Why is my Riccia fluitans dying?

[mackeith]

i been having this riccia in my planted tank for a few months and it has grown 3 x times its original amount. seeing that, i removed it from its original stone which it was tied to and spread it over a new driftwood and place back into the tank. however, things start to go wrong and the riccia starts turning pale now now brown..... most of my other plants and moss are ok just the riccia. is it because of the wood?