Role of variable picoplankton cellular phosphorus turnover and allocation in marine phosphorus cycling

磷是生命的关键元素，在广阔的海洋中心区域通常含量较低，有时达到生物生产力的极限浓度。微生物对溶解磷的吸收是控制微生物生产以及海洋磷的归宿和循环的重要杠杆。该项目将研究以下假设：在贫营养环境中，微生物细胞磷的周转速度比细胞生物量周转速度更快，导致磷大量返回溶解池。磷的快速返回可以重新供应生物可利用的磷库，影响微生物动态并促进表层海洋中磷的大量循环利用。 特别是，这项研究将使用现场样本来确定居住在马尾藻海（百慕大附近的北大西洋中部地区）磷耗尽的地表水中的极小藻类和细菌的主要群体的细胞磷和生物量周转率。 该项目将由两名职业生涯早期的女科学家共同领导。 他们的教育工作将包括培训本科生助理以及对 K-12 学生的公共教育推广。生物地球化学循环研究的主要目标是将化学通量与生物体活动联系起来。这项工作将通过将海洋表层的磷通量与特定微生物群的活动联系起来，并为控制这些通量的因素提供一个机制框架，为理解磷的生物地球化学循环做出基础贡献。这项研究的一个重要的新颖产品将是确定公海中单个超微型浮游生物群的细胞磷周转率相对于生物量周转率。 为了建立对控制这些速率的过程的机械理解，该项目还将确定超微型浮游生物将磷分配到细胞内生化物质中的变化。 现场测量将通过对代表马尾藻海细胞分选群体的无菌培养物实验进行增强，以进行更详细的生化分析。研究小组将利用一套独特的工具对环境样本进行新颖的测量：流式细胞术和荧光激活细胞分选将与放射性同位素标记和生化分析相结合，以量化细胞特异性磷通量并表征这些通量的化学形态。 细胞磷周转率与生物量周转率的高比例具有双重意义：（1）微生物生物质中的磷含量会低估支持微生物生长所需的总磷需求，（2）通过微生物的吸收和快速返回溶解池，溶解磷可能在表层海洋中发生显着的循环。通过测量现场样本中的这些速率，研究小组希望回答有关不同微生物群对海洋表面磷通量的相对影响以及驱动这些通量的细胞动力学的关键问题。

Phosphorus is a key element for life, often present in low amounts in the vast central regions of the ocean and sometimes reaching limiting concentrations for biological productivity. Microbial uptake of dissolved phosphorus is an important lever in controlling both microbial production and the fate and cycling of marine phosphorus. This project will investigate the hypothesis that in oligotrophic environments, microbial cellular turnover of phosphorus occurs more rapidly than cellular biomass turnover, leading to a significant return of phosphorus to the dissolved pool. This rapid return of phosphorus could resupply the pool of bioavailable phosphorus, impacting microbial dynamics and fueling significant recycling of phosphorus in the surface ocean. In particular, this research will use field samples to determine the rates of cellular phosphorus and biomass turnover in the dominant groups of very small algae and bacteria inhabiting the phosphorus-depleted, surface waters of the Sargasso Sea (the region of the central North Atlantic Ocean near Bermuda). The project will be co-directed by two early-career women scientists. Their educational efforts will include training of an undergraduate student assistant as well as public educational outreach to K-12 students.A primary objective in the study of biogeochemical cycles is linking chemical fluxes to the activity of organisms. This work will make fundamental contributions to the understanding of the biogeochemical cycling of phosphorus by linking phosphorus fluxes in the surface ocean to the activity of specific groups of microbes, and providing a mechanistic framework for the factors that control these fluxes. A significant, novel product of this research will be the determination of cellular phosphorus turnover rates relative to biomass turnover rates for individual picoplankton groups in the open ocean. To build a mechanistic understanding of the processes controlling these rates, this project will also determine the variation in picoplankton allocation of phosphorus into intracellular biochemicals. Field measurements will be augmented with experiments on axenic cultures, representative of the cell-sorted groups from the Sargasso Sea, to conduct more detailed biochemical analyses. The research team will utilize a unique suite of tools to make novel measurements from environmental samples: flow cytometry and fluorescence activated cell sorting will be combined with radioisotope labeling and biochemical analyses to quantify cell-specific phosphorus fluxes and characterize the chemical speciation of these fluxes. The significance of a high ratio of cellular phosphorus turnover rate to biomass turnover rate would be two-fold: (1) the amount of phosphorus in microbial biomass would underestimate the total phosphorus demand necessary to support microbial growth, and (2) significant recycling of dissolved phosphorus may occur in the surface ocean through microbial uptake and rapid return to the dissolved pool. By measuring these rates in field samples, the team expects to answer crucial questions about the relative impact of different microbial groups on surface ocean phosphorus fluxes and the cellular dynamics that drive these fluxes.