Abstracts Biological Sciences

Nitrogen uptake by wheat (Triticum aestivum VILL., Host) as a function of root temperature and plant water stress

by Ali Reza Sepaskhah

The effect of soil temperature and plant water stress on nitrogen uptake, growth rate and transpiration rate of wheat (Triticum aestivum VILL. , Host) seedlings was studied. A special apparatus for the control of plant water stress and root temperature was used. Leaf area was measured by the air flow planimeter technique. Dry matter weight was determined with a Mettler balance after oven drying of the plant material. Nitrogen concentration in shoots and roots was determined by the micro-Kjeldahl procedure. The transpiration rate was obtained with a constant-water level graduated burette device operating on the principle of a Mariotte bottle. Growth rate of shoots and roots was slowest at the extreme temperatures with a maximum rate of growth occurring around a root temperature of 24° C. The growth rate was higher at a plant water stress of 0.35 bar than at a plant water stress of 2.5 bars. Rates of transpiration decreased steadily with increasing plant water stress. The increase of transpiration rate with root temperature increase was attributed to the change of water viscosity and increased root cell membrane permeability. The nitrogen content of roots and shoots increased as root temperatures increased from 10.0 to 25.0°C, while there was no significant difference at plant water stresses of 0.35 and 2.5 bars. The increase in rate of nitrogen uptake was found to be proportional to the increase in rate of root growth. The same proportionality described a decrease in the rate of nitrogen uptake as a result of decreased rate of root growth. The rate of leaf area increase was found to be related to the rate of dry matter increase of the shoot. This relation was the same at all root temperatures and plant water stresses considered.