Background Each year, approximately 9.5 million metric tons of plastic waste enter the ocean with the potential to adversely impact all trophic levels. Until now, our understanding of the impact of plastic pollution on marine microorganisms has been largely restricted to the microbial assemblages that colonize plastic particles. However, plastic debris also leaches considerable amounts of chemical additives into the water, and this has the potential to impact key groups of planktonic marine microbes, not just those organisms attached to plastic surfaces. Results To investigate this, we explored the population and genetic level responses of a marine microbial community following exposure to leachate from a common plastic (polyvinyl chloride) or zinc, a specific plastic additive. Both the full mix of substances leached from polyvinyl chloride (PVC) and zinc alone had profound impacts on the taxonomic and functional diversity of our natural planktonic community. Microbial primary producers, both prokaryotic and eukaryotic, which comprise the base of the marine food web, were strongly impaired by exposure to plastic leachates, showing significant declines in photosynthetic efficiency, diversity, and abundance. Key heterotrophic taxa, such as SAR11, which are the most abundant planktonic organisms in the ocean, also exhibited significant declines in relative abundance when exposed to higher levels of PVC leachate. In contrast, many copiotrophic bacteria, including members of the Alteromonadales, dramatically increased in relative abundance under both exposure treatments. Moreover, functional gene and genome analyses, derived from metagenomes, revealed that PVC leachate exposure selects for fast-adapting, motile organisms, along with enrichment in genes usually associated with pathogenicity and an increased capacity to metabolize organic compounds leached from PVC. Conclusions This study shows that substances leached from plastics can restructure marine microbial communities with the potential for significant impacts on trophodynamics and biogeochemical cycling. These findings substantially expand our understanding of the ways by which plastic pollution impact life in our oceans, knowledge which is particularly important given that the burden of plastic pollution in the marine environment is predicted to continue to rise.

Worldwide, there is a strong need for new, innovative, large‐scale approaches to restoring diverse native vegetation. Seed‐based revegetation, while often employed, can suffer from low plant establishment. Various seed coating technologies have been widely employed for decades to promote efficient agricultural planting; however, a significant obstacle to the implementation of this technology for native species revegetation is the limited access to the expertise and techniques which are mostly confidential to and specialized for the agrochemical industry. Here we investigated whether the seeds of Australian native species may benefit from extruded pelleting, measuring both seedling emergence and early growth, and testing the pellets with and without the addition of a commercial plant probiotic. A manipulative glasshouse experiment was carried out with three treatments (bare seeded; standard pellets; pellets amended with a probiotic) for four native plant species. Incorporation of seeds within standard pellets was shown to maintain high percentages of emergence and improve growth of three of the tested species (Daviesia ulicifolia, Hardenbergia violacea, and Indigofera australis) in the glasshouse setting, with increases in mean biomass of 83, 385, and 1,002%, respectively. However, emergence in the fourth species (Bursaria spinosa) was low in all seed treatments, perhaps due to excessive sowing depth (bare seeds), while combined with being encased inside a pellet. Relative to the standard pellets, probiotic amended pellets did not impart further detectable emergence or growth benefits. Ultimately, these results highlight exciting prospects for the application of extruded seed pellets in facilitating efficient use of seed in the revegetation of some native species.

Soil microbes play important roles in plant health and ecosystem functioning, however, they can often be disturbed or depleted in degraded lands. During seed-based revegetation of such sites there is often very low germination and seedling establishment success, with recruitment of beneficial microbes to the rhizosphere one potential contributor to this problem. Here we investigated whether Australian native plant species may benefit from planting seed encapsulated within extruded seed pellets amended with one of two microbe-rich products: a commercial vermicast extract biostimulant or a whole-soil inoculum from a healthy reference site of native vegetation. Two manipulative glasshouse trials assessing the performance of two Australian native plant species (Acacia parramattensis and Indigofera australis) were carried out in both unmodified field-collected soil (trial 1) and in the same soil reduced in nutrients and microbes (trial 2). Seedling emergence and growth were compared between pelleted and bare-seeded controls and analyzed alongside soil nutrient concentrations and culturable microbial community assessments. The addition of microbial amendments maintained, but did not improve upon, high levels of emergence in both plant species relative to unamended pellets. In trial 1, mean time to emergence of Acacia parramattensis seedlings was slightly shorter in both amended pellet types relative to the standard pellets, and in trial 2, whole-soil inoculum pellets showed significantly improved growth metrics. This work shows that there is potential for microbial amendments to positively affect native plant emergence and growth, however exact effects are dependent on the type of amendment, the plant species, and the characteristics of the planting site soil.