Arbuscular mycorrhizal fungi (AMF) are important plant mutualists that can facilitate plant responses to various environmental stressors, such as drought. A plant that may benefit from AMF-induced drought tolerance is Conyza canadensis due to its ability to thrive in dry conditions and its high colonization rate. However, no studies have researched C. canadensis in this context and the exact mechanisms of AMF-induced drought tolerance are still unknown. To better understand if and how AMF facilitate drought response in C. canadensis, we conducted a greenhouse experiment comparing the response of mycorrhizal and non-mycorrhizal plants to three watering levels. We measured dry biomass, water content, leaf water potential, photosynthetic rate (Pn), stomatal conductance, and shoot N and P concentrations. AMF improved plant performance under drought, and the magnitude of that improvement was modulated by the severity of drought imposed. We showed that AMF upregulate stomatal conductance, photosynthesis, and increase P uptake. In conclusion, we find that AMF protect Conyza from the most severe drought stress, and that this response is likely mediated by increased stomatal control and nutrient uptake. Colonization led to biomass reductions, which suggests AMF benefit C. canadensis more in the way of drought tolerance and nutrient uptake, rather than improving growth
