Microbial–Faunal Interactions in the Rhizosphere

Soils are home for a huge variety of organisms that are profoundly enriched in the rhizosphere. The most abundant ones, microbial bacteria (and to a lesser extent archaea) and fungi, directly compete for plant-derived nutrients that they use for reproduction. Predators of these minute microorganisms control their abundances, community structure and activity. Microbial protists, faunal nematodes and microarthropods are arguably the main bacterial and fungal predators, but also other groups including enchytraeids and even predatory bacteria, fungi and viruses contribute to microbial mortality. In this chapter, we introduce the major predators of microorganisms, their specific interactions with bacteria and fungi, and how predation on microorganisms affects nutrient cycling and eventually plant performance. We focus on protists and nematodes as the key microbial predators. We exemplify how this knowledge helps at better understanding microbial–faunal interactions, and how interactions among those microbial predators affect soil food webs. Overall, we show that the diversity of microbial predators is key to control rhizosphere microbiomes and, eventually, governs plant performance.