title: The nitrogen costs of photosynthesis in a diatom under current and future pCO2.
abstract: With each cellular generation, oxygenic photoautotrophs must accumulate abundant protein complexes that mediate light capture, photosynthetic electron transport and carbon fixation. In addition to this net synthesis, oxygenic photoautotrophs must counter the light-dependent photoinactivation of Photosystem II (PSII), using metabolically expensive proteolysis, disassembly, resynthesis and re-assembly of protein subunits. We used growth rates, elemental analyses and protein quantitations to estimate the nitrogen (N) metabolism costs to both accumulate the photosynthetic system and to maintain PSII function in the diatom Thalassiosira pseudonana, growing at two pCO2 levels across a range of light levels. The photosynthetic system contains c. 15-25% of total cellular N. Under low growth light, N (re)cycling through PSII repair is only c. 1% of the cellular N assimilation rate. As growth light increases to inhibitory levels, N metabolite cycling through PSII repair increases to c. 14% of the cellular N assimilation rate. Cells growing under the assumed future 750 ppmv pCO2 show higher growth rates under optimal light, coinciding with a lowered N metabolic cost to maintain photosynthesis, but then suffer greater photoinhibition of growth under excess light, coincident with rising costs to maintain photosynthesis. We predict this quantitative trait response to light will vary across taxa.
authors.affiliation: Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, E4L 1G7, Canada; Key Laboratory of Tropical Marine Bio-Resources and Ecology, South China Sea Institute of Oceanology, CAS, Guangzhou, 510301, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Li
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Brown
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Jeans
authors.forename: Natalie A
authors.initials: NA
authors.lastname: Donaher
authors.forename: Avery
authors.initials: A
authors.lastname: McCarthy
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Campbell
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis*; D057231:Climate Change; D017377:Diatoms / Q000378:metabolism*; D004784:Environmental Monitoring; D005544:Forecasting; D009584:Nitrogen / Q000378:metabolism*; D009792:Oceans and Seas; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000502:physiology; D012623:Seawater / Q000737:chemistry*
chemical_list: D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide; D009584:Nitrogen
keywords: Photosystem II (PSII); RUBISCO; Thalassiosira; diatom; growth; nitrogen metabolism; ocean acidification; photosynthesis