Increasing rates of vegetation clearing are occurring throughout Australia with rates of clearing in New South Wales tripled over the last decade (EPA, 2021), thus the need to restore degraded habitats to functioning ecosystems is becoming more urgent. As many plant species used to restore grassland sites have low rates of germination and establishment, it is important for us to understand how this can be improved. The microorganisms within seed (seed endophytes) likely function as the primary inoculum of the plant microbiome. Seed endophytes isolated from crop species have been found to increase germination and plant establishment and there is potential for this advantage to be utilised in restoration.
We combined culturing and high-through-put-sequencing to characterise the taxonomic and functional diversity of both the bacterial and fungal seed microbiomes of two native Australian grass species commonly used in restoration. The seed were collected across multiple natural and restored sites and obtained from commercial seed production areas. We identified that microbial diversity is likely diminished and altered through seed processing and storage, with commercially produced seed having lower diversity, containing different abundant taxa relative to field collected seed. Using phenotyping assays of strains isolated from the field collected seed, we demonstrated the potential of several strains to improve plant growth. We performed mesocosm experiments with commercial seed inoculated with candidate strains, and assessed whether an increase in the number of positive traits was correlated with an increase in plant host fitness as measured through germination and other early seedling growth measurements. We present novel insights on the diversity and future applications of seed endophytes within restoration and seed preservation for conservation within Australia.