Friday, August 6, 2010 - 8:20 AMCOS 107-2: Linking community and ecosystem dynamics through measurements of elemental composition of single plankton cells
Stephen B. Baines, Stony Brook University
Background/Question/Methods
Biogeochemical cycles of elements are often linked through the elemental content of organisms involved in the transport and transformation of material. Recently it has become increasingly clear that the elemental composition of organisms can vary substantially among or within communities. Such variation reflects physiological responses to the environment and differences among species. Far from being random, such interspecific variations in elemental composition are often linked to ecologically important traits, such as growth rate, ability to perform certain metabolic tasks, or susceptibility to predation. To the extent that organisms with certain traits are favored by a certain environment or a specific set of biological interactions, the elemental composition of organisms should vary correspondingly. The plankton represents a particularly useful system to investigate such linkages between community processes and biogeochemical cycles because of the speed of the community response and the diversity of organisms comprising planktonic communities. Moreover, recent methodological advances allow us to assess elemental composition of single cells directly, and even to map elemental content on a subcellular level.
We address three questions: 1) Do diatom communities in the ocean vary in their elemental content among regions of the ocean? 2) Can we develop a model that predicts elemental content of diatoms based on biological interactions and responses to the environment, 2) Can this model explain interregional differences in plankton elemental content among regions of the ocean. To address these questions, we employ synchrotron based x-ray fluorescence microscopy (SXRF) to estimate elemental content of single diatom cells within the plankton. We then show that cells with specific elemental composition can be favored if the elemental content of diatoms is a proxies for ecological performance
Results/Conclusions
We found large interregional and interspecific Si, P and Fe content between diatoms collected from the tropical ocean and ocean water communities at higher latitude. These differences are correlated to major biogeochemical differences between the regions. Experiments show that they cannot be explained by physiological responses alone. Instead, differences in community structure seem to play a major role. We developed a model based on equilibrium resource ratio theory in which the elemental content is correlated with zero net growth isoclines or predation resistance. This model suggests that several possible strategies can be employed by diatoms to facilitate coexistence and that all of these have strong impacts on elemental content of diatom species, and thus biogeochemical cycles. It also suggests that low temperatures place a priority on preventing loss to predation.
Biogeochemical cycles of elements are often linked through the elemental content of organisms involved in the transport and transformation of material. Recently it has become increasingly clear that the elemental composition of organisms can vary substantially among or within communities. Such variation reflects physiological responses to the environment and differences among species. Far from being random, such interspecific variations in elemental composition are often linked to ecologically important traits, such as growth rate, ability to perform certain metabolic tasks, or susceptibility to predation. To the extent that organisms with certain traits are favored by a certain environment or a specific set of biological interactions, the elemental composition of organisms should vary correspondingly. The plankton represents a particularly useful system to investigate such linkages between community processes and biogeochemical cycles because of the speed of the community response and the diversity of organisms comprising planktonic communities. Moreover, recent methodological advances allow us to assess elemental composition of single cells directly, and even to map elemental content on a subcellular level.
We address three questions: 1) Do diatom communities in the ocean vary in their elemental content among regions of the ocean? 2) Can we develop a model that predicts elemental content of diatoms based on biological interactions and responses to the environment, 2) Can this model explain interregional differences in plankton elemental content among regions of the ocean. To address these questions, we employ synchrotron based x-ray fluorescence microscopy (SXRF) to estimate elemental content of single diatom cells within the plankton. We then show that cells with specific elemental composition can be favored if the elemental content of diatoms is a proxies for ecological performance
Results/Conclusions
We found large interregional and interspecific Si, P and Fe content between diatoms collected from the tropical ocean and ocean water communities at higher latitude. These differences are correlated to major biogeochemical differences between the regions. Experiments show that they cannot be explained by physiological responses alone. Instead, differences in community structure seem to play a major role. We developed a model based on equilibrium resource ratio theory in which the elemental content is correlated with zero net growth isoclines or predation resistance. This model suggests that several possible strategies can be employed by diatoms to facilitate coexistence and that all of these have strong impacts on elemental content of diatom species, and thus biogeochemical cycles. It also suggests that low temperatures place a priority on preventing loss to predation.