Interesting. But it is understood that at least in some soils, compost application significantly increases macroaggregation. See Table 1 in this reference, and elsewhere. It would seem that in Kentucky silty loam, it might not.

I accept that fungi is mainly responsible for this macroaggregation, but compost is probably responsible for encouraging the fungi.

nice paper Dan. But it is about a rice field in Japan. I work there a month to two months a year, and know them well as they are along my bike commute. those fields are under water six months a year. So the wet six months there are no fungi. Perhaps a special case? Off topic, but they keep them smooth as a pool table, which they must if they are to keep everything under water in 2 inches.

Agreed, that the circumstances probably depend a lot on the type of soil. But I suspect that the organics in compost do encourage fungal growth. That is, the compost itself doesn't provide microaggregation, but maybe under the right conditions it helps something that does.

Actually, isn't it clear that the compost degradation process is partly fungal?

It is good to summarize the ways in which bacteria save a plant's energy, which can be re-directed towards growth and production (which is what we care about here).

- they fix N in the soil, of course.

- they largely transport organic N from bulk soil to the rhizosphere, where the plant puts out sugars for their consumption. They are very green as a material (C/N of 5 to 9), and this transport allows the plant to work with puny roots. A typical plant roots will access only 2% of the soil in the volume defined by its dripline circle times its height. No need to access more, and therefore spend energies on root development, if nutrients are carried to you.

- that N is in amino-acid form, which are absorbed directly, saving the plant the work to re-assemble the amino-acid from elemental N. Granted the aminos are in the form of bacterial predators feces, deposited right there. I speculate that the protozoa also want sugars, so that N is further concentrated in their feces.

- they save the plant substantial defense energy, when the bacterial mix is right.

Arbuscular myc. also do defense by covering roots and P and water transport. They also do pre-filtering of bad things such as aluminum ad cadmium, so that the plant nutrients absorbed through them are less contaminated. Relative importance of these creatures for plant development depends on which one is the limiting factor for growth.