All organisms are made up of the same set of chemical elements such as carbon (C), nitrogen (N), and phosphorus (P), although there are differences in the proportions of these elements among species. Such diversity affects the roles organisms play in key ecosystem services such as carbon sequestration and nutrient cycling. However, scientists don't yet have a complete understanding of the biological rules that dictate the proportions of C, N, and P in living things. One hypothesis is that C:N:P proportions are a function of how fast an organism grows because, to grow fast, organisms must produce P-rich structures to drive rapid construction of cellular materials. While various data support this view, other studies do not and so researchers do not yet know when this "growth rate rule" holds and when it doesn't. This project will subject three species (a bacterium, an alga, and a crustacean) to a variety of environmental and evolutionary conditions to see when C:N:P proportions of each organism follow this "growth rate rule" and when they don't. The research team will also build mathematical models of these processes to predict what happens when organisms that do (or do not) follow the growth rate rule interact with each other. The proposed research will advance scientific understanding how food webs and ecosystems work and improve predictions of how they respond to perturbations, including increasing atmospheric carbon dioxide concentrations and inputs of nitrogen and phosphorus pollution from agriculture and sewage. Furthermore, to help develop a broadly trained scientific work force, the project will partner with local tribal communities to engage Native American undergraduate students in the research.
This project seeks to establish the conditions under which there is or is not a close coupling among growth rate, C:N:P ratios, and cellular allocation to P-rich ribosomes in three taxa: Pseudomonas putida (a heterotrophic bacterium), Chlamydomonas reinhardtii (a photosynthetic alga), and Daphnia pulicaria (a crustacean consumer). First, Pseudomonas, Chlamydomonas, and Daphnia will be grown under limitation by key non-substitutable resources (energy, N, P). Associations among growth, biomass, excretion and remineralization C:N:P stoichiometry, cellular RNA and protein contents, and metabolic rates will be quantified. These measurements will be used to develop mathematical models of these cellular processes. Next, the project will complete a series of evolution experiments, subjecting Pseudomonas, Chlamydomonas, and Daphnia to selection under limitation by different resources. The resulting descendants will be assessed as in the first component of the project. Then, the descendants will be used in ecological experiments to evaluate how evolutionary responses affect ecological processes. Finally, results from these experiments will be used to develop and test new mathematical models of ecological and evolutionary dynamics. The proposed work will produce several resources for use by the scientific community, including data on physiological and transcriptomic responses of three model organisms to ecological challenges as well as a repository of selected lines that will be shared with colleagues. The project will produce uniquely trained postdoctoral researchers, graduate students, and undergraduates with expertise in many disciplines, including genomics, physiology, ecology, evolution, and mathematics. If successful, the project will advance our understanding of biological systems from genes to ecosystems.
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.
