Picture of the inside of one of the three semi-open greenhouses of 72 m² for conducting CO2 experiments in mangroves trees in New Caledonia. Inside each greenhouse, a circular closed chamber of 36 m² (2.4 m height) is built to maintain elevated atmospheric CO2 concentrations controlled by CO2 probes connected to a central unit. Pure CO2 gas is supplied from 5:00 am to 7:00 pm at the top of the chambers by brief pulses from a high-pressure cylinder. Mangrove seedlings Avicennia marina and Rhizophora stylosa are placed on custom-build tidal tables, each working individually. Each tidal table includes a 700-liters polypropylene tank (1 m² area over 0.7 m height), surmounted by a 300-liters planting tray (1 m² area over 0.3 m height). Fresh seawater is pumped from the adjacent lagoon (20 m) and stored in the tanks, replaced twice a month. To simulate high tide periods, an aquarium pump, placed in each tank, sends the water to the planting tray. A siphon pipe allows the planting tray to completely drain the water back to the reserve to reproduce low tide periods. To control the tidal treatment attributed to each tank, the aquarium pumps are connected to three custom-build current controllers (one per greenhouse). Controllers are constructed from Arduino open source plans available for free under public licenses and are programmed according to the needs of the experiment.