The effect of soil inoculants on seed germination of native and invasive species

Successful reintroduction of native species through ecological restoration requires understanding the complex process of seed germination. Soil microbes play an important role in promoting native establishment and are often added to restoration sites during seed sowing. We tested the role of soil-and lab-grown bacterial inoculants on germination timing and percent germination for 19 species of plants commonly found in coastal California. Each species exhibited a different response to the inoculant treatments, but overall time-to-germination was longer and percent germination was lower with the soil inoculant compared with the control or other treatments. The invasive species in our study had the highest percent germination of all species and germinated faster than all native shrubs. Germination timing was negatively correlated with percent germination and with seed mass. Our results suggest that lab-grown inoculant and chemical treatment are effective at increasing germination in some native species, whereas soil inoculant is not. Given differences in germination timing between native and invasive species, restoration practitioners could consider using herbicide to treat areas seeded with native shrubs immediately following germination of invasive species without harming most natives, although germination timing and herbicides need further study in relation to microbial effects on seed germination.