Role of Growth Rate and Grazing Mortality in Regulating the Dynamics of Photosynthetic Prokaryotic Picoplankton in the Sargasso Sea

生长率和放牧死亡率在调节马尾藻海光合原核超微型浮游生物动态中的作用

• 批准号: 9911534
• 负责人: Brian Binder
• 金额: $ 32.6万
• 依托单位: University of Georgia Research Foundation Inc
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-06-01 至 2004-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9911534&HistoricalAwards=false
• 关键词: Role; Growth; Rate; Grazing; Mortality

Two closely related unicellular cyanobacteria, Prochlorococcus and Synechococcus, are responsible for a significant fraction of total oceanic primary production. Although these two picoplankton groups are ubiquitous and abundant in most parts of the ocean, their distribution in time and space is often contrasting. This pattern is particularly evident over the course of the seasonal cycle in the NW Sargasso Sea, where Prochlorococcus dominates during the summer (under highly stratified, low nutrient conditions), and Synechococcus typically dominates during the winter (under well-mixed conditions). The fact that the summed biomass of these two groups remains approximately constant has led to the suggestion that together these organisms fill some sort of "picophytoplankton niche" in this environment. Explanations for these contrasting patterns of Prochlorococcus and Synechococcus distribution are most often framed in the context of growth rate regulation: dominance by one or the other group is assumed to reflect faster growth by that group under the environmental conditions prevailing at the time. However, the abundance of a natural population must reflect the relative balance between both growth and mortality terms, and there is no firm theoretical requirement that growth rate and standing stock be correlated. In fact, the few studies to date that have simultaneously examined the growth rates of both Prochlorococcus and Synechococcus in the field have found no such correlation. These results suggest that factors other than differential growth rate limitation are important in regulating the relative abundance of these two picophytoplankton groups in oceanic environments.This project seeks to examine the relationship between growth rate, grazing mortality, and relative abundance of Prochlorococcus and Synechococcus, over the course of the well-defined seasonal cycle in the abundance of these two groups in the Sargasso Sea. A suite of overlapping and complementary approaches for measuring these processes in natural picoplankton populations will be applied during four research cruises. Specifically, the following questions will be addressed: Are seasonal changes in the relative abundance of Prochlorococcus and Synechococcus correlated with changes in the relative growth and grazing mortality rates of these populations? Are there significant seasonal changes in micro-grazer abundance or activity? Do such changes influence the seasonal cycle of picophytoplankton standing stock? Are there detectable differences in the functional response of the protozoan community to Prochlorococcus and Synechococcus abundance? Do these differences influence the seasonal cycle of picophytoplankton? Do cell cycle-based estimates of in situ growth rate coincide with estimates from dilution experiments? Are estimates of grazing mortality based on fluoresecently-labeled prey consistent with estimates from these experiments?Unraveling the mechanisms by which the relative dominance of these two picophytoplankton groups (and their summed biomass) is regulated would lead to a better understanding of the more general, but much less tractable, issue of regulation of overall phytoplankton community structure.

两种密切相关的单细胞蓝细菌，原绿球藻和聚球藻，负责总海洋初级生产的一个重要部分。虽然这两种微型浮游生物在海洋的大部分地区都是普遍存在和丰富的，但它们在时间和空间上的分布往往是截然不同的。这种模式在西北马尾藻海的季节循环过程中特别明显，在夏季（在高度分层，低营养条件下），原绿球藻占主导地位，而聚球藻通常在冬季（在混合良好的条件下）占主导地位。这两个群体的总生物量保持大致恒定的事实导致了这样的建议，即这些生物共同填补了这种环境中的某种“微型浮游植物生态位”。这些对比模式的原绿球藻和聚球藻分布的解释，最经常在生长速率调节的上下文中框定：由一个或另一个组的优势被认为是反映更快的增长，该组在当时的环境条件下占主导地位。然而，自然种群的丰富度必须反映出增长率和死亡率之间的相对平衡，并且没有严格的理论要求增长率和现存量相互关联。事实上，到目前为止，少数同时研究原绿球藻和聚球藻生长速率的研究没有发现这种相关性。这些结果表明，差异增长率限制以外的因素是重要的，在调节这两个picophytoplankton组在海洋environments.This项目的相对丰度的增长率，放牧死亡率，和相对丰度的原绿球藻和聚球藻之间的关系，在明确的季节性周期的过程中，这两个群体在马尾藻海的丰度。一套重叠和互补的方法来测量自然微型浮游生物种群的这些过程将在四个研究巡航应用。具体而言，以下问题将得到解决：季节性变化的相对丰富的原绿球藻和聚球藻相关的相对增长和放牧死亡率的变化，这些人口？微型食草动物的丰度或活动是否有显著的季节性变化？这些变化是否影响了微型浮游植物现存量的季节性循环？原生动物群落对原绿球藻和聚球藻丰度的功能反应是否存在可检测的差异？这些差异会影响微微型浮游植物的季节性循环吗？基于细胞周期的原位生长速率估计值与稀释实验的估计值是否一致？基于荧光标记猎物的放牧死亡率的估计与这些实验的估计一致吗？解开机制，这两个picophytoplankton组（和他们的总生物量）的相对优势进行调节，将导致更好地了解更普遍的，但更不容易处理，整个浮游植物群落结构的调节问题。