ALLOCATION PATTERNS IN 2 TROPICAL VINES IN RESPONSE TO INCREASED ATMOSPHERIC CO-2

1. Our study addresses two questions. (a) When net primary productivity increases in tropical vines, is there an increasing allocation of the gains to growth in height? (b) Are allocation patterns of vines from different types of tropical forests similar or different? 2. We chose congeneric tuberous vines from two types of tropical forest (Psiguria racemosa from tropical premontane moist forest and Psiguria umbrosa from tropical dry forest) and grew seedlings at three concentrations of ambient CO2 in controlled environment chambers. 3. Both species increased markedly in height: average height of Psiguria racemosa increased 5.5 times at 1000 mumol mol-1 CO2, and average height of Psiguria umbrosa increased 7.1 times, compared to plants at 350 mumol mol-1 CO2. In Psiguria racemosa, biomass allocation to shoot growth relative to root growth increased from 55% at 350 mumol mol-1 CO2 to 78% at 1000 mumol mol-1 CO2, whereas allocation ratios remained constant in Psiguria umbrosa. 4. Differences in allocation patterns may reflect adaptive responses to environmental constraints imposed by different habitats. For Psiguria umbrosa, which is deciduous and often dies back during the dry season, allocation to root biomass may be important for the development of storage root tissue that may affect future growth and height.