Dear Shi Xuan, firstly: welcome here. We are always happy about newcomers to the forum, but especially those who obviously have much knowledge and experience or ask very interesting questions.
Your topic is extremey interesting and I am not able to respond in exact a manner. I think nobody has investigated in the decaying processes intensely enough to differentiate the microorganisms in precise a way. But what I can say is that you are probably right in presuming that they are different from those which take part in the normal cycling processes in a well-functioning tank. The experience of experienced aquarists leads to that conclusion. But we don’t know which organisms are playing which role in this.
With Paro-aquaristics this is partly the same as in normal aquaristics, and partly it is not because of the different water values. The situation in a blackwater tank with very low pH and very low Microsiemens maybe rather different from that in a normal tank with barbs or cichlids. Presumably, the risk is higher that the change I mention below happens faster and with more serious consequences for the milieu of the tank. Blackwater aquaristics surely is possible but we know less about it than about the normal, ordinary aquarium.
Most Paro-specialists are eager to remove decaying leaves after a certain amount of time since we have often seen maladies and indications of illness in our fish when too Long exposed to that conditions. Catappia leaves fro instance should not remain in the tank until they are completely rotten; the healthy environment they can create changes into the opposite after about four or six weeks. Then they should be exchanged at the latest against new ones.
But I must admit that I often do not follow my own insights myself. That’s a problem.
So, I do not know of any scientific articles which inform us about what exactly happens here. I should be happy to know if somebody knows things better.