Abstract
The mass transfer from root to soil by means of rhizodeposition has been studied in grasses and forest trees, but its role in fruit trees is still unknown. In this study, N
fluxes from roots to soil were estimated by applying a 15N mass balance technique to the soil–tree system. Apple (Malus domestica) trees were pre-labelled with 15N and
then grown outdoors in 40 L pots for one vegetative season in (1) a coarse-textured, low organic matter soil, (2) a coarse-textured, high organic matter soil, and (3) a finetextured, high organic matter soil. At tree harvest the 15N abundance of the soils was higher than at transplanting, but the total amount of 15N present in the tree–soil system was similar at transplanting and tree harvest. The soils had a
strong effect on N fluxes from and to the soil. In the finetextured soil, 11% of the total plant-derived nitrogen was transferred to the soil, compared with 2–5% in the two
coarse-textured soils. Rhizodeposition was higher in the fine soil (18% of the primary production) than in the coarse-textured soils, whereas higher soil organic matter
depressed rhizodeposition. Nitrogen uptake was almost double in the coarse-textured, high organic matter soil versus the other soils. Our results indicate that belowground
primary productivity is significantly underestimated if based on root production data only. Rhizodeposition represents a major process, whose role should not be
underestimated in carbon and nitrogen cycles in orchard ecosystems.