You can read the abstract of this publication. The rest of the article is in ukranian... But it's quite recent. Perhaps, you can contact the authors to get the figures explanation in english : http://ojs.mdpu.org.ua/index.php/biol/article/view/2/1725
Although your question requires a deep explanation on a biochemical basis, I dare to tell you that this factor should positively impact on major soil microbiota since energy rich crops usually are rich in carbohydrates, which is a source of carbon for bacteria. But notice that this is just a response at glance, only a quick chat opinion. I recommend you to contact colleagues with expertise on green manures.