Priority effects of inoculation timing of plant growth-promoting microbial inoculants: role, mechanisms and perspectives

BackgroundPlant growth-promoting microorganisms (PGPMs) have been extensively used in agricultural and environmental management strategies to improve plant growth, nutrient absorption and resilience to environmental stress. To ensure the successful establishment and competitive advantage of PGPM inoculants against other source pool microbes, seeds, seedlings and soil are commonly pre-treated with microbial suspensions. The preferential colonization of PGPMs triggers a series of plant-microbe feedback responses via modulating plant root exudates, ultimately affecting the composition and function of the root microbiome. This phenomenon, called priority effects, has profound and long-lasting implications in shaping the assembly and stability of the root-associated microbiome. However, harnessing these priority effects to engineer or manipulate microbiomes remains an area that requires further exploration.ScopeIn this article, we review the priority effects and underlying mechanisms governing the timing of inoculation of PGPM inoculants. We delve into the intricate interactions between PGPM inoculants and root-associated microorganisms, examining both their direct interactions and those mediated indirectly via the modulation of plant root exudates. This exploration aims to uncover the priority effects of PGPM inoculation on the root microbiome and its associated functions.ConclusionsWe offer insights into the potential applications and further prospects of PGPMs in agricultural and environmental management practices, with a particular focus on their priority effects. This perspective aims to foster a deeper understanding of the role of PGPMs in microbiome engineering and plant health promotion.