Direct and indirect effects of shoot- and/or root-chilling stress on growth, photosynthesis, and osmotic root water uptake in Kalanchoe blossfeldiana Poelln. 'Molly'

Kalanchoe blossfeldiana is the most extensively cultivated flowering potted plant for indoor use in Europe, and it is also used outdoors as a patio and bedding plant. Increased chilling tolerance in K. blossfeldiana is desirable, as it would enhance the marketing potential for outdoor use and allow more energy-efficient greenhouse production. In this study, the effects of shoot-chilling, root-chilling, or whole plant-chilling (4°C/20°C, 20°C/4°C, or 4°C/4°C air temperature /root-zone temperature, respectively) on K. blossfeldiana Poelln. 'Molly' were compared in order to identify the most sensitive physiological processes related to the impairment of growth under low temperatures. As controls, plants were grown at 20°C/20°C. All three chilling treatments severely inhibited plant growth and decreased the net photosynthetic rate (P). Inhibition of P in root-chilled plants was due to stomatal closure, while in shootchilled plants it was related both to stomatal and non-stomatal effects. A low air temperature also caused the accumulation of soluble carbohydrates and cellular membrane damage in the leaves. Root- or whole plant-chilling significantly reduced the composite root hydraulic conductance (CRHC), whereas the decrease in osmotic root water uptake of shoot-chilled plants was unrelated to changes in CRHC. Impaired water uptake led to partial leaf wilting of root-chilled plants at 20°C/4°C. We conclude that the sensitivity of Kalanchoe to low temperatures is linked to both direct and indirect effects of shoot- and/or root-chilling on photosynthetic carbon metabolism and osmotic water uptake by the roots.