title: Effects of CO2 on the tolerance of photosynthesis to heat stress can be affected by photosynthetic pathway and nitrogen.
abstract: OBJECTIVE
  Determining effects of elevated CO2 and N on photosynthetic thermotolerance is critical for predicting plant responses to global warming.
  
  
  METHODS
  We grew Hordeum vulgare (barley, C3) and Zea mays (corn, C4) at current or elevated CO2 (370, 700 ppm) and limiting or optimal soil N (0.5, 7.5 mmol/L). We assessed thermotolerance of net photosynthesis (Pn), photosystem II efficiency in the light (Fv'/Fm'), photochemical quenching (qp), carboxylation efficiency (CE), and content of rubisco activase and major heat-shock proteins (HSPs).
  
  
  RESULTS
  For barley, elevated CO2 had no effect on Pn, qp, and CE at both high and low N and only a positive effect on Fv'/Fm' at high N. However, for corn, Pn, Fv'/Fm', qp, and CE were decreased substantially by elevated CO2 under high and low N, with greater decreases at high N for all but qp. The negative effects of high CO2 during heat stress on photosynthesis were correlated with rubisco activase and HSPs content, which decreased with heat stress, especially for low-N corn.
  
  
  CONCLUSIONS
  These results indicate that stimulatory effects of elevated CO2 at normal temperatures on photosynthesis and growth (only found for high-N barley) may be partly offset by neutral or negative effects during heat stress, especially for C4 species. Thus, CO2 and N effects on photosynthetic thermotolerance may contribute to changes in plant productivity, distribution, and diversity in future.
authors.affiliation: International Center for Ecology, Meteorology and Environment, School of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing 210044, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Wang
authors.forename: Scott A
authors.initials: SA
authors.lastname: Heckathorn
authors.forename: E William
authors.initials: EW
authors.lastname: Hamilton
authors.forename: Jonathan
authors.initials: J
authors.lastname: Frantz
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects* / Q000528:radiation effects; D000704:Analysis of Variance; D018533:Biomass; D002245:Carbon Dioxide / Q000494:pharmacology*; D006360:Heat-Shock Proteins / Q000378:metabolism; D018869:Heat-Shock Response / Q000187:drug effects* / Q000528:radiation effects; D001467:Hordeum / Q000187:drug effects / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D006358:Hot Temperature; D008027:Light; D009584:Nitrogen / Q000494:pharmacology*; D010788:Photosynthesis / Q000187:drug effects* / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology; D003313:Zea mays / Q000187:drug effects / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects
chemical_list: D006360:Heat-Shock Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C054765:rca protein, plant; D002245:Carbon Dioxide; D009584:Nitrogen
keywords: climate change; heat shock proteins; thermotolerance