2.1. Hydroponic setup

Hydroponics was used in order to limit the effect of organisms found in soils. The hydroponic solutions used in this study were made by adding 5 mL of liquid fertilizer (Simple Nutrient Addition Program - SNAP) to 3 L of distilled water. The addition of liquid fertilizer is needed for the growth of plants in hydroponic systems in the absence of liquid circulation [20]. CuSO₄•5H₂O and NaOH crystals were then added in order to simulate increased copper concentrations at varying pH. Each of these hydroponic solutions housed one six-month-old D. asper propagule. Although there was no written record on the exact date when each of the propagules germinated, it was assured that they were of the same age based on the height, number of leaves as well as nodes formed (morphological parameters used by the growers).The SNAP solution was bought from the Soil Science Department of the University of the Philippines Los Baños (UPLB) while the propagules were sourced from the Department of Environmental and Natural Resources - Ecosystems Research and Development Bureau (DENR - ERDB) in Los Baños, Laguna, Philippines.

Each hydroponic jar of 23.5 cm diameter contained 3-L of hydroponic solution. This liquid level started at around 7 cm, but throughout the testing period, the liquid volume of these hydroponic jars decreased by around 75 mL/day.