Comparison of the photosynthetic capacity of Siberian and Japanese birch seedlings grown in elevated CO2 and temperature

The effects of increased CO 2 and temperature on the photosynthetic capacity of Siberian white birch and Japanese white birch (Betula platyphylla Sukatch. and B. platyphylla Sukatch. var. japonica Hara) were measured. Birch seedlings were raised with a CO 2 partial pressure of 36 ± 0.3 Pa (i.e., ambient) or 70 ± 0.6 Pa at day/night temperatures of either 30/16 °C or 26/12 °C. Siberian birch leaves were smaller and thicker than Japanese birch leaves. Water use efficiency and nitrogen use efficiency of Siberian birch grown in the CO 2 -enriched air were higher than those of Japanese birch. Both species showed a physiological adjustment to the growth CO 2 partial pressure. Carboxylation efficiency and quantum yield of both species grown in CO 2 -enriched air were lower than those of seedlings grown in ambient CO 2 . The adaptation of Siberian and Japanese birch to elevated CO 2 and temperature are discussed in relation to predicted climate change.