Nitrogen and phosphorus uptake kinetics by two blackberry genotypes grown in Florida

This study aimed to investigate N and P acquisition efficiency of two selected blackberry (Rubus fruticosus) cultivars, ‘Natchez’ and ‘Osage’, for Florida’s rapidly expanding commercial production. The seedlings were purchased from a commercial supplier and grown in an aeroponic system with 10% strength Hoagland solution at pH 6.5 for two weeks. After being washed with DI water four times, the seedlings were individually placed in a container with 0.1 mmol L^‑1 CaSO₄ solution for starvation for 72 h. Three individual single-seedling tests were then conducted with three corresponding measuring solutions, each with three replications, containing 0.071 mmol L^‑1 NH₄⁺, 0.071 mmol L^‑1 NO₃^-, and 0.016 mmol L^‑1 H₂PO₄^-, respectively, with 0.1 mmol L^‑1 Ca²⁺ added. The temperature was 23±1°C, relative humidity was 55±3%, and photosynthetic photon flux density (PPFD) was 69 µmol s^‑1 m^‑2. The data were calculated via the nutrient depletion method. The results showed that ‘Osage’ was significantly faster than ‘Natchez’ in influx of each of NH₄⁺, NO₃^-, and H₂PO₄^-, with respective I_max values of 9.37 and 3.09 µmol g^‑1 DW h^‑1 for NH₄⁺, 1.86 and 0.92 µmol g^‑1 DW h^‑1 for NO₃^-, and 1.86 and 0.32 µmol g^‑1 DW h^‑1 for H₂PO₄^-. The corresponding K_m values of ‘Osage’ and ‘Natchez’ were 17.2 and 169.1 µmol L^‑1 for NH₄⁺, 74.5 and 73.7 µmol L^‑1 for NO₃^-, and 4.2 and 18.4 µmol L^‑1 for H₂PO₄^-, respectively. These results indicate that ‘Osage’ has significantly better Michaelis-Menten kinetics coefficients for influx of NH₄⁺, NO₃^-, and H₂PO₄^- than ‘Natchez’.