Analysis and modelling of tree shading impacts on apple fruit quality: case study with an agrivoltaic system

In a context of climate change, apple growers must protect their orchards from extreme climatic events and radiation, especially in Mediterranean climates. Shading orchards with dynamic agrivoltaic systems is an innovative protection solution to climate change. However, no study has focused on the impact of a severe and fluctuating shade caused by dynamic agrivoltaic systems on 'Golden Delicious' apple fruit quality. Fruit firmness, skin colour, dry matter content, soluble sugars, malic acid, and starch were assessed in a three-year study (2019- 2021) to highlight the effect of shading on 'Golden Delicious' apple fruit with an agrivoltaic system. The shading strategy used was a solar tracking to maximise shading from the solar panels (mean shading rate of 50-55%). Fluctuating shading did not impact fruit maturity (assessed through firmness and starch decline) and therefore harvest date was not altered in comparison with trees grown in open-field conditions (control). Fruits grown under the agrivoltaic system had the standards of marketable quality for the fresh market. However, shaded fruits were greener and with lower fruit dry matter content than control fruits. Shading also decreased the sugar/acid ratio and decreased starch concentration. Besides field observations, a modelling approach was also used to disentangle the effects of shading on carbon import to the fruit and on its metabolism. A fruit model of starch, soluble sugars, and other fruit compounds concentrations (organic acids, proteins, cell wall) over time was parameterized using 2019 and 2020 experimental data and validated with the 2021 results. This model takes as inputs the air temperature, fruit dry and fresh mass over time. Using a single set of parameters common to shaded and control fruits, soluble sugar and starch dynamics were well simulated for shaded and control fruits over time, highlighting that the differences in sugar concentrations under shading were mostly due to a change in water and carbon fluxes entering the fruit rather than a change in the internal metabolism of the fruit. This was useful to have a better understanding of the effect of shading on fruit quality.