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Abstract
The goal of this thesis is to provide information that will help to restore sites degraded by human activities such as mining and poor agricultural practices. Agricultural production is the backbone of societal development, yet some practices employed by farmers can reduce the ability of the farms to produce the food and fibre society needs. Practices such as replacing perennial vegetation with ephemerals, over-fertilization, improper irrigation, and overgrazing are the major causes of agricultural land degradation. These practices severely alter the topsoil which contains beneficial microorganisms that promote plant establishment. However, restoration projects on degraded lands rarely consider microorganisms. Literature synthesis revealed that inoculating microorganisms to plants increases plant growth by 47%. Thus, the lack of microorganisms in land restoration may explain why efforts to recruit plants from seed during restoration projects have yielded mixed success.
The lack of consideration of microbes in restoration projects led me to develop the first microbial-inoculated soil seed moulds for restoration. The soil seed mould is a seed enhancement technique that embeds seeds in microbial-inoculated soils moulded in concave trays. The microbial-inoculated soil seed mould was tested on two native species: Triodia epactia and Acacia inaequilatera, in a mine-degraded field. Soil seed moulds inoculated with microorganisms increased seedling emergence but had no effect on seedling survival, and sometimes had a negative effect on plant growth. The microbial-inoculated soil seed mould also changed the microbial community composition in the soil without affecting microbial diversity. The results show that benefits obtained from microorganisms are only achieved at the early stages of plant establishment.
My study revealed that the effect of microorganisms on ecosystem services during dryland restoration can vary from limited positive effects on some specific ecosystem components to no effect (likely due to the high mortality of inoculated microorganisms), to detrimental effects on plant growth. These mixed microbial effects reflect the dynamic behaviour of microorganisms in soils, suggesting the need to build a stronger understanding of the mechanisms that influence microbial behaviour in soils. I hope that my thesis inspires microbial ecologists to develop more effective microbial strains that persist in soils and provide continuous benefits to the ecosystem.
