Quantification of aboveground and belowground biomass and associated organic carbon in two olive cultivars (Arbosana and Picual) grown at high density

Accurate quantification of biomass and carbon accumulation in olives is crucial for optimizing agronomic management and assessing their role to climate change mitigation. This study, developed destructive and non-destructive methodologies to quantify above- and belowground biomass and carbon content in 7.5-year-old trees of two common olive cultivars (Arbosana and Picual) under Mediterranean conditions. The approach included the removal of three whole-trees per cultivar and combined assessment of above- and belowground biomass, rarely available for olive trees. Picual tended to accumulate more biomass (36.5 kg tree−1, on average) than Arbosana (27.5 kg tree−1), due to a greater investment in trunk and non-primary branches, whereas Arbosana allocated more biomass to leaves. In both cultivars, around 60% of the root biomass was within the top 25 cm of soil, and over 55% was concentrated in the root ball. Weighted average carbon concentration was 47% in aboveground biomass and 42% in roots. At the orchard scale, soil was the main organic carbon pool, around 76 t C ha−1, compared to 13–16 t C ha−1 in the tree biomass. Annual carbon accumulation in olive biomass ranged from 1.68 t C ha−1 yr−1 (Arbosana) to 2.16 t C ha−1 yr−1 (Picual), within the range of C fixation rates in Mediterranean agroecosystems. Destructive sampling better captured cultivar differences in biomass allocation and carbon accumulation, while the non-destructive method proved suitable for large-scale use. These results support integrating biomass allocation and carbon permanence into cultivar selection and management to enhance carbon sequestration and sustainability of olive grove systems. Picual cultivar showed a total biomass 33% higher than Arbosana cultivar. 60% of root biomass was found in the top 25 cm of soil in both cultivars. Organic carbon concentration averaged 47% in shoots and 42% in root biomass. Destructive method detected cultivar differences in biomass with greater precision. Mean C sequestration rates by olive trees were 1.68 (Arbosana) and 2.16 (Picual) t C ha−1 yr−1.