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ARS Home » Midwest Area » Urbana, Illinois » Global Change and Photosynthesis Research » Research » Publications at this Location » Publication #352392
Title: Similar photosynthetic response to elevated carbon dioxide concentration in species with different phloem loading strategies

Author
item BISHOP, KRISTEN - University Of Illinois
item LOMONNIER, PAULINE - Orise Fellow
item QUEBEDEAUX, JENNIFER - University Of Illinois
item MONTES, CHRISTOPHER - University Of Illinois
item LEAKEY, ANDREW D B - University Of Illinois
item Ainsworth, Elizabeth - Lisa

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2018
Publication Date: 6/2/2018
Citation: Bishop, K.A., Lomonnier, P., Quebedeaux, J.C., Montes, C.M., Leakey, A.D.B., Ainsworth, E.A. 2018. Similar photosynthetic response to elevated carbon dioxide concentration in species with different phloem loading strategies. Photosynthesis Research. https://doi.org/10.1007/s11120-018-0524-x.
DOI: https://doi.org/10.1007/s11120-018-0524-x

Interpretive Summary: Species have different mechanisms for loading sugars into phloem, which is the tissue that transports sugars from leaves to roots, flowers and other non-photosynthetic tissues. Some species use sucrose transporter proteins to load sucrose into the phloem whereas other species have symplastic continuity between tissues and sucrose moves passively to the phloem. We tested 5 species with different phloem loading strategies for the response of photosynthesis to elevated carbon dioxide concentration. We did not find evidence for fundamental differences in species' responses to elevated carbon dioxide concentration based on phloem loading strategy. All species showed large stimulations in photosynthesis when grown and measured at elevated carbon dioxide concentration, as well as greater starch accumulation in the leaves. From this work, we cannot conclude that phloem loading strategy is a key determinant of plant response to elevated carbon dioxide concentration.

Technical Abstract: Species have different strategies for loading sugars into the phloem, which vary in the route that sugars take to enter the phloem and the energetics of sugar accumulation. Species with passive phloem loading are hypothesized to have less flexibility in response to changes in some environmental conditions because sucrose export from mesophyll cells is dependent on fixed anatomical plasmodesmatal connections. However, the influence of different phloem loading strategies on the response of plant carbon metabolism to rising atmospheric CO2 concentrations is unclear, despite the significant and widespread impacts of rising CO2 on plants. Over three field seasons, five species with apoplastic loading, passive loading, or polymer-trapping were grown at ambient and elevated CO2 concentration in Free Air Concentration Enrichment (FACE) plots. Light-saturated rate of photosynthetic CO2 uptake, photosynthetic capacity, leaf carbohydrate content, and leaf anatomy were measured and compared among the different species. All five species showed significant stimulation in rates of midday photosynthetic CO2 uptake by elevated [CO2] even though the two passive loading species showed significant down-regulation of maximum Rubisco carboxylation capacity at elevated [CO2]. There was a trend toward greater starch accumulation at elevated [CO2] in all species, and none of the species showed significant changes in leaf anatomical characteristics at elevated [CO2]. From this study, we cannot conclude that phloem loading strategy is a key determinant of plant response to elevated [CO2], although analysis of additional species or a phylogenetically controlled experiment may be needed to fully test the hypothesis.