Doctoral Dissertation Research: Determining the functional relationship between simultaneous co-limitating light and nutrient conditions on phytoplankton growth

浮游植物是一种单细胞海洋藻类，可以吸收二氧化碳并产生氧气，海洋中浮游植物的生长速度受光和营养物质的可获得性控制。然而，还没有实验室研究产生量化营养物质和光线如何相互作用以控制浮游植物生长所需的数据。一些模型认为光和营养物质独立起作用来控制浮游植物的生长，而另一些模型则认为光和营养物质协同作用。关于光和营养物质如何控制浮游植物生长的这两种不同的假设，可能会对这一过程的速度和浮游植物水华的规模产生截然不同的预测。研究人员将利用一系列实验室实验来确定，假设营养物质和光照对浮游植物生长的影响是独立的还是协同作用的，那么这两种限制资源的作用是否最好。这项实验将有助于改进在全球海洋中实施的海洋生态系统模型，但在北极尤其重要，因为由于人为气候变化，那里的光和营养物质的可获得性都在迅速变化。研究人员将在一系列限制生长的硝酸盐(NO3-)和光照条件下种植北极硅藻。单个培养物将在恒温、恒光和恒定营养条件下保存在恒温器中。将有25个独特的相互作用的N3和限光处理组合，使用5个光和5个N3-条件，以及5个在光饱和但N3耗尽的条件下的额外处理。在培养物适应处理后，研究人员将测量浮游植物生物量和光合作用与辐射(P-E)的关系，浮游植物的生长率将根据介质的稀释率确定。然后将计算每个处理的光和营养限制项。最后，最好地描述共同限制光照和营养条件之间的关系的最佳功能关系将通过比较两个已建立的(最小和乘性)关系与限制条款之间的各种非线性关系来确定。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

The growth rate of phytoplankton, single-celled marine algae that take up carbon dioxide and produce oxygen, is controlled in the ocean by the availability of both light and nutrients. However, no laboratory study has generated the data required to quantify how nutrient and light interact to control phytoplankton growth. Some models assume that light and nutrients act independently to control phytoplankton growth, while others assume that light and nutrients act in concert. These two different assumptions about how light and nutrients control phytoplankton growth can produce vastly different predictions about the speed of this process and the magnitude of phytoplankton blooms. The researchers will use a series of laboratory experiments to determine if the effects of nutrients and light on phytoplankton growth is best modeled assuming that the two limiting resources act independently or in concert. This experiment will help to improve marine ecosystem models implemented throughout the world’s oceans, but will be particularly relevant in the Arctic, where light and nutrient availability are both rapidly changing as a result of anthropogenic climate change.The researchers will grow Arctic diatoms across a range of growth-limiting nitrate (NO3-) and light conditions. Individual cultures will be maintained under constant temperature, light, and nutrient conditions in chemostats. There will be 25 unique interacting NO3- and light-limited treatment combinations conducted using five light and five NO3- conditions, as well as five additional treatments at light-saturated but NO3- deplete conditions. Following acclimation of cultures to the treatments, the researchers will measure phytoplankton biomass and photosynthesis vs. irradiance (P-E) relationships, and phytoplankton growth rates will be determined from the dilution rate of the media. Light and nutrient limitation terms will then be calculated for each treatment. Finally, the best functional relationship that best describes the relationship between co-limiting light and nutrient conditions will be determined by comparing the two established (minimum and multiplicative) relationships to a variety of non-linear relationships between the limitation terms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.