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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
Author(s) -
Stefanski Artur,
Bermudez Raimundo,
Sendall Kerrie M.,
Montgomery Rebecca A.,
Reich Peter B.
Publication year - 2020
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.14805
Subject(s) - ecotone , environmental science , boreal , context (archaeology) , global warming , atmospheric sciences , temperate climate , taiga , biome , climate change , ecology , biology , ecosystem , habitat , paleontology , geology
Photosynthetic biochemical limitation parameters (i.e., V cmax , J max and J max : V cmax 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 ( V cmax25°C and J max25°C , respectively) were estimated based on A C i curves measured in situ over three growing seasons. Our primary objective was to test whether species would downregulate V cmax25°C and J max25°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 V cmax25°C or J max25°C ( p > .14). However, J max : V cmax ratio decreased significantly with warming ( p = .0178), whereas interactions between warming and rainfall reduction on the J max25°C to V cmax25°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 J max25°C and V cmax25°C when grown at elevated temperatures, reduced rainfall, or both combined.