The Interaction between Plants and Rhizosphere Microbes

Abstract

Specific crops, such as wheat, maize and rice are among the most important crops globally. There are numerous varieties, for example Triticum aestivum, is the common wheat that is widely cultivated globally and has more than 20,000 known varieties. Phosphorus and nitrogen fertilis-ers are commonly used to improve crop yield; however, it is costly and inefficient and can dam-age the environment. In this circumstance, bio-fertilisers shadow a new future direction for us, which utilise the beneficial relationship between the plants and the microorganisms in the soil. A better understanding of their interaction would give the foundation of sustainable agriculture in the future.
This work investigates the growth and activity of rhizosphere microorganisms. The first re-sults chapter examined the effects of the arbuscular mycorrhizal (AM) fungus Rhizophagus irreg-ularis on the hyphosphere microbial community. The relative abundance of fungi (Ascomycota, Basidiomycota, Mucoromycota) was lower in inoculated samples compared to uninoculated controls, suggesting potential competition or inhibition by the AM fungus. The supplementation with nutrients increased hyphae numbers overall, but samples inoculated with R. irregularis still had lower hyphae numbers compared to uninoculated controls. Bacterial communities also showed selective enrichment of certain taxa like Alphaproteobacteria and Gammaproteobacte-ria. Overall, the study highlighted the complex interactions between AM fungi, bacteria, and fungi in the hyphosphere.
The second chapter explored the effects of natural and artificial root exudates on soil bacte-rial communities. Natural exudates from wheat, sorghum, and chicory shaped distinct microbial profiles compared to artificial exudates. Artificial exudates had dose-dependent impacts, partic-ularly enriching taxa from the phyla Actinobacteria, Firmicutes, and Proteobacteria, with Actino-bacteria being most consistently responsive. Enrichment patterns were often treatment-specific across different artificial exudate formulations. The study also revealed that volatile organic compounds (VOCs) produced by soils treated with artificial exudates influenced recipient soil communities. While patterns were less structured, volatiles from lower exudate concentrations produced more consistent changes in ASV abundance.
Work presented in the final chapter isolated and characterised bacteria from different soils and media, assessing their plant growth-promoting traits like phosphate solubilisation and in-dole-3-acetic acid production. Bacteria from minimal media exhibited greater plant growth pro-motion abilities compared to those from nutrient-rich media when tested on Arabidopsis. Whole genome sequencing revealed the phylogenetic diversity of the isolates, with certain clades like Streptomyces and Mesorhizobium showing consistent plant growth-promoting effects.
Overall, this research provides insights into the complex interactions between plants, fungi, and bacteria in soil, highlighting the potential of harnessing these relationships to improve plant growth and soil health for sustainable agriculture.

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Identifiers

ORCID for Marc Dumont: orcid.org/0000-0002-7347-8668

ORCID for Tiina Roose: orcid.org/0000-0001-8710-1063

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