The effects of arbuscular mycorrhizal fungal colonisation on nutrient status, growth, productivity, and canker resistance of apple (Malus pumila)

We assess whether arbuscular mycorrhizal fungi (AMF) improve growth, nutritional status, phenology, flower and fruit production, and disease resistance in woody perennial crops using apple (Malus pumila) as a study system. In a fully factorial experiment, young trees were grown for 3 years with or without AMF (Funneliformis mosseae and Rhizophagus irregularis), and with industrial standard fertiliser applications or restricted fertiliser (10% of standard). We use two commercial scions (Dabinett and Michelin) and rootstocks (MM111 and MM106). Industrial standard fertiliser applications reduced AMF colonisation and root biomass, potentially increasing drought sensitivity. Mycorrhizal status was influenced by above ground genotypes (scion type) but not rootstocks, indicating strong interactions between above and below ground plant tissue. The AMF inoculation significantly increased resistance to Neonectria ditissima, a globally economically significant fungal pathogen of apple orchards, but did not consistently alter leaf nutrients, growth, phenology or fruit and flower production. This study significantly advances understanding of AMF benefits to woody perennial crops, especially increased disease resistance which we show is not due to improved tree nutrition or drought alleviation. Breeding programmes and standard management practises can limit the potential for these benefits

Evaluating the potential of arbuscular mycorrhizal fungi for improving apple (Malus pumila) orchard sustainability

Developing agricultural systems which are able to balance productivity and sustainability is critical for ensuring future food security. Arbuscular mycorrhizal fungi (AMF) are an important component of the soil microbial community and play a vital role in a range of essential ecosystem functions. Arbuscular mycorrhizal symbiosis is characterised by the exchange of carbon from host plants in return for nutrients captured in the soil by the fungi, however AMF may also provide important non-nutritional benefits such as improving host plant resistance to pathogens. AMF are known to form symbiosis with over 80% of land plants including many major crop plants and have therefore received recognition as a potential tool for improving sustainability of agro-ecosystems. Apple is the fourth most widely planted fruit crop globally and is known to form symbiosis with AMF. The potential for AMF to improve orchard sustainability has been recognised by the cider apple industry and led to the overarching aim of this thesis which is to evaluate the potential benefits of AMF for cider apple production and sustainable management. Using the combination of a semi-controlled growth experiment and a landscape scale sampling approach, this study has examined the benefit AMF can provide to growth, health and productivity of cider apple trees. Understanding impacts of orchard management upon AMF communities has been a key aim of this work due to the increasing body of research reporting reduced abundance and functioning of AMF within intensively managed agricultural environments. This study has characterised AMF communities naturally found within three major cider apple orchard management types and investigated how AMF communities are impacted by aspects of orchard management. Results from this thesis provide evidence that AMF are able to provide disease resistance benefits to apple and are therefore beneficial to apple production. Furthermore data from this thesis shows that irrespective of management, cider apple orchards are able to host naturally diverse AMF communities which show similarities to the AMF communities of woodland. Results from this thesis have significant implications for orchard management and have highlighted several areas for potential future research

Effect of earthworms on soil physico-hydraulic and chemical properties, herbage production, and wheat growth on arable land converted to ley

Effects of earthworms on soil physico-hydraulic properties, herbage production and wheat growth in long-term arable soils following conversion to ley were investigated. Seven intact soil monoliths were collected from each of four arable fields. One monolith per field served as a control. The other six were defaunated by deep-freezing; three were left defaunated (DeF) and three (DeF+E) were repopulated with earthworms to mimic pasture field density and diversity. The monoliths were planted with a grass-clover ley and inserted into pre-established ley strips in their original fields for 12 months. Hydraulic conductivity measurements at -0.5 cm tension (K0.5) were taken five times over the year. K0.5 significantly increased in summer 2017 and spring 2018 and decreased in winter 2017-18. K0.5 was significantly greater (47%) for DeF+E than DeF monoliths. By the end of the experiment, pores >1 mm diameter made a significantly greater contribution to water flow in DeF+E (98%) than DeF (95%) monoliths. After only a year of arable to ley conversion, soil bulk density significantly decreased (by 6%), and organic matter (OM) content increased (by 29%) in the DeF treatments relative to the arable soil. Earthworms improved soil quality further. Compared to DeF monoliths, DeF+E monoliths had significantly increased water-holding capacity (by 9%), plant-available water (by 21%), OM content (by 9%), grass-clover shoot dry biomass (by 58%), water-stable aggregates > 250 µm (by 15%) and total N (by 3.5%). In a wheat bioassay following the field experiment, significantly more biomass (20%) was produced on DeF+E than DeF monolith soil, likely due to the changed soil physico-hydraulic properties. Our results show that earthworms play a significant role in improvements to soil quality and functions brought about by arable to ley conversion, and that augmenting depleted earthworm populations can help the restoration of soil qualities adversely impacted by intensive agriculture