I'm not at all certain on this, but I think leaves are generally considered low-nitrogen in terms of composting. I forget how the whole deciduous leaves things work, but isn't most of the nitrogen in leaves involved in chlorophyll? -Is the process of leaves changing colour the chlorophyll (and other phytopigments) the plant reabsorbing the nutrients, or is it just breaking down/wearing out?.
Anyways, I could possibly see that some microbes would set up camp on the leaves, using the carbon in cellulose, lignin, and what not, but be somewhat nitrogen starved.
I'd also be interested in reading a summary of that paper/the article itself if you happen across it again.