I pickled sweet potatoes once. It wasn't for me, it was baby food.

There is a dish called "poi" which is pickled taro root.

Carrots are incredibly delicious when pickled.

Carrots and radish are common ingredients in kimchi.

Whenever I'm getting a cold, I crave fermented carrot juice with ginger.

Pickled mustard root is a traditional Szechuan ingredient.

Don't forget pickled beets! You can make a fermented drink with beets called beet kvass.

And of course all root beers - birch, ginger, sassafras, sarsparilla etc. Not pickled in the brine sense, but definitely fermented by tradition.

Fermentation transforms carbs into lactic acid and/or alcohol, so it reduces the amount of carbs. I don't know by how much, though.