的信息，有许多算法和方法可以获得这种测量。然而，在这个遥测信号中似乎有未被利用的信息，这些信息仍有待理解。我们将使用一种新的方法来观察卫星信号中的异常，试图确定这种信号的来源，并探索如何利用它来从太空获得更多关于海洋的信息。 要了解卫星对光的测量，一个非常重要的方面是了解哪些粒子向卫星后向散射光。事实上，虽然我们能够测量光线，但我们还不知道是哪些粒子将阳光散射回卫星传感器。在我们的计划中，我们与4个国际合作者小组合作，启动了一个大型项目来检查粒子的后向散射效率，以便更好地了解这种后向散射的来源。这将使我们能够更好地解释我们正在使用卫星测量的信息，并对海洋的运作有新的见解。

Phytoplankton are photosynthetic microbes that are ubiquitous in natural waters; they are an essential part of aquatic ecosystems as they form the base of many food webs. They include an incredible diversity of shapes, sizes, and species. When ecosystems are altered by human influences, in particular by the addition of nutrients from agricultural runoff, phytoplankton species that were not previously abundant can proliferate. When these species are harmful (producing toxins), such as some bloom-forming cyanobacteria species, the quality of water for drinking or recreation can be compromised. In our research program, we are interested in understanding why some phytoplankton species are present at certain times and under which environmental conditions they are favored. To this end, we have deployed an autonomous research platform that allows us (using a sophisticated "submersible microscope" in a lake) to follow through time the species present as well as their grazers (zooplankton), in addition to other important factors such as nutrients and light. We also aim to understand how changes in the phytoplankton community affect other parts of the ecosystem. In the next few years, we will be focusing on the important role of the abundant aquatic bacteria. Because they are photosynthetic, just like plants on land, some are adapted to high light environments (growing near the surface) and others prefer dim light. Some phytoplankton can easily adjust to fast transitions from dim to high light, but others cannot. In our program, we will study in the laboratory how different species acclimate to these shifts in light levels, in particular how efficiently they can achieve this acclimation at different times of day. Such studies will allow us to create appropriate models to estimate future changes in phytoplankton abundance and productivity. Because phytoplankton absorb light, we can measure their abundance in surface waters using satellites (green waters contain high concentrations of phytoplankton, while blue waters contain low concentrations). This provides us with information about phytoplankton abundances over the whole planet every few days. Phytoplankton also emit a small amount of red light in the form of fluorescence. This fluorescence contains information about the physiology - or health - of phytoplankton communities. This can also be measured using satellites. In our program, we will try to further understand how to interpret and correct measurements of this fluorescence emission. Satellites measuring the color of the ocean also provide information about other absorbing and scattering (light bouncing off of particles) components and many algorithms and methods exist to obtain such measurements. Yet, there appears to be untapped information in this remotely measured signal that remains to be understood. We will be using a novel method to look at anomalies in the satellite signal to try to identify the sources of this signal and explore how it could be used to obtain more information about the ocean from space. To understand satellite measurements of light, one very important aspect is to understand which particles are backscattering light to the satellites. Indeed while we are able to measure the light, we do not yet know which particles are responsible for scattering the sunlight back to the satellite sensors. In our program, in collaboration with 4 groups of international collaborators, we are launching a large project to examine the backscattering efficiencies of particles in order to better understand the sources of this backscattering. This should allow us to better interpret the information we are measuring using satellites and gain new insights into the functioning of the oceans.