Effect of N Source on Growth and N Uptake of Hippeastrum Using¹⁵N Tracers

Abstract

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 mM15NO3 − + 2.5 mM NH4 + as treatment 1 (T1), 2) 2.5 mM NO3 − + 2.5 mM15NH4 + as treatment 2 (T2), 3) 5 mM15NO3 − as treatment 3 (T3), and 4) 5 mM15NH4 + as treatment 4 (T4). A15N-labelled 30 mL nutrient solution was drenched on plant pots (per time per pot). Plants were supplied with the15N 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 higher15N use efficiency (15NUE) was observed in plants supplied with a mixed N source (T1, T2) and 5 mM15NO3 − (T3) in comparison with those supplied solely with NH4 + (T4). Scales were a major site of15N distribution in Hippeastrum at Stage 1. Nevertheless, most15N at Stage 2 and 3 was found in the roots + basal plate and leaves, respectively.