Talking about these two changes, well, mainly the second one. The first one is manageable.
> Arcane Smash (Q) mana cost increased from 45 to 45/50/55/60/65.
> Sapling Toss (E) - [removed] no longer deals 40/60/80/100/120 (+40% AP) damage on landing impact.
AP Maokai wasn't weak per say, but not nearly strong enough to warrant the same nerfs as tank Maokai. How about a small compensation buff such as a slight increase on the AP-scaling on the explosion or one of his other abilities? The only historically strong AP item on tank Maokai (that I can think of) is Rod of Ages, which delays his early power spike anyways.
If that isn't preferred, another small thing could be a shorter cooldown on the sapling toss (once again, just a small buff needed). Top+tank Maokai won't use it to murder everything (Q+W+R are better in teamfights anyways) and it won't make or break laning phase. On AP Maokai it's a big thing though and as a bonus it might help a bit with jungle Maokai which could help at least one of the few tank junglers out there.