Can we condition native plants to increase drought tolerance and improve restoration success?

A common method in ecological restoration is the transplanting of nursery-grown seedlings to the field and, with proper resources, this technique can be highly successful. However, stressors such as drought may negatively impact plant performance and restoration success, especially in dryland ecosystems. Furthermore, increasing environmental change may hamper the ability of practitioners to restore native vegetation. A growing body of research suggests that exposing plants to a stressor may improve tolerance to subsequent stress events later in life. We sought to understand if such a phenomenon could be exploited in order to improve plant drought-tolerance and aid native plant restoration in southern California. In a multi-phase experiment, we first exposed seedlings of native perennials to episodic drought and then later compared the response of these plants to a second drought event to that of well-watered controls. We also transplanted replicates of both treatments to a restoration site in the field to test whether exposure to drought as a seedling could improve plant performance. Plant species responded to drought differently, with species exhibiting the full range of positive, neutral, and negative responses to temporal variability in water stress. However, some species appeared to benefit from drought preconditioning, exhibiting greater growth and increased water-use efficiency compared to well-watered plants. This suggests that simple applications of stress treatments could improve plant growth and stress tolerance, but the success of this method is likely very species specific. Restoration practitioners should consider conducting pilot studies with target plant species to better understand if this technique could assist in achieving restoration goals.