AimsPlants, fungal endophytes (FEs) and the changing environment interact with each other forming an interlaced network. This study evaluates nonadditive and interactive effects of the FE Acremonium strictum and drought treatment on Atractylodes lancea plantlets. Methods and ResultsBy applying FEs (meristem cultures of At.lancea, fungal inoculation of Ac.strictum and plantlet acclimatization) and drought treatment (regular watering, mild drought, severe drought), a research system of At.lancea ramets under different treatments was established. During 12days of drought treatment, the plantlets' physiological responses and basic growth traits were measured and analysed. Although drought and FE presence affected plantlet traits to differing degrees, the interactive effects of the two were more pronounced. In particular under mild drought treatment, the FE conferred drought tolerance to plantlets by enhancing leaf soluble sugars, proteins, proline and antioxidant enzyme activity; decreasing the degree of plasmalemma oxidation; and increasing the host's abscisic acid level and root:shoot ratio. When exposed to regular watering or severe drought, these effects were not significant. ConclusionsPlant traits plasticity was conferred by dual effects of drought stress and FEs, and these factors are interactive. Although FEs can help plants cope with drought stress, the beneficial effects are strictly constrained by drought degree. Significance and Impact of the StudyDuring finite environmental stress, FEs can benefit plants, and for this reason, they may alleviate the effects of climate change on plants. However, because the benefits of FEs are highly context dependent, the role of FEs in a changing background should be re-assessed.