I'm trying to grow Japanese Maples from Seeds. I had over 100 germinate this year and now I think they're all dead. One the seedling reaches an inch plus, it puts out true Japanese maple leaves. After a few days to a week, they all shrivel up. The stem of the seedlings have remained erect after the death of the leaves, could they come back? What am I doing wrong. Any help would be greatly appreciated. Also my Sugar Maple seedlings and oak seedling with 8+ leaves on them also slowly dry out and eventually fall off. What could be going on? I've been moving them to much larger pots once their roots begin to develop, before they get overcrowded.
First, Japanese Acers do not form a taproot, so the depth of the cell, at 2 inches, shouldn't be too much of a problem. However, you say in a comment that you move them outside 'for sunlight'. This is not a good idea - seedlings, unless they germinate outdoors and are immediately exposed to an open environment, need acclimatizing to conditions outdoors, and it's not a good idea to stand them in direct sunlight suddenly. When you do move them outdoors, make sure they are not in direct sunlight for the first couple of weeks, though dappled sunlight early or late in the day is fine.
The ones that now have no leaves are unlikely to grow, but you can leave them for a while and keep your fingers crossed if you want to give them more time. Since Acer palmatum (japanese acer) does not come true from seed, it will be interesting to see what characteristics those seedlings you have left develop over time.
Tap water or soil may be the problem, it maybe slightly salty for small Japanese seedlings. it will slow down the growth or may kill it. Fertilizer is not necessary for seedlings until 2nd or 3rd year and will kill it as well when roots are versensitive first a few months.Try to save rain water or use filter water for watering until they become large. I have grown some from seed and a few of mine died but i figure out what problem was so they are recovering now.