> That leads to 0.05 J of extra energy per gram of microbial bio material

Over what timeframe? If that’s 0.05 J per hour and “the researchers found that fungi that faced the galactic cosmic radiation for 26 days grew an average 1.21 times faster” 26 * 25 / 21% and the numbers don’t look that unreasonable.

I calculated over 5 days. Which was just a guess.

But i focused on the 10% mentioned.

That said time could be factored out if you did everything properly.