Effects of soil temperature on the carbon exchange of taiga seedlings. II. Photosynthesis, respiration, and conductance

Potted seedlings of Poputustremutoides Michx., Populusbalsamifera L., Alnuscrispa (Ait.) Pursh., and Betulapapyrifera Marsh., hardwoods of the taiga of interior Alaska, were placed under soil-temperature treatments of 5, 15, and 25 °C with plant tops under a growth-room regime of 20-h day length and day–night air temperatures of 25 and 20 °C, respectively. Photosynthesis showed a differential soil-temperature effect among the species. Maximum photosynthetic rates of 9.5 mg CO2•h−1•dm−2 were observed for P. tremuloides at 25 °C soil and 25 °C air temperature; 9.3 mg CO2•h−1•dm−2 for P. balsamifera at the same temperature combination; and 7.8 mg CO2•h−1•dm−2 for A. crispa at 25 °C air temperature and the lowest soil-temperature treatment, 5 °C. The maximum photosynthetic rate observed for B. papyrifera was 4.9 mg CO2•h−1•dm−2 at 25 °C soil temperature and 20 °C air temperature; low values being due to nonsaturating light conditions. Both leaf dark respiration and conductance were reduced by the 5 °C soil-te...