Surprising lack of sensitivity of biochemical limitation of photosynthesis of nine tree species to open-air experimental warming and reduced rainfall in a southern boreal forest

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Abstract

Photosynthetic biochemical limitation parameters (i.e., Vcmax, Jmax and Jmax:Vcmax ratio) are sensitive to temperature and water availability, but whether these parameters in cold climate species at biome ecotones are positively or negatively influenced by projected changes in global temperature and water availability remains uncertain. Prior exploration of this question has largely involved greenhouse based short-term manipulative studies with mixed results in terms of direction and magnitude of responses. To address this question in a more realistic context, we examined the effects of increased temperature and rainfall reduction on the biochemical limitations of photosynthesis using a long-term chamber-less manipulative experiment located in northern Minnesota, USA. Nine tree species from the boreal-temperate ecotone were grown in natural neighborhoods under ambient and elevated (+3.4°C) growing season temperatures and ambient or reduced (≈40% of rainfall removed) summer rainfall. Apparent rubisco carboxylation and RuBP regeneration standardized to 25°C (Vcmax25°C and Jmax25°C, respectively) were estimated based on ACi curves measured in situ over three growing seasons. Our primary objective was to test whether species would downregulate Vcmax25°C and Jmax25°C in response to warming and reduced rainfall, with such responses expected to be greatest in species with the coldest and most humid native ranges, respectively. These hypotheses were not supported, as there were no overall main treatment effects on Vcmax25°C or Jmax25°C (p >.14). However, Jmax:Vcmax ratio decreased significantly with warming (p =.0178), whereas interactions between warming and rainfall reduction on the Jmax25°C to Vcmax25°C ratio were not significant. The insensitivity of photosynthetic parameters to warming contrasts with many prior studies done under larger temperature differentials and often fixed daytime temperatures. In sum, plants growing in relatively realistic conditions under naturally varying temperatures and soil moisture levels were remarkably insensitive in terms of their Jmax25°C and Vcmax25°C when grown at elevated temperatures, reduced rainfall, or both combined.

Original languageEnglish (US)
Pages (from-to)746-759
Number of pages14
JournalGlobal change biology
Volume26
Issue number2
DOIs
StatePublished - Feb 1 2020

Bibliographical note

Funding Information:
We would like to thank to Danielle A. Way for stimulating discussion and helpful commentary also we would like to thank to Paul V. Bolstad and Ethan E. Butler for helpful comments and suggestions. This research was supported by the U.S Department of Energy, Office of Science, and Office of Biological and Environmental Research award number DE-FG02-07ER64456; Minnesota Agricultural Experiment Station MN-42-030 and MN-42-060; the Minnesota Department of Natural Resources; College of Food, Agricultural, and Natural Resources Sciences and Wilderness Research Foundation, University of Minnesota. Assistance with experimental operation and data collections was provided by Karen Rice-David, Michelle Cummings and numerous summer interns.

Publisher Copyright:
© 2019 John Wiley & Sons Ltd

Keywords

  • B4WarmED
  • J
  • V
  • biochemical limitation
  • boreal forest
  • experimental warming
  • rainfall reduction

PubMed: MeSH publication types

  • Journal Article

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