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

Abstract

Successful re-introduction 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 nineteen species of plants commonly found in coastal California. Each species exhibited a different response to inoculant treatments, but overall time-to-germination was longer and percent germination was lower with soil inoculant compared to 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 weight. Our results suggest that lab grown inoculant and chemical treatment are effective at increasing germination in some native species, while 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.

Restoring a Mediterranean‐climate shrub community with perennial species reduces future invasion

“…Perennials may be able to create a more invasion resistant community relative to native annuals, because if they survive the summer dry season they can compete for space, light, and water with non‐native seedlings from the first rain rather than waiting for specific germination cues. In contrast, annual species must germinate each year, and germinate later than the invasive species, putting them at a phenological disadvantage in competing for resources (Wainwright et al ; Balshor et al ).…”

“…Native seedlings emerged in the field at higher densities than were used in the pots, so the strength of competition may have been even greater between native functional groups. Also, the native annuals germinate earlier than the native perennials, putting them at a phenological advantage during initial establishment (Balshor et al ). As expected, B. nigra was a stronger competitor with the natives than natives were with themselves.…”

“…In this system, an area initially dominated by invasive grasses often give way to the invasive forb Brassica nigra , which is also a strong competitor with native annuals. The competitive strengths of B. nigra are early phenology, rapid growth rate, and high seed production (Roberts ; Balshor et al ). The early phenology can also allow managers to strategically remove this species prior to native germination to facilitate native species growth.…”

Resistance and resilience: ten years of monitoring shrub and prairie communities in Orange County, CA, USA

“…, Balshor et al. ). However, the non‐native forb Brassica nigra also had highest cover in wet years preceded by dry years according to our multiple regression, indicating the ability of non‐native forbs to increase when released from competition by non‐native grasses (Cox and Allen ).…”

“…, Balshor et al. ). Following invasion, it may be difficult for the community to return to a diverse native‐dominated community without intervention in the form of ecological restoration (Suding et al.…”