Effect of Temperature, Shading, and Mineral Nutrient on Photosynthesis and Growth of Neoregelia Plug Seedlings

Neoregelia species have long - lasting showy bracts and have been widely used in outdoor and indoor landscaping. Production was long and could be hastened by manipulating environmental conditions and nutrient management to for seedling growth. The objectives of the study were to determine the effects of temperature, light and nutrient solution concentration, and nitrogen and potassium nutrient requirement on leaf growth and photosynthesis. Hybrid seeds of four Neoregelia cross combinations were sown under day/night temperatures of 20/15, 25/20, 30/25, and 35/30oC. Results showed that the time for seeds to reach 50% germination was earlier at 25/20 and 30/25oC than 20/15 and 35/30oC. Maximum germination percentage were lower when sown at 35/30oC. Hybrid seedlings with 4-5 leaves of three Neoregelia cross combinations were grown under various temperatures. Results showed plants had higher whole plant net photosynthesis, shoot and root dry weights, leaf number, leaf area, and SPAD-502 reading value at 25/20 and 30/25oC than at 20/15oC. Plants at 15/13oC showed cooling injury, and all died when grown at 35/30oC. Neoregelia ‘Pink Sensation’ × ‘Tricolor’ seedlings with the first expanded true leaf were grown under three shading levels (20%, 50%, and 77%, ca. 859, 567, and 258 μmol•m-2•s-1 averaged noon time PPF) with four Johnson’s solution (J) strength (0%, 50%, 100%, and 200%). When supplied with 100% J, plants grown under 77% shading had lower light compensation point (LCP), light saturation point (LSP), light saturated photosynthesis rate (Amax), and dark respiration (Rd). Plants supplied with 200% J under 20% shading, had the highest whole plant net photosynthesis, LCP, LSP, Amax, and Rd, shoot and root dry weights, leaf number, leaf area, and SPAD-502 value. Seedlings were stunt when supplied with tap water only. Neoregelia ‘Pink Sensation’ × ‘Tricolor’ seedlings with the first expanded true leaf were supplied with various nitrogen (N) concentrations weekly. Results showed LSP and Amax increased with increasing N from 0 to 20-28 mM. Light compensation point did not differ between treatments. Shoot and root dry weights, leaf number, leaf area, and SPAD-502 value increased as N concentration increased from 0 to 20-24 mM, and saturated thereafter. Plant C and N concentration increased with increasing solution N concentration. Plant K and P concentration did not differ between solution N concentration treatments. Plant Ca concentration increased when solution N concentration increased from 0 to 8 mM, but decreased as solution N increased from 12 to 32 mM. Plant Mg concentration decreased with increasing solution N concentration. Neoregelia ‘Pink Sensation’ × ‘Tricolor’ seedlings with the first expanded true leaf were supplied with 0 : 100, 25 : 75, 50 : 50, 75 : 25, and 100 : 0 NH4+ : NO3- weekly. Result showed plants had the heighest Amax and lowest LCP when supplied with 25 : 75 and 50 : 50 NH4+ : NO3-. Plants had the heighest shoot and dry weights, leaf length, leaf width, leaf number, leaf area and plant C concentration but lowest plant N concentration when supplied with 25 : 75 NH4+ : NO3-. Plant P and K concentration were lowest when supplied with 0 : 100, 50 : 50, 100 : 0 NH4+ : NO3-. Solution nitrogen form did not alter plant Ca and Mg concentrations. Neoregelia ‘Pink Sensation’ × ‘Tricolor’ seedlings with the first expanded true leaf were supplied with 0, 2, 4, 6, 8, 10 mM K. Result showed plants at 0-2 mM K had higher LCP, LSD, and Rd than those at 4-10 mM K. Amax increased with increasing K concentration from 0 to 8 mM, but decreased with further increased K concentration to 10 mM. Shoot and dry weights, leaf number, leaf length, leaf width, and thickness increased, but SPAD-502 decreased, when K concentration increased from 0 to 6-8 mM. Plant C and N concentration decreased with increasing solution K concentration. Plant P concentration increased with increasing solution K concentration from 0 to 4-6 mM, but decreased when solution K concentration further increased. Plant K concentration increased with increasing solution K concentration. Solution K concentration did not alter plant Ca and Mg concentration.