TITLE:
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
AUTHORS:
Jie He, Lin Qin, Sing Kong Lee
KEYWORDS:
Lettuce, Nitrate Assimilation, Nitrate Uptake, Root Morphology, Root-Zone CO2, Root-Zone Temperature
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.7 No.14,
September
29,
2016
ABSTRACT: 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.