Abstract/Summary

Climate change is altering global weather patterns, threatening food security for the growing global population. Terrestrial soils have the potential to store twice as much carbon (C) as the atmosphere. It is, therefore, essential to explore factors that affect terrestrial C sequestration. Perennial crops such as apple trees sequester C belowground in their roots and surrounding soil and could play an important role in mitigating rising CO2 levels and maintaining food production. However, factors influencing belowground C sequestration in apple trees are not fully understood. The overall aim of my thesis was to determine what attributes influence this process. This project explored several factors that may enhance or impede apple tree’s capacity to sequester C belowground throughout the orchard’s lifecycle. Five factors were identified: 1) rootstock variety, 2) scion variety, 3) increasing atmospheric temperature, 4) orchard age, 5) stored soil C post-grubbing, each with specific experimental aims. The results showed; 1) Rootstocks were not significantly different in amounts of soil C sequestered. Soil MBC showed significant declines across the three rootstocks between August and September’s destructive harvest (P = <0.0001). 2) There were some significant differences between scions in soil total % C, but not in other C fractions. Soil total C significantly increased under COP (P = 0.03) and Dabinett (P = 0.01) over eighteen months for pot grown trees. 3) An increase in UK temperature by 2oC was linked to increased belowground C sequestration across different apple cultivars. The 2oC above ambient tunnel was consistently higher in TC than the ambient tunnel (P between 0.01 and <0.0001), and the 4oC above ambient (P between <0.01 and <0.00001). 4) A decline in most soil C fractions as orchards aged was observed. Most significant declines occurred in orchards 6 years of age and under. 5) After grubbing, an initial significant loss of soil C occurred in the former tree stands during the two months following soil disturbance (Ruben P = 0.04 and Gala P =0.01), followed by potential recovery if grass re-colonises the former tree stands. In conclusion, increasing atmospheric temperature by 2oC had a significant positive effect, whereas age of orchards and grubbing had significant negative effect on soil C. Grafted scions could have an impact but require longer-term studies. Rootstocks showed no significant effects on C sequestration across the five months. This study suggested the potential of apple trees to sequester C belowground may not be what is expected, compared with other studies. All these factors must be considered for accurately assessing apple orchards’ belowground C sequestration potential, enabling growers to work towards C net zero.