Effect of N Source on Growth and N Uptake of Hippeastrum Using ¹⁵N Tracers

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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 ¹⁵NO₃⁻ + 2.5 mM NH₄⁺ as treatment 1 (T1), 2) 2.5 mM NO₃⁻ + 2.5 mM ¹⁵NH₄⁺ as treatment 2 (T2), 3) 5 mM ¹⁵NO₃⁻ as treatment 3 (T3), and 4) 5 mM ¹⁵NH₄⁺ as treatment 4 (T4). A ¹⁵N-labelled 30 mL nutrient solution was drenched on plant pots (per time per pot). Plants were supplied with the ¹⁵N 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 NO₃⁻ (T3) had a higher total N content than plants supplied with a mixed form of N (T1, T2) or solely NH₄⁺ (T4). In addition, plants supplied solely with NO₃⁻ (T3) had a higher N distribution in leaves than plants supplied with a mixed N source (T1, T2) and solely NH₄⁺ (T4). At 15 weeks after planting (Stage 3), a higher ¹⁵N use efficiency (¹⁵NUE) was observed in plants supplied with a mixed N source (T1, T2) and 5 mM ¹⁵NO₃⁻ (T3) in comparison with those supplied solely with NH₄⁺ (T4). Scales were a major site of ¹⁵N distribution in Hippeastrum at Stage 1. Nevertheless, most ¹⁵N at Stage 2 and 3 was found in the roots + basal plate and leaves, respectively.