Water cooling temperature treatment suppresses growth, development, and nitrate reductase enzyme activity in sacred lotus (Nelumbo nucifera Gaertn.)

In Thailand, the normal growth and flower quality of sacred lotus are still limited due to low temperature condition in mild winter. This might partially be an obstacle to promote this exotic aqua-geophyte as year round cut flower. To clarify the effects of water cooling temperature (WCT) on its growth, an experiment was conducted during 2 months in a completely randomized design with 3 different water temperatures T1: ambient water temperature (control), T2: WCT 20°C, and T3: WCT 15°C under natural conditions in a greenhouse. Each cutting stolon was grown up to reach 3 up-right leaves growing stage in a plastic pot containing commercial clay as substrate media, prior to transfer in a 3×5 m concrete tank filled to 3/4 of the container level with tap water. Then, all plants were continuing to receive water cooling condition for 12 h overnight. All decreased WCT at night suppresses some aboveground growth in terms of leaf number, total leaf area and dry weight. However, the opposite result for underground growth was found as reduced WCT accelerate increased yields of sacred lotus rhizomes (total stolon length, quantities of total node and internode number). Water cooling temperature at 15°C gave the lowest nitrate reductase enzyme activity associated with nitrogen assimilation. No flowering was observed under each WCT condition during the experimental period. This finding might confirm the role of low temperature for inducing rhizome dormancy, resulting in poor growth and flower quality of off-season sacred lotus production.