اثر تنش دمای پایین ریشه بر خصوصیات رشد، فتوسنتز و فیزیولوژیکی کاهو در سه سطح نیتروژن

Regarding the differences between shoot and root optimum growth temperature and the impress of temperature on root function specially nutrient absorption this study was aimed to investigate the effect of low root temperature with three nitrogen levels in lettuce. The experiment was conducted in factorial completely randomized trial design with five replication. Treatments were used including three nitrogen levels (100, 75 and 50) % Johnson nutrient solution and two temperature levels (15ºC: stress condition, 25ºC: optimum condition). The experiment was performed in greenhouse of Isfahan University of Technology. Results indicated that by decreasing nitrogen and temperature levels prolin and root exudate phenol in T2×N3 treatment were 98 and 8 % higher than control treatments respectively. Furthermore in photosynthesis rate and stomata conductivity with 80 and 56 % reduction from control treatment the lowest amount of them observed. Also photosynthetic water efficiency and chlorophyll index were 69 and 70 % more than control treatment respectively. Shoot and root fresh weight were 50 % more than other treatments. Under low temperature stress photosynthesis rate, evaporation, stomata conductivity and the amount of phenolic compounds and proline mostly impressed. Based on present results in order to obtain lettuce greatest yield we should satisfied its temperature and nutritional needs but plants will be resistance under stress condition by releasing prolin and phenolic compounds.