Growth and maintenance respiration in leaves of Liriodendron tulipifera L. exposed to long‐term carbon dioxide enrichment in the field

summary Specific respiration rate (SRR) was mathematically partitioned into its growth and maintenance components for leaves of yellow‐poplar ( Liriodendron tulipifera L.) after 3 yr of CO 2 enrichment in open‐top field chambers. Despite the absence of a CO 2 effect on individual leaf expansion or specific growth rate (SGR), increasing the CO 2 concentration to ambient +150 or +300 cm 3 m −3 decreased SRR by 28 to 45% compared with ambient‐grown controls. These lower leaf respiration rates were correlated with reduced leaf nitrogen concentrations. As described by the two‐component model of growth and maintenance respiration, SRR was a linear function of SGR. Ambient‐grown leaves had a growth respiration coefficient of 704 mg CO 2 g −1 dry mass compared with 572 and 570 mg CO 2 g −1 for leaves grown at the two higher CO 2 concentrations. Leaves from the elevated CO 2 treatments had an average maintenance respiration coefficient of 88 mg CO 2 g −1 dry mass d −1 compared with 135 mg CO 2 g −1 d −1 for leaves from the ambient treatment. Incorporating these growth and maintenance coefficients into a leaf growth simulation model indicated that total respiration would be reduced by 21 to 26 % for a leaf exposed to + 150 or + 300 cm 3 m −3 CO 2 throughout its 50‐d lifespan compared with one grown at ambient CO 2 conditions. Reductions in total respiration were dominated by a lower rate of maintenance respiration, while the contribution of a lower specific rate of growth respiration was largely offset by a greater dry mass for leaves grown at elevated CO 2 concentrations. Although reductions in the respiratory loss of carbon could be beneficial, respiration is unlikely to decrease without a concomitant decrease in other metabolic processes. Whether these reductions are beneficial or detrimental to the long‐term growth of plants exposed to elevated CO 2 remains unresolved.