Effects of CO₂ enrichment and potassium supply on growth and inorganic nutrition of chrysanthemum (Dendranthema grandiflora Tzvelev)

Beyond the effects of photosynthesis, plant responses to CO₂ enrichment are modified by secondary environmental factors and internal processes, including mineral relations and carbon partitioning. Leaf abnormalities sometimes develop under long-term CO₂ enrichment, and previous research has correlated them with altered nutrient requirements and distribution. To explore the roles of CO₂ enrichment on the development of leaf abnormalities, three experiments were performed on chrysanthemum (Dendranthema grandiflora Tzvelev) plants cv 'Envy'. CO₂ enrichment and K+ supply effects on growth, carbon partitioning, and the inorganic nutrient contents in plants were studied. CO₂ enrichment increased plant dry mass, mainly due to increased leaf dry mass. In CO₂ enriched plants, increased leaf area of branch leaves resulted in an increase in total leaf area. There was no significant further increase above 1200A L L⁻¹ CO₂. Leaf starch concentration was increased by CO₂ enrichment, although there was no evidence of excessive starch accumulation. CO₂ enrichment did not have a significant effect on the leaf concentrations of sucrose, glucose, fructose or protein. Total leaf content of inorganic nutrients was not changed by CO₂ enrichment. CO₂ enrichment decreased the starch-corrected concentrations of some nutrients in leaves borne on main stems. That change was significant for K, Ca and Mn, and also for the ratio of Mn to Zn. In leaves borne on the lower part of branches, CO₂ enrichment induced a slight reduction in N concentration. Interactions between CO₂ enrichment and K supply on the nutrient relations of plants were seldom detected. Increasing K limited leaf dry mass accumulation and leaf area production, reduced nutrient concentrations, and induced leaf chlorosis. The interpretation of K effects was restricted by the possible detrimental effect of acetic acid. This negative effect was probably enhanced by daily drifts in the pH of nutrient solutions. Both acetic acid additions and the size of pH drifts increased with increasing K supply. A possible beneficial effect of Na, when K supply was low, further confounded the interpretation of K supply effects. Interveinal chlorosis appeared on both the upper most leaves of main stems and the lower leaves borne on branches, after one week of CO₂ enrichment. It was more pronounced in the latter. Leaf chlorosis decreased toward the bottom of main stems, and toward the top of branches. Increasing K supply enhanced chlorosis in both CO₂ enriched and unenriched plants. No relationship was detected between leaf chlorosis and leaf starch concentration or leaf temperature. Reduced leaf concentration of Mn coupled with alterations in the Mn to Zn ratio, and the appearance and distribution of symptoms, suggest that Mn deficiency played a role in the induction of chlorosis by CO₂ enrichment. However, other nutrients, such as K or N, or non-nutritional factors could be involved in the disorder. These studies confirmed that CO₂ enrichment reduces leaf nutrient concentration and makes plants more susceptible to nutrient stresses. The importance of inorganic nutrition in the regulation of plant responses to CO₂ enrichment was also verified.

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