Originally Posted by echinosum

In moving the clump of bamboo, you have inevitably damaged the roots, and almost certainly not taken all the roots with you - many of them are very fine and extending a long way, as well as the thick rhizomes. It's the fine roots that gather water and nutrients, so their loss is keenly felt by the plant.

So you now have a plant that doesn't have all the roots it used to have, and is putting energy into repairing and extending its root system. So it no longer has sufficient energy/resources to support all of the above-ground part of the plant. Which is why it is shedding leaves.

What you need to do in this situation is reduce the size of the above-ground part of plant. People have various theories on the best way to do this, some shorten the canes, some selectively cut out some of the canes, some partially de-leaf the plant. Since you already have some damage, I think you should take out any parts of the plant that are damaged. And then use your judgment how to reduce further if necessary. People usually say you should reduce the plant by about 30-40%, ie a third or a bit more.

You also need to feed and water it well. The plant should then re-establish itself, and send up new canes in future years, so you'll probably regain its previous look, if not next year, then in two or three year's time.