The Soil Food Web: Fungi, Bacteria, Worms and Bugs

Healthy soils are literally teeming with life. Mycorrhizal fungi establish symbiotic relatiobnships with plant roots, producing fungal threads called “hyphae” that form an interconnecting network into the soil – looking for sugars and complex molecules in return for nourishing the vine. These fungi also provide the substrate for bacteria which grow around the hyphae, taking up nutrients and converting them into a form that the fungi can use. Then you’ve got the arthropods and worms that travel through the soil, moving nutrients into the root zone, eating plant matter, producing nitrogen, and providing water channels and pores for the roots to penetrate. Studies have shown that plants growing in phosphorus-poor soils that nevertheless contained mycorrhizal fungi did better than plants in soils with normal phosphorus levels but no fungi. We think that part of the reason is that fungi are responsible for many aspects of soil health. First, they produce organic acids, which help maintain soil pH levels in the slightly acidic range (5.0-7.0). This is important because when healthy soils are slightly acidic, it keeps nitrifying bacteria – which convert ammonium to nitrite and then nitrate – down, so that the majority of the nitrogen in fungi-rich soil is present as ammonium, not nitrate. Vines are much more efficient at using ammonium than nitrate. Second, the fungi act as a food source to soil-borne arthropods and nematodes. These fungal-eaters also release nitrogen in the form of ammonium, which the vines can more effectively use.

So there’s a lot going on below the surface. I like to think that one should spend as much time thinking (and worrying) about what’s going on underneath the soil as above it. Maybe even more so.