Effect of 700 μmol mol −1CO2 and infection with powdery mildew on the growth and carbon partitioning of barley

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Abstract
Summary: The dry weight of barley plants in 700 μmol mol−1CO2 was increased by 19 d after planting relative to plants grown in 350 μmol mol−1CO2. Infection of the second leaf by powdery mildew led to reduced growth rates in both 350 and 700 μmol mol−1CO2, but the reduction in growth was transitory in 350 μmol mol−1CO2. Neither the allometric coefficient k between shoot and root, nor the leaf weight ratio, was altered by growth in 700 μmol mol−1CO2 or by infection with powdery mildew. The number of tillers produced increased per plant but not per unit d. wt in 700 μmol mol−1CO2. The growth response of barley to increased concentrations of CO2 and/or to infection with powdery mildew was not associated with alterations in net carbon partitioning, so a change in the ratio of photosynthetic to non‐photosynthetic tissue, contributed to neither the growth response of barley to 700 μmol mol−1CO2 nor to infection with powdery mildew. The increase in the growth rate of barley in 700 μmol mol−1CO2 and the reduction in the growth rate after infection occurred at the same time as increased and reduced rates of net photosynthesis respectively.