The control of photosynthetic quantum yield of phytoplankton by light intensity and diapycnal nutrient flux

海洋初级生产力可能是海洋碳循环中最鲜为人知的部分。初级生产力鲜为人知的一个原因是缺乏对浮游植物生理学中地理和时间变异性的了解。例如，直到最近，所谓的光保护色素的重要性才被揭示出来，这种色素实际上可以保护光合作用装置免受太多阳光的伤害。这个项目将研究海洋光合作用的一项基本性质的地理和时间变异性：量子产量，即可用光与光合作用中固定的碳量的比率。PI根据以前的测量提出了一个假设，即在分层海洋的真光区的下部，营养物质向上的通量调节量子产率的值，而在上层，光照度通过浮游植物的色素组成来控制量子产生值。这一假设将通过非常仔细和全面地测量浮游植物的生物光学特性和物种组成以及海底光环境、水文和营养物质来估计量子产率的最大值来验证。这些测量将沿着海洋中的时间和空间梯度进行，为量子产率的环境调节奠定基础。这些测量将被用来精确地确定量子产率的最大值是如何受到太阳通量和植物营养的调节的。这项研究为理解营养供应和光照过程如何影响浮游植物自然种群的生理提供了一种机制，浮游植物是生物海洋学中一个长期存在的问题。它还提供了一种改进建模基本生产力的方法，包括从空间估计全球海洋的生产力。这项研究将有助于更好地了解浮游植物在全球碳循环中的作用，以及气候变化对海洋初级生产力的影响。该项目提供一名博士后和一名或多名研究生的培训，结果将在具有教育功能的公共网站上传播。

Primary production in the ocean is probably the least known part of the ocean's carbon cycle. One reason that primary production is little known is the lack of understanding of the geographical and temporal variability in phytoplankton physiology. For example it is only recently that the importance has been revealed, of the so-called photoprotectant pigments, pigments that, in effect, shield the photosynthetic apparatus from too much sunlight. This project will investigate the geographic and temporal variability of a fundamental property of oceanic photosynthesis: the quantum yield, or the ratio of the available light to the amount of carbon fixed in photosynthesis. The PIs propose an hypothesis based on earlier measurements, that in the lower parts of the euphotic zone in the stratified ocean, the upward flux of nutrients regulates the value of the quantum yield, while in the upper parts, irradiance governs its value, through the pigment composition of the phytoplankton. This hypothesis will be tested by making estimates of the quantum yield's maximum value through very careful and comprehensive measurements of the bio-optical properties and species composition of the phytoplankton, as well as the submarine light environment, hydrography, and nutrients. These measurements will be along both temporal and spatial gradients in the ocean to create the basis for environmental regulation of quantum yield. These measurements will be used to establish precisely how the maximum value of the quantum yield is regulated by solar flux and plant nutrients. This research provides a mechanism to understand how the processes of nutrient supply and light affect the physiology of natural populations of phytoplankton, a long-standing problem in biological oceanography. It also provides a means for improving the modeling primary productivity, including estimating productivity in the global ocean from space. The research will aid in developing a better understanding of the role of phytoplankton in the global carbon cycle, and also the affects of climate change on primary production in the ocean. The project provides for the training of a post-doc and one or more graduate students, and results will be disseminated public web sites that serve an educational function.