Response of lettuce (Lactuca sativa L.) growth to reciprocal root-zone temperature (RZT) transfer at different growth stages

SummaryResponses of Butterhead lettuce (Lactuca sativa L.) to the reciprocal RZT transfer were studied using aeroponic systems under tropical fluctuating aerial temperatures. Lettuce plants were transferred reciprocally between optimum 20°C-RZT and hot ambient-RZT (A-RZT) (25°C to 39°C) at several growth stages (6, 11, 16, 21 and 26 d after transplanting (DAT). Changes in total number of leaves, total leaf area, fresh and dry weights of shoot, were linear correlated with the number of days that plants were grown at 20°C-RZT for both reciprocal RZT transferred plants. These indicate that the longer Butterhead lettuce plants were grown at 20°C-RZT, the higher the productivity. However, plants grown at A-RZT at early stage (i.e. before 11 DAT) and then transferred to 20°C-RZT in the later growth stage (A→20°C-RZT plants) achieved a higher shoot productivity similar to that of the 20°C-RZT plants. Changes in root morphology during the RZT transfer period clearly showed that the development of root system in t...