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

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Abstract
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 CO2 enrichment in open‐top field chambers. Despite the absence of a CO2 effect on individual leaf expansion or specific growth rate (SGR), increasing the CO2 concentration to ambient +150 or +300 cm3 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 CO2 g−1 dry mass compared with 572 and 570 mg CO2 g−1 for leaves grown at the two higher CO2 concentrations. Leaves from the elevated CO2 treatments had an average maintenance respiration coefficient of 88 mg CO2 g−1 dry mass d−1 compared with 135 mg CO2 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 cm3 m−3 CO2 throughout its 50‐d lifespan compared with one grown at ambient CO2 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 CO2 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 CO2 remains unresolved.