I would have thought that the fact that the experiments with leaves brought there from elsewhere decaying slower demonstrate that merely bringing foreign organisms (the collected leaves are not sterile, of course) is not going to help.
The collected leaves are not sterile, but that isn't where the bulk of the organizes live. They live in the soil.
The best thing to do is leave it alone and let organisms that are tolerant of radiation evolve.
Perhaps we have a solution to carbon sequestration!. (I kid of course).