The impact of arbuscular mycorrhizal fungal inoculation on the growth and nutrition of agricultural plant species

Abstract

Arbuscular mycorrhizas (AM) can improve the nutrition of plants by increasing the uptake of nutrients, including phosphorus (P), zinc (Zn), and other micronutrients. It is for this reason that AM are often cited as having an important role to plant in enhancing the yield and mineral nutrition of food crops and helping to meet the demands of a growing world population, especially in changing climate. However, interactions between the arbuscular mycorrhizal fungi (AMF), plant, and environmental factors are complex and highly variable. Therefore, an understanding of the effect of forming AM on the growth, yield, and nutrition of agriculturally important crops is critical in order to design a sustainable farming system that can best harness the benefits of AM. In this thesis, I focused on exploring the impact of single AMF species Rhizophagus irregularis on the growth and nutrition of a range of important crop and pasture species, and different crop genotypes. Then, I further assessed the impact of AM on plant nutrition by studying the bioavailability of Zn and iron (Fe) in durum wheat grain for the purpose of human nutrition. In Chapter two, the results demonstrated that arbuscular mycorrhiza formation in diverse host plant species resulted in different responses in root colonisation, growth, and nutrition. Furthermore, plant species was a much stronger driver than colonisation by arbuscular mycorrhizal fungus, especially the plant ionome. However, the formation of AM improved uptake of mineral nutrients such as P, Zn, and Cu of most plant species included in the experiment. The results of Chapter three showed that AM increased the phytic acid (PA) concentration of durum wheat grain, which has important implications for estimating the bioavailability of Zn and Fe. In Chapter four, I reported on the effects of forming AM on a group of ten diverse durum wheat genotypes. In this experiment, plant genotype had an important role in controlling the responses of plants to AM in terms of yield and nutrition. Additionally, AM increased the bioavailability Zn and Fe in durum wheat grain of some genotypes, but not all. In addition to exploring impacts of plant identity on arbuscular mycorrhiza formation and functioning, the impact of soil P and Zn nutrient addition, on AM was also studied. Soil P addition had a strong impact on both plant growth and nutrition. It not only improved the plant yield and but also had less obvious effects on AM such as suppressing root colonisation, reducing the concentration of grain Zn and Fe, as well as increasing PA concentration. In contrast, while soil Zn addition was not found to have significant effects on the growth response of both Medicago truncatula and durum wheat to AM of my study, it enhanced the bioavailability of Zn in durum wheat grain. Furthermore, through employing high-throughput phenotyping technology, in Chapter five, I found that AM can still positively affect the growth of plants even in high soil P conditions; a response that was not evident in the final harvest. Furthermore, the effect of AM on the plants’ growth changed over the life of the plant. This work highlighted the value of phenotyping approaches to the study of impacts of forming AM over the life of a plant as well as at a final harvest. In conclusion, the impact of AM on plant growth and nutrition is highly variable and context-dependent; there are many factors including plant species and genotypes, soil P and Zn availability and also temporal effects to consider. Therefore, it is important to discover the particular conditions where AM can benefit plants in practical agricultural systems, in both growth and nutrition of specific plants species/genotypes. The effect of AM on PA on the cereals grain is another important factor to consider in the context of human nutritional quality in cereal crops.