2002 Volume 19 Issue 1 Pages 25-31
A newly designed free-air CO_2 enrichment (FACE) system using pure CO_2 was developed and applied to a paddy field in a cool-temperate region in northern Japan. Structural changes of weed communities in the rice paddy field under ambient and FACE (ambient+200μmol mol^<-1> CO_2) conditions were examined. Biomass of planktonic algae was small throughout the experimental period due to shallow and variable depth of flooding water in the paddy field. Elevated CO_2 slightly increased the biomass of algae, but the increment was not statistically significant. CO_2 fertilization effect on the biomass of floating weeds (Lemna perpusilla and Spirodela polyrhiza) was 3-fold in August, and 1.6-fold in September in terms of ability to exhibit vegetative propagation. In contrast, community structures of the paddy weeds (emergent and terrestrial plants) under FACE condition did not differ from that of ambient condition. CO_2 fertilization effect on the paddy weeds might be reduced by frequent human weeding and/or nutrient limitation by growth of rice plants.
