Acclimation of respiration to temperature and CO2 in seedlings of boreal tree species in relation to plant size and relative growth rate

Abstract

Summary: The role of acclimation of dark respiration to temperature and CO 2 concentration and its relationship to growth are critical in determining plant response to predicted global change. We explored temperature acclimation of respiration in seedlings of tree species of the North American boreal forest. Populus tremuloides, Betula papyrifera, Larix laricina, Pinus banksiana, and Picea mariana plants were grown from seed in controlled‐environments at current and elevated concentrations of CO 2 (370 and 580 μmol mol–1) in combination with three temperature treatments of 18/12, 24/18, and 30/24 °C (light/dark period). Specific respiration rates of roots and shoots acclimated to temperature, damping increases in rates across growth‐temperature environments compared to short‐term temperature responses. Compared at a standard temperature, root and shoot respiration rates were, on average, 40% lower in plants grown at the highest compared to lowest growth temperature. Broad‐leaved species had a lower degree of temperature acclimation of respiration than did the conifers. Among species and treatment combinations, rates of respiration were linearly related to size and relative growth rate, and relationships were comparable among growth environments. Specific respiration rates and whole‐plant respiratory CO 2 efflux as a proportion of daily net CO 2 uptake increased at higher growth temperatures, but were minimally affected by CO 2 concentration. Whole‐plant specific respiration rates were two to three times higher in broad‐leaved than coniferous species. However, compared to faster‐growing broad‐leaved species, slower‐growing conifers lost a larger proportion of net daily CO 2 uptake as respiratory CO 2 efflux, especially in roots. Interspecific variation in acclimation responses of dark respiration to temperature is more important than acclimation of respiration to CO 2 enrichment in modifying tree seedling growth responses to projected increases in CO 2 concentration and temperature.