Stephanie S. Porter, Roxanne Bantay, Kathleen Ibarreta, Colleen A Friel, Aaron Garoutte, Kristi Gdanetz, Bethany M. Moore, Prateek Shetty, Eleanor Siler, Maren L. Friesen
Extreme conditions such as drought, heat, salinity and cold, and outbreaks of insect pests and disease are becoming more common in many areas due to global change. Plants’ ability to tolerate such environmental stresses is impacted by the plant microbiome: the bacteria and fungi that live on or inside of plants. However, scientists usually study the impacts of beneficial microbes and environmental stresses on plant performance in separate experiments. Our research is novel because we compare the roles of different types of beneficial microbes in protecting plants from different environmental stresses, such as pathogens, herbivores, drought and salinity. We examine trends across data from 288 experiments from 89 previous studies. We find that microbial partners have a greater proportional impact on plant performance in more stressful environments. Therefore, symbiotic microbes protect plants from environmental stresses. Our results show that environmental conditions affect the degree to which beneficial and harmful microbes in the plant microbiome impact plant health. Different microbes offer different amounts of benefits to plants, and the amount of benefit they provide differs between high and low stress environments. In non-stressful conditions, beneficial symbiotic bacteria confer greater benefits to plants than do symbiotic fungi. However, under stressful conditions, symbiotic fungi, especially the mycorrhizal fungi that grow on plant roots, confer greater benefits to plants than do bacteria. Overall, we find that beneficial microbes reduce plant stress in response to salinity, insect damage to leaves, and fungal disease. Beneficial symbiotic microbes are especially important for plant health in stressful environments and could help to reduce the negative consequences of global change for plants.