Effects of duckweed (Lemna minor) biomass on epiphytic diatom colonization under aeration disturbance

Diatoms (Bacillariophyta) have important biological significance and application value. Diatoms are important primary producers in water bodies and can serve as bait for many fish, shellfish, and other aquatic animals, thus playing a crucial role in aquatic ecosystems, particularly in aquaculture. The high-density cultivation of diatoms, particularly epiphytic species, represents a critical research frontier in aquaculture. However, there is currently limited research on using natural aquatic plants to cultivate epiphytic diatoms. In order to cultivate epiphytic diatoms with Lemna minor, a culture experiment was conducted with decaying L. minor in different biomass under aeration disturbance. According to the wet biomass gradient of the rotting L. minor, a total of 5 treatments were set as 0, 4, 8, 12 and 14 g/L, named as treatment Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅴ from low to high, respectively, each with 3 replicates. The results showed that no hypoxia occurred in any of the treatments. The concentrations of ammonia nitrogen (NH₄⁺-N) and soluble reactive phosphorus (SRP) in treatment Ⅰ (0.584±0.649) and (0.336±0.274) mg/L, respectively were significantly higher than those in the other treatments (P<0.05). The dissolved total nitrogen (DTN) and dissolved total phosphorus (DTP) concentrations in all treatments exhibited a declining trend before stabilizing, with no significant differences observed between treatments. Although treatment V had the highest mean DTN (1.665±1.678) mg/L and DTP (0.603±0.672) mg/L concentrations, these values were not statistically significant. In the middle and late stages of the experiment, diatoms of Navicula and Cocconeis appeared on the rotting L. minor, and the wet weight of the epiphytic diatoms of treatment Ⅳ was the highest (P<0.05), reaching the maximum of 249.13 mg/L on the 35th day. The maximum biomass of epiphytic diatoms on L. minor was significantly higher than that on glass sheetS (P<0.05). The results show that the wet biomass of rotting L. minor at 12 g/L is more conducive to the growth of epiphytic diatoms under aeration disturbance, and L. minor are more beneficial to the growth of epiphytic diatoms than glass sheet. The rotting L. minor releases nutrients such as nitrogen and phosphorus, providing a material basis for the growth of diatoms and serving as a medium for the diatoms’ attachment growth. This experiment provides a feasible method for cultivating epiphytic diatoms in a decaying state of L. minor under aeration disturbance, expanding the cultivation method of epiphytic diatoms.