Objective  Optimal conditions for the growth of Leucaena leucocephala seedlings in an indoor facility were studied.

  Methods  Selected morphological and physiological indices of L. leucocephala seedlings were monitored for the optimization in a chamber under varied light exposures (i.e., 12, 16, 20, and 24 h·d⁻¹) with the intensity of 100, 200, 300, or 400 μmol·m⁻²·s⁻¹ in a nutrient solution of a salinity of 7‰, 15‰, 20‰, or 25‰, a N concentration of 7.5, 15, 30, or 60 mmol·L⁻¹, and a P concentration of 0.5, 1, 2, or 4 mmol·L⁻¹.

  Results  The single factor experiment showed the seedling morphological indices increased at first and then decreased with increasing light exposure, light intensity, N or P concentration. After 35 d of cultivation, the average fresh weight of an individual seedling exposed to 20 h·d⁻¹ of light reached (5.61±0.11) g, which was 60.0% higher than that exposed to 12 h·d⁻¹ or 14.6% higher than that exposed to 24 h·d⁻¹. The intensity of light at 200 μmol·m⁻²·s⁻¹ resulted in a (6.55±0.10) g·plant⁻¹ of fresh seedling, which was 21.5% or 62.1% higher than at 100 μmol·m⁻²·s⁻¹ or 400 μmol·m⁻²·s⁻¹, respectively. The nutrient solution containing 15 mmol·L⁻¹ N yielded a fresh seedling weight of (4.32±0.10) g·plant⁻¹, which was 6.1% and 108.6% higher than those at 7.5 and 60 mmol·L⁻¹, respectively, in concentration. Whereas P at 1 mmol·L⁻¹, the fresh seedling weight was (5.65±0.21) g·plant⁻¹, which was 40.9% and 64.7% higher than P at 0.5 mmol·L⁻¹ and 4 mmol·L⁻¹, respectively. And the seedlings exhibited similar patterns under those conditions on chlorophyll content, chlorophyll fluorescence parameters, and antioxidant enzyme activities. On the other hand, the seedlings growing under an increasing salinity displayed decreasing trends on the morphological indices, chlorophyll content, chlorophyll fluorescence parameters, and antioxidant enzyme activities. At 7‰ salinity, the greatest fresh seedling weight of (8.95±0.05) g·plant⁻¹, dry weight of (2.16±0.16) g·plant⁻¹, plant height of (31.17±1.67) cm, root length of (60.67±0.93) cm, and total chlorophyll content of (1.72±0.06) mg·g⁻¹ were recorded. In contrast, the chlorophyll fluorescence parameters and antioxidant enzyme activities were improved.

  Conclusion   Under 20 h·d⁻¹ of 200 μmol·m⁻²·s⁻¹ light exposure, the growth of L. leucocephala seedlings in a nutrient solution of 7‰ salinity that contained 15 mmol·L⁻¹ N and 1 mmol·L⁻¹ P rendered the morphological indices, antioxidant enzyme activities, and chlorophyll fluorescence parameters superior to the other tested conditions in a nursery.