Integrated Effects of Root-Zone Temperatures and Phosphorus Levels on Aeroponically-Grown Lettuce (Lactuca sativa L.) in the Tropics

In this study, butterhead lettuce (Lactuca sativa L. cv. Baby Butter) plants were grown at three root-zone tem- peratures (RZTs): 25 o C, 30 o C and ambient-RZT (A-RZT) ranging from 26 o C-42 o C while their shoots were maintained at hot ambient temperature ranging from 26 o C-42 o C. Three phosphorus (P) concentrations: -25% P (minus P, 23.25ppm), control (31.00ppm) and +25% P (plus P, 38.75ppm) were supplied to the plants at each RZT using Netherlands Standard Nutrient Solution. Interactions between RZT and P concentrations on productivity, root morphology, maximum photosyn- thetic O2 evolution (Pmax), P uptake and its partitioning between shoot and root were studied. Lettuce plants grown with the plus P concentration at 25 o C-RZT had the highest productivity, highest Pmax, highest shoot and root P concentrations. However, all the root morphological parameters studied were the greatest in plants grown with the minus P at 25 o C-RZT. Higher P concentration in the solution and 25 o C-RZT resulted in higher portion of the absorbed P partitioned to the shoots. Integrated effects of RZT and P concentration on the productivity, root morphology, photosynthesis and P uptake were discussed.