Spatial distribution of coarse root biomass and carbon in a high-density olive orchard: effects of mechanical harvesting methods

The in situ 3D root architecture of Olea europea was described by a semi-automatic 3D digitizing approach, which permitted the estimation of the biomass and carbon content of coarse roots in the soil environment. Coarse roots, the skeleton of the root system, are of primary importance for soil exploration and plant anchorage and only recently have been recognized as playing a major role in long-term carbon sequestration. Despite this role, the 3D architecture of coarse roots represents a gap in knowledge on the biomass and carbon allocation within the root system and, consequently, below-ground carbon sequestration capacity. Using a semi-automatic 3D digitizing approach (3 Space Fastrak plus Long Ranger), the 3D distribution in the soil environment of coarse root biomass and C content and how these parameters were affected by manual and mechanical (trunk shaker) harvesting methods were quantified in a high-density olive orchard. The below-ground C content at stand level was estimated to be 11.93 Mg C ha(-1) and distributed at deeper soil layers (45-60 cm) in the form of first- and second-order branching roots. The present study also revealed that the mechanical harvesting method significantly increased both the angle of growth (0A degrees = vertically downwards) of first-order lateral roots and the stump biomass, but neither the biomass allocation nor the C content was increased within the first three branching orders.