Nitrogen source and supply level impact water uptake, yield, and nutrient status of golden thistle in a soilless culture

•A NH4-N/total-N of 0.1 at a total-N of 14.2 mM maximizes yield in soilless S. hispanicus crops.•High NH4+ supply reduced marketable yield due to impairment of the root visual appearance.•High NH4+ supply improved the root zone pH but decreased the stomatal conductance.•The uptake concentrations were affected by both the N source and the total-N level. Soilless production of wild edible species is a modern and economically attractive cultivation option, given their high nutritional and culinary properties. However, while the specific nutritional needs and especially nitrogen N requirements are well known for commercial vegetable species, thus ensuring high yield and quality, these aspects are still not well studied for wild edible greens such as golden thistle (Scolymus hispanicus, L.). Considering this background, a factorial experiment was conducted aiming to assess the impact of both the level and the source of the supplied N (NH4+ : NO3− ratio) on the agronomic characteristics, macronutrient uptake, and photosynthetic capacity of S.hispanicus L. More specifically, four nutrient solution treatments were applied by combining two levels of total-N supply (7.2 mM N or 14.2 mM N) with two NH4+-N : total-N supply ratios, particularly 0.1 and 0.2, respectively, in a 2-factorial design. A total-N supply of 14.2 mM in the supplied nutrient solution combined with an NH4+-N : total-N ratio of 0.1, significantly increased the cumulative water uptake, number of leaves, and shoot fresh and dry weight, compared with 7.2 mM N, by 22.25%, 34.80%, 58.58%, 32.18%, respectively, as well as compared with the same N level (14.2 mM N) with an NH4+-N/total-N ratio of 0.2, by 21.20%, 23.80%, 22.44%, 16.24%, respectively. The combination of high total-N and high NH4+-N/total-N ratio maintained the root zone pH more closely to the target range (5.5–6.5) but decreased stomatal conductance and increased the incidence of rot in tuberous root, thereby decreasing marketable yield. The tissue nutrient levels were only marginally influenced by the differences in N source and supply level, except for N which reflected the differences in total N supply. A N supply level of about 14.2 mM of which only 1.40 mM was ammonium, proved to be the best strategy for high marketable production in the soilless S. hispanicus L. crop.