Biomass and carbon allocation in above and belowground parts of two olive cultivars at high-density

Accurate measurements of biomass production and carbon storage in olive groves are needed to improve crop management and evaluate their role in mitigating climate change impacts. Two approaches, destructive and non-destructive, were set up to estimate aboveground and belowground biomass, as well as carbon content, in a total of six 7.5-year-old trees of two olive cultivars, Arbosana and Picual, grown under Mediterranean field conditions. This was complemented by determining soil organic carbon storage at the root system depth (1.30 m). The findings indicated that Picual produced higher total biomass (36.5 kg tree^-1) compared to Arbosana (27.5 kg tree^-1), largely because Picual accumulated more biomass in structural elements, such as the trunk and secondary branches. In contrast, Arbosana allocated more biomass to the foliage. In both cultivars, roughly 60 % of root biomass was located within the first 25 cm of soil, and more than 55 % was concentrated in the root ball. In both cultivars, the average carbon concentration in biomass was 47 % in aboveground plant parts and 42 % in the root system. At the orchard level, the soil acted as the primary organic carbon reservoir, containing about 76 t C ha⁻¹, while the total tree biomass stored around 13-16 t C ha⁻¹, with 4.1-5 t C ha⁻¹ stored in the root biomass. The mean annual carbon accumulation in olive biomass ranged from 1.68 t C ha⁻¹ yr⁻¹ for Arbosana to 2.16 t C ha⁻¹ yr⁻¹ for Picual, values consistent with carbon sequestration rates reported for other Mediterranean agricultural systems. While the destructive methodology provided more accurate differentiation between cultivars in terms of biomass and carbon content, the non-destructive method proved more practical and suitable for larger-scale implementation, albeit with a moderate reduction in accuracy. Overall, these results support the integration of biomass and carbon data into olive cultivar selection and management practices, with the aim of enhancing carbon sequestration and promoting the long-term sustainability of olive production systems.

Acknowledgement: This work has been supported by the projects MARVIC “Monitoring, reporting and verification of soil carbon and greenhouse gases balance” (101112942), ECOMED "Improving soil cover assessment strategies in Mediterranean agricultural areas” (PR. AVA23.INV202301.035), Operational Group “Olive Carbon Balance” (OCB) from EIP-Agri (REGAGE23e00065250685), Qualifica Project QUAL21_023 IAS, PID2023-146177OB-C21 and PID2023-146177OB-C22 projects funded by MICIU/AEI /10.13039/501100011033 and FEDER, UE, and “ERDF A way of making Europe” by “ERDF/EU”