For the CO2 gradient cultures, CO2 concentrations (pCO2)were automatically controlled at 390μLL−1 (current ambient CO2concentration,AC) and 1000μLL−1 (elevated CO2, EC) in two incubators. In each incubator, the two species were cultured using both methods: monoculture (M) and biculture (B). For monoculture, 4 g of each species (fresh weight, Fw) was separately cultured in two 5-L flask tanks; for biculture, 2 g of each species (Fw) was placed in one 5-L flask tank(a total Fw of 4 g in one flash tank). Three replicates were prepared for each treatment