Uptake of Nitrogen‐15 by Cotton under Salt Stress

Evidence was gathered to evaluate the effect of salt stress on 15 N absorption rate by plants, to indicate how plant parts (roots and shoots) react to NaCl stress conditions. Nitrogen ( 15 NH 4 ) absorption studies were on cotton ( Gossypium hirsutum L.) grown in complete Hoagland nutrient solution in pots with various NaCl concentrations (0, −0.4, −0.8 and −1.2 MPa osmotic potentials). Low and medium levels of salinity (−0.4 and −0.8 MPa) failed to exhibit a significant effect on the 15 N absorption rate, while high levels of salinity (−1.2 MPa) resulted in substantial reduction of 15 N absorption rate. Concentration of 15 N in plants was significantly higher under moderate salinity stress than in the controls. Absorption rate of water significantly decreased with increasing salinity levels, and was directly proportional to plant growth and total dry matter production. Water uptake rate and plant growth were affected to a greater extent than 15 N absorption rate. The effect of salinity was more pronounced at vegetative than at reproductive stages of growth. Nitrogen concentration was greater in roots than shoots.