Changes in nitrate accumulation and growth of endive plants during light period as affected by nitrogen level and form

Endive plants (Cichorium endivia L. var. crispum Hegi) were hydroponically grown in a growth chamber to assess, 7 and 14 days after beginning of treatments (DAT), the variation of leaf nitrate (NO3) accumulation and growth during the light period in relation to both nitrogen (N) availability (8 and 16 mM) and form percentage ratio [50:50 and 0:100 ammonium (NH4):NO3] in the nutrient solution. Both 7 and 14 DAT, fresh weight and leaf area linearly increased during the light period without influence of N treatments. Dry matter (d.m.) percentage increased over the 12 hours of light. Leaf NO3 concentration decreased during the light period more with 50:50 than with 0:100 NH4:NO3 ratio: 7 DAT NO3 decreased by 25% with the former N treatment and only by 4% with the latter. After 7 days more, the difference between the two N form ratios was more evident: NO3 decreased by 12% with the mixed N form, while increased by 10% with 100% NO3-N in the nutrient solution. Nitrate leaf concentration was higher with 16 mM compared to 8 mM of NO3-N (11.3 and 8.5 g/100 g of d.m., respectively, 14 DAT). Total N leaf content was higher with 16 than with 8 mM of NO3-N in the nutrient solution and was not influenced by the two N form ratios. Chloride (Cl) leaf concentration was higher with 8 that with 16 mM of N and more with the 50:50 than 0:100 NH4:NO3 ratio.