Effect of domestication on Nitrogen use efficiency in foxtail millet

In this research, we utilized six genotypes of millet, each representing a different stage of domestication. These genotypes, closely related genetically, were classified into three categories: wild types, traditional landraces, and modern cultivated varieties.To evaluate the variations in Nitrogen Use Efficiency (NUE) among the six millet genotypes, four levels of nitrogen supplementation were applied: no nitrogen (N0: 0 mg/kg), low nitrogen (N25: 25 mg/kg), medium nitrogen (N50: 50 mg/kg), and high nitrogen (N100: 100 mg/kg). The nitrogen fertilizer, in the form of urea solution, was applied in three split doses starting 21 days after the millet reached the tillering stage, to satisfy the increased nutrient requirements of the plants. Before transplanting, basal applications of potassium dihydrogen phosphate and potassium sulfate were made, providing 50 mg/kg of phosphorus and 200 mg/kg of potassium, respectively. Each treatment had four replications (n=4), totaling 96 pots.Sample Collection:Forty days post-transplanting, all six millet genotypes progressively entered the tasseling stage. At this point, samples were collected by separating the aboveground and underground parts. Aboveground plant materials were first dried in an oven at 105°C for 0.5 hours, then further dried at 70°C to a constant weight. Dry biomass was then measured using a balance (OHRUS PX224ZH, accuracy of 0.001 g).Root samples were carefully washed and then scanned using a root scanner (Epson Expression 10000 XL). The scanned images were analyzed with 'winrhizo 2019a' root imaging analysis software to evaluate root characteristics. Root samples were recollected and dried as described above. After determining dry biomass, all dried above- and below-ground samples were ground and prepared for nitrogen content analysis.Plant nitrogen content was determined following the Kjeldahl method (Matejovic, 2023). Briefly, 0.1 g of the dried and ground shoot and root sample was weighed, and 5 ml of H2SO4 was added. The mixture was boiled until clear and then diluted with distilled water to a final volume of 50 ml. Subsequently, 5 ml of the prepared solution were taken for nitrogen content determination using the Kjeldahl apparatus (SONNEN K1305A).Nitrogen accumulation and NUE were calculated as follows:SNA (mg) = SNC (%) × SB (g)RNA (mg) = RNC (%) × RB (g)PTN (mg) = SNA (mg) + RNA (mg)NUE (%) = (PTNn (mg) - PTNn0 (mg)) / (ANn (mg)) × 100Where SNA, RNA, and PTN represent nitrogen accumulation in the shoot, root, and entire plant, respectively. SNC and RNC refer to nitrogen content in the shoot and root, while SB and RB represent the respective dry biomasses. PTNn and PTNn0 correspond to the total plant nitrogen accumulation with and without nitrogen supplementation (control, N0), and ANn denotes the amount of nitrogen added in the nitrogen addition treatment.Data processing and statistical analysis were conducted using IBM SPSS Statistics version 27 software.Data tables include experimental treatments (domestication atage, genotypes, number of replicates) and data for the aforementioned indices, comprising a total of 15 columns.