Global environmental changes and other anthropogenic impacts are rapidly transforming the structure and functioning of ecosystems worldwide. These changes are leading to depletion of native plant communities and soil degradation with an estimated 25% of the global land surface being affected. Developing cost-effective and large-scale solutions to restore disturbed landscapes is crucial to preserve biodiversity and achieve ecosystem functionality and sustainability. Indigenous soil bacteria, including cyanobacteria from soil biocrusts, have shown promise as bio-fertilizers as they may promote seedling growth of native plants in reconstructed soil profiles. However, the use of these bio-inoculants in restoration programs is challenging and new approaches for landscape-scale application need to be explored.
In this research we assessed the potential of bioinoculants composed of locally sourced soil bacteria from the rhizosphere and cyanobacteria from biocrusts, to (i) promote germination and growth of native plants used in mine site restoration in Australia’s arid north-west, and (ii) restore fertility of degraded soils and substrates. Individual cyanobacteria species (e.g. Leptolyngbya sp, Nostoc sp., Scytonema sp. and Microcoleus sp), mixes of these species, and enrichments of soil bacteria from the rhizosphere, were considered as inoculum. These inocula were applied as seed bio-primers or directly inoculated within extruded pellets of topsoil material.
Results/Conclusions
The effects of the cyanobacterial/bacterial inoculants were specific to each plant species. However, biopriming seeds with soil bacteria and the cyanobacteria mix resulted in three times larger seedling roots in hummock grasses (e.g. Triodia epactia) compared to the control treatment. The positive effects of the native soil bacteria and cyanobacteria inoculants on native plants can be related to their ability of promoting nutrient bioavailability, improving stress resistance, protection against other microbes, and production of substances that may act as hormones. Through GC/MS analyses we identified the bio-active components or metabolites produced by targeted cyanobacteria species which included substances chemically like plant hormones such as auxins, i.e. indole-3-acetic acid.
Our results also showed that cyanobacteria can be successfully incorporated into extruded soil pellets and redistributed via watering to modify properties of degraded soil substrates, by increasing soil carbon contents and microbial diversity. Overall, the findings of this research will allow selecting the most effective bio-active inoculants for application in seed-based land restoration programs.