Document: MIQ-3-31-17

Can trees grown in the shade benefit from low respiration rates at elevated CO₂?

GONZÀLEZ-MELER, M.A.*, E.NAUMBURG, D.ELLSWORTH, J.N.SIEDOW and W.H.SCHLESINGER

Duke University, Durham, NC 27708 USA ¹

Abstract:
Tree leaf respiration is inhibited by 18% as a consequence of growth at elevated CO₂. Most of the inhibition is due to the so-called direct effect, in which the rate of respiration is rapidly and reversibly reduced following an increase in CO₂ concentration. Shade-tolerant trees usually exhibit lower dark respiration rates than shade-intolerant ones. Low respiration rates in the shade are helpful because they lower the light compensation point for photosynthesis enhancing the plant carbon balance. Reduction in rates of dark respiration by elevated CO₂ in shade-grown plants will contribute to enhance the plant carbon balance by lowering the light compensation point, particularly in shade-intolerant species where respiration rates are maximal. However, if elevated CO₂ inhibits the respiratory production of ATP, vital processes such as carbohydrate transport, might be limited and growth subsequently affected, particularly in the shade tolerant species where respiration is minimal. We studied leaf respiratory responses of two shade-tolerant and two shade-intolerant species to elevated CO₂ in a Duke pine forest understory under free air CO₂ enrichment. We measured respiration by the oxygen isotope fractionation technique to accurately estimate net respiratory ATP yields of leaves. Direct effects of a 200-ppm increase in CO₂ concentration over ambient levels, reduced leaf-level respiration, particularly in the shade-tolerant species irrespective of the CO₂ levels at which plants were grown. CO₂ did not affect dark respiration in all species when rates were measured and compared at the respective growth CO₂ concentration, suggesting the existence of compensatory physiological changes at the leaf level. Despite changes in respiration, elevated CO₂ did not affect respiratory ATP yields in the shade tolerant species Cornus florida. However, ATP yields were significantly reduced at elevated CO₂ in the shade intolerant species Liriodendron tulipifera, with negative impacts on growth.

Keywords: Dark respiration, Elevated CO₂, Oxygen isotopic fractionation, shade-tolerant, Shade-intolerant

This abstract is being presented at: 10:45 AM in session:
Oral Session #9: Respiration and Isotopes.