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Title: Root morphology, productivity, and photosynthesis of aeroponically grown ice plants (Mesembryanthemum crystallinum) with different nutrient spraying intervals

He Jie

National Institute of Education, Nanyang Technological University, Singapore

Biography

Dr. He Jie obtained her Ph.D. from Macquarie University, Australia in 1991. She is currently an Associate Professor at Nanyang Technological University, Singapore. She has more than 30 years of research experience in plant physiology. She has been actively involved in the research on responses of plants to environmental stresses (temperature, drought, light, UVB radiation). Her research interests are 1) photosynthesis (chlorophyll fluorescence, Rubisco protein); 2) shoot-root communication (C partitioning, nutrient uptake and N metabolism; 3) effects of root-zone temperature on aeroponically grown temperate crops in the tropics; 4) impacts of LED quality and quantity on photosynthesis and vegetable production.

Abstract

Mesembryanthemum crystallinum (common name: ice plant) is a succulent plant native to South Africa. It has high nutritional values and has been successfully grown in the greenhouse in Japan and Taiwan undercooling temperature. Recently we have also grown this plant successfully in a  tropical greenhouse by cooling the root-zone only or indoor at cooling temperature under different combinations of LED-lighting.  Our results also showed that this facultative CAM (crassulacean acid metabolism) plant performed C3 photosynthesis when supplied with adequate water. Although it is drought- and salt-tolerant species, there is very little work done on the effects of water and nutrient supply on this vegetable crop. This project aimed to investigate the impacts of nutrient spraying intervals on root morphology, productivity, and photosynthesis. In this project, all seedlings were grown for 4 weeks in small trays before transferring to aeroponic systems with different nutrient spraying intervals. In terms of root morphology and productivity, the longer nutrient spraying intervals such as 30, 60 and 240 min resulted in reductions of total root length, total root surface area and the total number of root tips, and a smaller mass of root and shoot compared to a shorter interval of 5 min. A decline in photosynthetic light use efficiency measured by chlorophyll fluorescence parameters demonstrated that plants grown under longer nutrient spraying intervals utilized lesser light energy and did not dissipate heat as effectively as those sprayed with nutrient solution for 5 min interval. Photosynthetic CO2 assimilation rate (Asat), stomatal conductance and internal CO2 concentration were significantly reduced for plants grown under 240 min nutrient spraying interval, indicating signs of drought stress. All other plants had similar values of saturated photosynthetic O2 evolution rate (Pmax), Asat, total reduced nitrogen and Rubisco concentrations. However, higher total chlorophyll concentration in plants grown under 240 min nutrient spraying interval imply that chlorophyll could be a mean of storing nitrogen.