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1. Global patterns and predictors of C:N:P in marine ecosystems

   https://doi.org/10.1038/s43247-022-00603-6  

   Tanioka, Tatsuro; Garcia, Catherine A.; Larkin, Alyse A.; Garcia, Nathan S.; Fagan, Adam J.; Martiny, Adam C. (December 2022, Communications Earth & Environment)

   Abstract Oceanic nutrient cycles are coupled, yet carbon-nitrogen-phosphorus (C:N:P) stoichiometry in marine ecosystems is variable through space and time, with no clear consensus on the controls on variability. Here, we analyze hydrographic, plankton genomic diversity, and particulate organic matter data from 1970 stations sampled during a global ocean observation program (Bio-GO-SHIP) to investigate the biogeography of surface ocean particulate organic matter stoichiometry. We find latitudinal variability in C:N:P stoichiometry, with surface temperature and macronutrient availability as strong predictors of stoichiometry at high latitudes. Genomic observations indicated community nutrient stress and suggested that nutrient supply rate and nitrogen-versus-phosphorus stress are predictive of hemispheric and regional variations in stoichiometry. Our data-derived statistical model suggests that C:P and N:P ratios will increase at high latitudes in the future, however, changes at low latitudes are uncertain. Our findings suggest systematic regulation of elemental stoichiometry among ocean ecosystems, but that future changes remain highly uncertain. 

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2. Variable Stoichiometry Effects on Glacial/Interglacial Ocean Model Biogeochemical Cycles and Carbon Storage

   Fillman, Nathaniel (June 2023, Scholar's Archive at OSU)

   Realistic model representation of ocean phytoplankton is important for simulating nutrient cycles and the biological carbon pump, which affects atmospheric carbon dioxide (pCO2) concentrations and, thus, climate. Until recently, most models assumed constant ratios (or stoichiometry) of phosphorous (P), nitrogen (N), silicon (Si), and carbon (C) in phytoplankton, despite observations indicating systematic variations. Here, we investigate the effects of variable stoichiometry on simulated nutrient distributions, plankton community compositions, and the C cycle in the preindustrial (PI) and glacial oceans. Using a biogeochemical model, a linearly increasing P:N relation to increasing PO4 is implemented for ordinary phytoplankton (PO), and a nonlinearly decreasing Si:N relation to increasing Fe is applied to diatoms (PDiat). C:N remains fixed. Variable P:N affects modeled community composition through enhanced PO4 availability, which increases N-fixers in the oligotrophic ocean, consistent with previous research. This increases the NO3 fertilization of PO, the NO3 inventory, and the total plankton biomass. The accuracy of modeled surface nutrients is relatively unchanged. Conversely, variable Si:N shifts south the Southern Ocean’s meridional surface silicate gradient, which aligns better with observations, but depresses PDiat growth globally. In Last Glacial Maximum simulations, PO respond to more oligotrophic conditions by increasing their C:P. This strengthens the biologically mediated C storage such that dissolved organic (inorganic) C inventories increase by 34-40 (38-50) Pg C and 0.7-1.2 Pg yr-1 more particulate C is exported into the interior ocean. Thus, an additional 13-14 ppm of pCO2 difference from PI levels results, improving model agreement with glacial observations. 

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3. N and P constrain C in ecosystems under climate change: Role of nutrient redistribution, accumulation, and stoichiometry

   https://doi.org/10.1002/eap.2684  

   Rastetter, Edward B.; Kwiatkowski, Bonnie L.; Kicklighter, David W.; Barker Plotkin, Audrey; Genet, Helene; Nippert, Jesse B.; O'Keefe, Kimberly; Perakis, Steven S.; Porder, Stephen; Roley, Sarah S.; et al (July 2022, Ecological Applications)

   We use the Multiple Element Limitation (MEL) model to examine the responses of twelve ecosystems - from the arctic to the tropics and from grasslands to forests - to elevated carbon dioxide (CO2), warming, and 20% decreases or increases in annual precipitation. The ecosystems respond synergistically to elevated CO2, warming, and decreased precipitation combined because higher water use efficiency with elevated CO2 and higher fertility with warming compensate for the responses to drought. The response to elevated CO2, warming, and increased precipitation combined is additive. We analyze changes in ecosystem carbon (C) sequestration based on four nitrogen (N) and four phosphorus (P) attribution factors of the ecosystem: (1) changes in total N and P in the ecosystem, (2) changes in the distribution of N and P between vegetation and soil, (3) changes in vegetation C:N and C:P ratios, and (4) changes in soil C:N and C:P ratios. In the combined CO2 and climate change simulations, all ecosystems gain C. The relative contribution of changes in these four N and P attribution factors to changes in ecosystem C storage varies among ecosystems because of differences in the initial distributions of N and P between vegetation and soil and the openness of the ecosystem N and P cycles. The net transfer of N and P from soil (low C:N and C:P) to vegetation (high C:N and C:P) dominates the C response of forests. For tundra and grassland ecosystems, the C gain is also associated with an increase in soil C:N and C:P. In ecosystems with symbiotic N fixation, gains in C resulted from the accumulation of N and sometimes P. Because of differences in the openness of the N versus P cycles and the distribution of organic matter between vegetation and soil, changes in the N attribution factors do not always parallel changes in the P attribution factors. These findings highlight how differences among ecosystems in C-nutrient interactions and the amount of woody biomass interact to shape ecosystem C sequestration under simulated global change. By using a single model framework across multiple ecosystems, we suggest that a better understanding of the factors influencing the openness of the N and P cycles, controls on N and P distribution within ecosystems, and controls on ecosystem stoichiometry is needed to improve the representation of nutrient effects on C sequestration in ecosystems and their responses to elevated CO2 and climate change. 

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4. Temperature and interspecific interactions drive differences in carbon use efficiencies and biomass stoichiometry among aquatic fungi

   https://doi.org/10.1093/femsec/fiad021  

   Tomczyk, Nathan J; Rosemond, Amy D; Whiteis, Ally M; Benstead, Jonathan P; Gulis, Vladislav (February 2023, FEMS Microbiology Ecology)

   Abstract Saprotrophic fungi play important roles in transformations of carbon (C), nitrogen (N), and phosphorus (P) in aquatic environments. However, it is unclear how warming will alter fungal cycling of C, N, and P. We conducted an experiment with four aquatic hyphomycetes (Articulospora tetracladia, Hydrocina chaetocladia, Flagellospora sp., and Aquanectria penicillioides), and an assemblage of the same taxa, to test how temperature alters C and nutrient use. Specifically, we evaluated biomass accrual, C:N, C:P, δ13C, and C use efficiency (CUE) over a 35-d experiment with temperatures ranging from 4ºC to 20ºC. Changes in biomass accrual and CUE were predominantly quadratic with peaks between 7ºC and 15ºC. The C:P of H. chaetocladia biomass increased 9× over the temperature gradient, though the C:P of other taxa was unaffected by temperature. Changes in C:N were relatively small across temperatures. Biomass δ13C of some taxa changed across temperatures, indicating differences in C isotope fractionation. Additionally, the 4-species assemblage differed from null expectations based on the monocultures in terms of biomass accrual, C:P, δ13C, and CUE, suggesting that interactions among taxa altered C and nutrient use. These results highlight that temperature and interspecific interactions among fungi can alter traits affecting C and nutrient cycling. 

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5. Varying influence of phytoplankton biodiversity and stoichiometric plasticity on bulk particulate stoichiometry across ocean basins

   https://doi.org/10.1038/s43247-021-00212-9  

   Lomas, Michael W.; Baer, Steven E.; Mouginot, Celine; Terpis, Kristina X.; Lomas, Debra A.; Altabet, Mark A.; Martiny, Adam C. (December 2021, Communications Earth & Environment)

   null (Ed.)

   Abstract Concentrations and elemental ratios of suspended particulate organic matter influence many biogeochemical processes in the ocean, including patterns of phytoplankton nutrient limitation and links between carbon, nitrogen and phosphorus cycles. Here we present direct measurements of cellular nutrient content and stoichiometric ratios for discrete phytoplankton populations spanning broad environmental conditions across several ocean basins. Median cellular carbon-to-phosphorus and nitrogen-to-phosphorus ratios were positively correlated with vertical nitrate-to-phosphate flux for all phytoplankton groups and were consistently higher for cyanobacteria than eukaryotes. Light and temperature were inconsistent predictors of stoichiometric ratios. Across nutrient-rich and phosphorus-stressed biomes in the North Atlantic, but not in the nitrogen-stressed tropical North Pacific, we find that a combination of taxonomic composition and environmental acclimation best predict bulk particulate organic matter composition. Our findings demonstrate the central role of plankton biodiversity and plasticity in controlling linkages between ocean nutrient and carbon cycles in some regions. 

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