Optimization of Hoagland Nutrient Medium and Controlled Clonal Propagation of Lemna Gibba L. in Fishpond Wastewater: from Laboratory Acclimatization to Field Biomass

Nutrient-rich wastewater discharged from fishponds constitutes a source of ecological load and, at the same time, a secondary nutrient resource for fast-growing floating macrophytes. The aim of this study was to determine the effective Hoagland concentration for Lemna gibba L., to acclimatize the plant stepwise to fishpond wastewater, and to evaluate the feasibility of controlled clonal propagation under field conditions without supplementary mineral fertilization. Initially, the morphometric parameters of an inoculum of 5.0 g fresh biomass were standardized (n=5). Eleven variants of modified Hoagland medium within the 0×–1.0× range were tested in a 10-day preliminary screening; the 0.1×, 0.3× and 0.4× variants were selected for subsequent validation (n=3). The highest performance was observed in the 0.1× medium, in which biomass reached 69.97±0.51 g, surface coverage 702.3±3.57 cm² and RGR 0.264±0.001 day⁻¹ on day 10. Thereafter, three parallel clonal lines were sequentially transferred to 25, 50, 75 and 100% fishpond wastewater. As the wastewater proportion increased, day-10 biomass rose from 70.05±0.38 g to 77.88±0.28 g, and RGR from 0.26398±0.00054 to 0.27458±0.00035 day⁻¹. When the culture acclimatized to 100% wastewater was tested in three field units of 0.49 m² each, biomass amounted to 81.70±0.20 g, RGR to 0.27936±0.00024 day⁻¹ and net fresh biomass productivity to 15.65±0.04 g FW·m⁻²·day⁻¹. Drying 50.0 g of fresh biomass at 50°C for 6 h yielded 5.97±0.18 g of dried mass. The results demonstrate that stable clonal biomass of L. gibba can be produced by stepwise transfer from an optimized initial mineral medium to 100% fishpond wastewater.