The interaction of relative air humidity and carbon dioxide enrichment in the growth of Chrysanthemum × morifolium Ramat

Abstract

Plants of Chrysanthemum × morifolium cultivar ‘Fiesta’ were grown hydroponically for 6 weeks in growth chambers at relative humidity (RH) levels of 50 and 95% and CO 2 levels of 340 and 940 μl l −1 in a Latin square combination. High RH as well as high CO 2 resulted in increased relative growth rate (RGR), increased dry weight of leaves, stems and roots, and increased leaf area on main and lateral stems during the first 2 weeks of growth. During this period, high CO 2 levels interacted to stimulate the RH effects. During the third to sixth weeks of growth, the interaction of RH and CO 2 was either lost or, as in the case of RGR and root dry weight, reversed in such a way that a negative effect of high CO 2 at high RG was found. At 6 weeks there were positive main effects of RH and CO 2, but no interaction on plant height, number of leaves on lateral shoots, number of lateral shoots, and length of lateral shoots. The shoot to root dry weight ratio increased at high RH. Water consumption of plants decreased sharply at high RH and moderately at the high CO 2 level. Stomatal aperture was larger at high RH, but smaller at the high CO 2 level. It is concluded that increased plant growth resulting from increased RH might be caused by an increase in stomatal aperture which in turn facilitates CO 2 absorption and utilization.