This developing dawn redwood was kept in a tub of water throughout the season. It put on about 4’ of top growth. No problems.
(Don't let the skimpy appearance fool you, that’s residual inner growth following a massive haircut).
The tree is planted in pumice with a bit of df bark in an Anderson flat. Water level submerged 1/4 to 3/4 the height of the flat most of the time.
Root growth was very strong. Numerous tentacles extend through the water.
The high water table appears to have prevented fine roots at the soil surface from drying out.
In my case, the only notable downside to growing the tree this way appears to be the mosquito larvae that also grew in the tub.