This research aims to determine growth and deficiency patterns as well as antioxidative potentials of Japanese mint (Mentha arvensis) hydroponically grown under limited macronutrients and micronutrients. The experiment was conducted for 60 days after transplanting in an evaporative greenhouse (avg temp = 28–30 °C, 60–65 %RH), using deep water culture technique. Plants were grown in nutrient solution consisting of complete Hoagland’s solution (CTRL), and nutrient solutions lacking one of the following macronutrients and micronutrients: nitrogen (-N), phosphorus (-P), potassium (-K), iron (-Fe), manganese (-Mn), and copper (-Cu). The deficiency symptoms, growth patterns, and stress response mechanism were followed. All treatments except for the CTRL induced deficiency symptoms and physiological changes. Macronutrient deprivation reduced growth determined by the morphological parameters while micronutrient omission had no effect except for no iron treatment. The result showed that potassium and iron deficiencies had foremost adversely effect on growth of Japanese mint. Under nutrient stress conditions, plant only gave antioxidative responses to phosphorus and potassium deficiencies. However, the negative plant-stress relationship was found for no iron treatment indicating the detoxification mode of plant for lacking of micronutrient.

Nitrate is a major source of the inorganic nitrogen taken up by the roots of plants. Nitrate sources are generally derived from inorganic minerals by an energy-consuming chemical process; as a result, the price of chemical fertilizers is gradually increasing year by year. NO3-N, generated from N2 using the plasma technique, is an alternative method of producing nitrate from the air. Therefore, in this research, we aimed to determine the efficiency of generating NO3-N using plasma-activated water (PAW) to replace nitrates from chemical fertilizer in a nutrient solution. Green oak lettuce (Lactuca sativa L.) was grown in a hydroponics system using the double-pot technique. The plants were supplied with three different nutrient solutions (based on Hoagland’s solution), i.e., T1, no nitrate in the nutrient solution (NO3− = 0); T2, using nitrate sourced from a commercial chemical fertilizer (normal nitrate); and T3, using a nitrate source generated using the pinhole plasma jet technique (plasma nitrate). The other macronutrients and micronutrients in each treatment were equally supplied. The results show that, at the harvested stage (21 days after the plants received treatment), the no-nitrate (T1) treatment provided lower growth and yields. Moreover, compared with the normal nitrate (T2) and plasma nitrate (T3), the results indicate that most growth and yields showed no statistical differences. In terms of nitrate accumulation within plants, it was found that the normal nitrate treatment (T2) had the highest levels of nitrate accumulation, in both the underground and aboveground parts of green oak lettuce. These results confirmed that plasma nitrate could be an alternative source of nitrate N which provided a safer way for the environment and human health in terms of nitrate accumulation. In addition, data related to the chemical analysis of free amino acid concentrations in each treatment are discussed in this research.

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Understanding the mechanism of N uptake is of key importance to manage N utilization efficiency. Hippeastrum is a popular geophyte, but its N absorption and translocation characteristics are still not well understood. Therefore, the objective of this study was to assess the effect of different N sources on growth, N uptake and N distribution in Hippeastrum. The experiment was set up in a completely randomized design (CRD) with four different N sources of equal N concentration, i.e., 1) 2.5 mM 15 NO 3 − + 2.5 mM NH 4 + as treatment 1 (T1), 2) 2.5 mM NO 3 − + 2.5 mM 15 NH 4 + as treatment 2 (T2), 3) 5 mM 15 NO 3 − as treatment 3 (T3), and 4) 5 mM 15 NH 4 + as treatment 4 (T4). A 15 N-labelled 30 mL nutrient solution was drenched on plant pots (per time per pot). Plants were supplied with the 15 N solution every two weeks. Plant samples were divided into three stages according to plant growth stage, i.e., Stage 1 (emerging stage-1 WAP), Stage 2 (flowering stage-3 WAP), and Stage 3 (vegetative stage-15 WAP). The results indicated that plants fed with a combined N fertilizer and nitrate had a higher total dry weight than plants supplied solely with ammonium. At Stage 3, the plants supplied with 5 mM NO 3 − (T3) had a higher total N content than plants supplied with a mixed form of N (T1, T2) or solely NH 4 + (T4). In addition, plants supplied solely with NO 3 − (T3) had a higher N distribution in leaves than plants supplied with a mixed N source (T1, T2) and solely NH 4 + (T4). At 15 weeks after planting (Stage 3), a higher 15 N use efficiency ( 15 NUE) was observed in plants supplied with a mixed N source (T1, T2) and 5 mM 15 NO 3 − (T3) in comparison with those supplied solely with NH 4 + (T4). Scales were a major site of 15 N distribution in Hippeastrum at Stage 1. Nevertheless, most 15 N at Stage 2 and 3 was found in the roots + basal plate and leaves, respectively.