Author(s)

Jie He^*, Lin Qin, Sing Kong Lee

Natural Sciences and Science Education Academic Group, National Institute of Education, Nanyang Technological University, Singapore.

This paper investigated the effects of root-zone (RZ) CO₂ concentration ([CO₂]) on root morphology and growth, nitrate (NO₃^-) uptake and assimilation of lettuce plants at different root-zone temperatures (RZT). Elevated RZ [CO₂] stimulated root development, root and shoot growth compared to ambient RZ [CO₂]. The greatest increase in root growth was observed in plants grown under elevated RZ [CO₂] of 50,000 ppm. However, RZ [CO₂] of 10,000 ppm was sufficient to achieve the maximal leaf area and shoot productivity. Lettuce plants exhibited faster shoot and root growth at 20°C-RZT than at ambient (A)-RZT. However, under elevated RZ [CO₂], the magnitude of increased growth was greater at A-RZT than at 20°C-RZT. Compared to RZ [CO₂] of 360 ppm, elevated RZ [CO₂] of 10,000 ppm increased NO₃^- accumulation and nitrate reductase activity (NRA) in both leaves and roots. NO₃^- concentrations of leaf and root were higher at 20°C-RZT than at A-RZT in all plants. NRA was higher in root than in leaf especially under A-RZT. The total reduced nitrogen (TRN) concentration was significantly higher in plants grown under elevated RZ [CO₂] of 10,000 ppm than under ambient RZ [CO₂] of 360 ppm with greater concentration in 20°C-RZT plants than in A-RZT plants. These results imply that elevated RZ [CO₂] significantly affected root morphology, root and shoot growth and N metabolism of temperate lettuce with greater impacts at A-RZT than at 20°C-RZT. These findings have practical significance to vegetable production by growing the vegetable crops at cool-RZT with elevated RZ [CO₂] to enhance its productivity.

Lettuce, Nitrate Assimilation, Nitrate Uptake, Root Morphology, Root-Zone CO₂, Root-Zone Temperature

He, J. , Qin, L. and Lee, S. (2016) Root Morphology, Plant Growth, Nitrate Accumulation and Nitrogen Metabolism of Temperate Lettuce Grown in the Tropics with Elevated Root-Zone CO₂ at Different Root-Zone Temperatures. American Journal of Plant Sciences, 7, 1821-1833. doi: 10.4236/ajps.2016.714169.