Gender-specific responses of Populus tremuloides to atmospheric CO2 enrichment

Dioecious species represent an important component of terrestrial ecosystem s, but little is known about gender-specific responses to elevated atmosphe ric CO2. In an open-top chamber experiment carried out in Michigan, USA, the physiol ogical and growth responses were studied of male and female Populus tremulo ides to elevated CO2 and soil nitrogen concentrations. Male trees had a higher net photosynthetic rate than female trees, but the difference was greater at elevated (25%) than at ambient (13%) CO2. Leaf da rk respiration, averaged across the growing season, tended to be higher in males than in females, and increased significantly in male and female trees with CO2 enrichment. Female trees had higher total biomass than male trees grown in low-nitrogen soil and at ambient CO2, but not in other treatments . Elevated CO2 increased the total biomass of males by 58-66% and of female s by 22-70%. Differing physiological and growth responses to CO2 enrichment by male and female trees should be taken into consideration when predicting the effects of global environmental changes on forest ecosystem structure and function ing.