ANALYSIS OF THE GROWTH RESPONSES OF BEAN PLANTS TO ELEVATED CO₂ CONCENTRATIONS

The objective of this study was to use modern methods of plant growth analysis to investigate effects of CO₂ enrichment on some components of vegetative growth. Bean plants (Phaseolus vulgaris L. cv. 'Pure Gold Wax') were grown in controlled environment chambers at 6 CO₂ concentrations ranging from 340 ppm (0.62 g m^-3) to 3 000 ppm (5.43 g m^-3). CO₂ enrichment treatments were continuous and commenced 11 d after planting. Measurements made on replicate plants harvested during the course of growth provided the primary data for plant growth analysis. Cubic spline regressions were fitted to the primary data, and the resulting growth curves were used to evaluate plant performance under different CO₂ regimes. Dry weight per plant increased with increasing CO₂ concentration up to 1 200 ppm and remained nearly constant above that level. Biomass duration accordingly exhibited a similar CO₂ concentration response, but leaf area accumulation was much less sensitive to CO₂. Most growth indices responded to CO₂ enrichment, and one of the most prominent effects was a rapid and sustained decrease in specific leaf area. This effect was evident in all leaf components; hence, the ability to export additional dry weight accumulated in CO₂-enriched leaves may be limited.