COMPARISON OF THE PHOTOSYNTHETIC CAPACITY OF SIBERIAN AND JAPANESE BIRCH SEEDLINGS GROWN IN ELEVATED CO2 AND TEMPERATURE

The effects of increased CO2 and temperature on the photosynthetic cap acity of Siberian white birch and Japanese white birch (Betula platyph ylla Sukatch. and B. platyphylla Sukatch. var. japonica Hara) were mea sured. Birch seedlings were raised with a CO2 partial pressure of 36 /- 0.3 Pa (i.e., ambient) or 70 +/- 0.6 Pa at day/night temperatures o f either 30/16 degrees C or 26/12 degrees C. Siberian birch leaves wer e smaller and thicker than Japanese birch leaves. Water use efficiency and nitrogen use efficiency of Siberian birch grown in the CO2-enrich ed air were higher than those of Japanese birch. Both species showed a physiological adjustment to the growth CO2 partial pressure. Carboxyl ation efficiency and quantum yield of both species grown in CO2-enrich ed air were lower than those of seedlings grown in ambient CO2. The ad aptation of Siberian and Japanese birch to elevated CO2 and temperatur e are discussed in relation to predicted climate change.