Independent and differential effects of arbuscular mycorrhizal fungal composition and plant pathogens on plant traits and nitrogen uptake

Arbuscular mycorrhizal fungi (AMF), as microbial mutualists, interact with
various microbial taxa, including pathogens, and significantly shape the
ecology and evolution of their host species. However, how AMF and
pathogens jointly or independently affect plant traits and nitrogen uptake
remains unclear. Here we conducted a factorial experiment with three AMF
treatments (AMF-free-control, Funneliformis mosseae, and a mixture of AMF
species of F. mosseae and Claroideoglomus etunicatum), four plant-pathogen
pairs, each under two pathogen treatments (one pathogen and a
pathogen-free control). After 65 days of growth, we measured AMF
colonization, pathogen infection, plant functional traits, and ammonium
and nitrate uptake. Our findings reveal that AMF and pathogens
independently influence plant traits and nitrogen uptake, with no observed
interactions between them. Specifically, colonization by F. mosseae or a
mixed AMF species reduced nitrate uptake and plant height, without
affecting root traits or ammonium uptake. In contrast, pathogen infection
enhanced acquisitive root traits, such as increased specific root length
and area, but did not impact shoot traits or nitrogen uptake. These
results broaden our understanding of the tripartite interactions among
plants, AMF, and pathogens, offering insights into how plant-microbial
relationships influence plant health, growth, and nitrogen cycling.