Effects of light source and photoperiod on growth of duckweed Landoltia punctata and its water quality

Abstract

This study investigated the effects of light source [LED white (LW), fluorescent white (T5) and LED blue (LB)] and photoperiod (12:12, 16:08, 24:00 light/dark) on growth of duckweed Landoltia punctata and the resulting effects on its water quality for 16 days. The average daily relative growth rate (RGR) reached about 0.519 g d−1. Both light source and photoperiod had no significant difference on the mean RGR; however, their interaction had significant effects on duckweed's growth (p ≤ 0.05). Moreover, except T5 (24:00) > [T5 (12:12) ≥ T5 (16:08) ≥ LB (24:00)], LW (12:12) > [T5 (16:08) ≥ LB (24:00)], and LB (12:12) > LB (24:00), there were no differences in RGR in all pair-comparisons of treatment (p ≤ 0.05). Nitrate (NO3−) mostly influenced weight increment (WI), 70%. For light source and photoperiod effects on water quality, no total ammonia nitrogen (TAN) was detected in all treatments after 16 days, while NO3− increased gradually. In addition, results show that most of the total nitrogen (TN) was contributed from NO3− (R2 = 0.9999). Overall, our findings could contribute on producing duckweed in a controlled and programmed condition for maximum production and quality. Constructed models and practical application contribute in predicting nutrients sensitivity and proven useful in water management or water quality assessments.