Previous studies on dwarf bean plants have found a very limited growth response to CO₂ enrichment (Jolliffe and Ehret, 1985; Ehret and Jolliffe, 1985b). There was no increase in leaf area, and leaf injury was observed after about three weeks of CO₂ enrichment (Ehret and Jolliffe, 1985a). Although dry weight was increased, the increase may be limited due to restricted carbon utilization (e.g. no increases in leaf area). In this study, non-photosynthetic limitations, such as the partitioning of

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... y matter among plant parts, the partitioning of carbon among photosynthetic end products, and the interactive effects of nutrient and carbon supply on growth, that may contribute to the observed growth responses were investigated. Bean plants responded to CO₂ enrichment by increasing their total dry weights. This weight increase was caused by higher growth rate, at least at early growth stages, and higher unit leaf rate. The dry weight increase was mainly in the leaves, and was not evenly distributed among all plant parts. Leaf expansion and branching were not enhanced by CO₂ enrichment. The differential effects of CO₂ enrichment on growth of different parts caused significant increases in specific leaf weight and shoot root ratio, and a decrease in leaf area ratio. These results indicated that the bean plants used in this study have a limited ability to utilize the extra carbon that was fixed under CO₂ enrichment. There were small increases in glucose, fructose, and sucrose concentrations early in the CO₂ treatments. These increases became much larger after three weeks of CO₂ enrichment. The timing of the higher increases in leaf soluble sugars coincided with the timing of increases in stem and roots dry weight. There was also a large increase in starch concentration shortly after plants were transfered to CO₂ enriched condition. The higher starch concentration accounted for the majority of the weight increase in CO₂ enriched leaves, and this starch level was maintained for several days after plants were switched back [...]