Effects of Substrate Water Content on Morphology and Physiology of Rosemary, Canadian Columbine, and Cheddar Pink

Two experiments were conducted to determine how different substrate volumetric water contents (θ equals volume of water per volume of substrate) affected morphology and physiology of three popular perennials using a capacitance sensor-automated irrigation system. In the first study, rosemary (Rosmarinus officinalis) was grown at one of eight θ set points ranging from 0.05 to 0.40 L·L−1. In the second study, Canadian columbine (Aquilegia canadensis ‘Pink Lanterns’) and cheddar pink (Dianthus gratianopolitanus ‘Bath’s Pink’) were grown at one of nine θ set points ranging from 0.05 to 0.45 L·L−1. Total leaf number and area as well as shoot fresh and dry weight of rosemary plants grown at θ of 0.20 L·L−1 or greater were approximately twice that of those grown at lower θ. Canadian columbine height increased as θ increased. Leaf area of cheddar pink grown at θ of 0.35 L·L−1 or higher was twice that of plants grown at the lowest θ. Shoot dry weight of Canadian columbine was not significantly affected by θ. Shoot dry weight of cheddar pink responded quadratically to increasing θ and peaked at θ of 0.35 L·L−1. θ also significantly influenced photosynthetic activities; net photosynthetic rate (AN) and stomatal conductance (gs) of Canadian columbine increased with increasing θ. AN of cheddar pink also increased as θ increased. Greater water volumes were applied to maintain higher θ set points. Irrigation water use efficiency (IWUE = shoot dry weight ÷ total amount of water applied per plant) of Canadian columbine and cheddar pink was not influenced by θ. Growth of all three plants was reduced when grown at lower θ; in the case of cheddar pink and Canadian columbine, this was attributable at least in part to reduced AN.