Rootzone Temperature on N Absorption and Physiology of Cucumber

Increasing nitrogen absorption efficiency reduces use of excessive application of N. The effect of rootzone temperature on nitrogen absorption needs clarification. The experiment was conducted to investigate low (15°C, RTZ1), high (35°C, RTZ2) and optimum (25°C, RTZ3) root zone temperatures and nitrogen 52.5 (ND1), 78.75 (ND2) and 105 (ND0) mg∙L-1 levels on cucumber (Cucumis sativus L.), cv. Super N3, cultured in Johnson nutrient solution. Shoot and root fresh and dry weights, chlorophyll content, maximum photochemical quenching )Fv/Fm(, antioxidant activity, total phenol and nitrate reductase (NR) activity increased with N. Shoot fresh and dry weights, chlorophyll content, total phenol, antioxidant and NR activity was reduced at high and low root zone temperature compared to the optimum temperature. Shoot fresh and dry weights increased in RTZ1 and RTZ2 for the ND2 and ND0 treatments. The SPAD value increased in RZT2 at all nitrogen levels. The highest Fv/Fm occurred at ND0 at all temperature levels. Antioxidant activity increased for the ND0 and ND2 treatments with increasing root zone temperature. Total phenol content increased in ND1 and ND2 at low and high temperatures compared to the optimum temperature, and increased with increasing temperature level in ND0 treatment. The NR activity increased at the high root zone temperature in ND2 and ND0 treatments. The ND0 and ND2 treatments alleviated the root zone temperature effect on cucumber grown in hydroponic culture.