Ecological interactions among microbial functional guilds in the plant-soil system and implications for ecosystem function

BackgroundSoils harbour a remarkable diversity of interacting fungi, bacteria, and other microbes: together these perform a wide variety of ecological roles from nutrient cycling and organic matter breakdown, to pathogenic and symbiotic interactions with plants. Many studies demonstrate the role of microbes in plant-soil feedbacks and their interactions with plants. However, interactions among microbes are seldom addressed, and there is no consensus regarding the nature and outcomes of interactions among microbial functional guilds.ScopeHere, we critically review what is known about microbe-microbe interactions among functional guilds within the plant-soil system, with the aim to initiate a path to disentangling the “microbe black-box”. Our review confirms that the nature of microbial interactions among major functional guilds is explained by niche theory. This means that, among microbes, a competitive relationship is likely when their benefits to plants, source of carbon and nutrients, or nutrient scavenging mechanisms overlap, while a neutral-to-facilitative relationship is likely when these microbial traits differ or complement each other.ConclusionsWe highlight the numerous knowledge gaps and provide a framework to characterise microbe-microbe interactions that offers insight into the contributions of microbes to key ecosystem functions such as carbon sequestration and nutrient cycling.