Allison Steven D.
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PreprintResource allocation by the marine cyanobacterium Synechococcus WH8102 in response to different nutrient supply ratios( 2015-05) Mouginot, Céline ; Zimmerman, Amy E. ; Bonachela, Juan A. ; Fredricks, Helen F. ; Allison, Steven D. ; Van Mooy, Benjamin A. S. ; Martiny, Adam C.Differences in relative availability of nitrate vs. phosphate may contribute to regional variations in plankton elemental stoichiometry. As a representative of the globally abundant marine Synechococcus, strain WH8102 was grown in 16 chemostats up to 52 days at a fixed growth rate with nitrogen-phosphorus ratios (N:Psupply) of 1 to 50. Initially, the phosphate and nitrate concentrations in the vessel decreased when the respective nutrient was limiting. Cell growth generally stabilized, although several chemostats had apparent oscillations in biomass. We observed extensive plasticity in the elemental content and ratios. N:Pcell matched the supply values between N:Psupply 5 and 20. The C:Pcell followed a similar trend. In contrast, the mean C:Ncell was 6.8 and did not vary as a function of supply ratios. We also observed that induction of alkaline phosphatase, the fraction of P allocated to nucleic acids, and the lipid sulfoquinovosyldiacylglycerol:phosphatidyglycerol ratio inversely correlated with P availability. Our results suggest that this extensive plasticity in the elemental content and ratios depends both on the external nutrient availability as well as past growth history. Thus, our study provides a quantitative understanding of the regulation of the elemental stoichiometry of an abundant ocean phytoplankton lineage.
PreprintDecreased mass specific respiration under experimental warming is robust to the microbial biomass method employed( 2009-05) Bradford, Mark A. ; Wallenstein, Matthew D. ; Allison, Steven D. ; Treseder, Kathleen K. ; Frey, Serita D. ; Watts, Brian W. ; Davies, Christian A. ; Maddox, Thomas R. ; Melillo, Jerry M. ; Mohan, Jacqueline E. ; Reynolds, James F.Hartley et al. question whether reduction in Rmass, under experimental warming, arises because of the biomass method. We show the method they treat as independent yields the same result. We describe why the substrate-depletion hypothesis cannot alone explain observed responses, and urge caution in the interpretation of the seasonal data.