The highly productive, modern horticulture is strongly dependent on the availability of fossil fuels and other external resources such as chemicals and fertilizers. On the other hand, there is a rising concern about the environmental sustainability of the production chain. These aspects are boosting the research aimed at analyzing the environmental performances of the horticultural products, mainly in terms of primary energy use (PEU) and CO2 emission (carbon footpr int ) . The general aim is to increase the use efficiency of external resources, without compromising the elevated production standard of modern orchards. This review discusses the biological CO2 fluxes naturally occurring in agroecosystems, depicts the main methodologies adopted for evaluating environmental impacts, and PEU and analyzes the available literature about C footprint and PEU of horticultural crops, with special reference to apple trees. The agro-ecosystems continuously exchange carbon with the atmosphere, absorbing CO2 through the photosynthesis and releasing part of it via respiratory processes. Studies in apple orchards have shown a positive net ecosystem carbon balance, indicating the ability of this agroecosystem to store carbon. Among the available methodologies to quantify the PEU and the carbon footprint, many authors have adopted the life cycle assessment (LCA), defined by ISO standard (ISO 14040:2006), which defines the environmental performance of goods and services in different impact categories. In highly productive apple orchards (yields > 60 t ha-1) the PEU ranges between 0.4 and 0.7 MJ kg-1, corresponding to carbon footprint of the apple from the “cradle to gate” of approx. 0.05 kg CO2eq kg-1 of apple. The main processes contributing to the total PEU or C footprint are often the use of fossil fuels and the fertilization practices. PEU and C footprint of fruits for the final consumers depend on the intensity of transformation, time of conservation and distance between the production and consumption area.
Keywords: Apple, carbon footprint, carbon cycle, greenhouse gases