The sterilized living N. minor (100 g) was cultured for 7 days in a beaker containing 2 L Hoagland medium (0.1×) as described pre- viously [15]. The beakers were covered by sterilized filter paper and then placed in an incubator using light intensity of 120 μmol m−2 s−1 at 25 ± 1 °C and photoperiod 14L:10D [5]. Then the culture solu- tion (containing exudates of N. minor) was collected and concentrated to 200 mL by rotary evaporation, and filtered with Millipore glass filter (0.22 μm pore size). The cultured N. minor was also collected for latter coexistence experiments.