Effect of organic fertilization on carbon assimilation and partitioning in bearing nectarine trees

The aims of this study were to evaluate the effect of organic fertilization on carbon dioxide (CO2) fixation, carbon (C) partitioning and growth of potted nectarine trees (Prunus persica L. Batsch), cv. ‘Orion’, to verify the hypothesis that organic fertilizers may promote root growth to the detriment of canopy and fruit biomass. The following four treatments were compared as in a complete randomized block design: unamended control, cow manure at a rate of 20 g dry weight (DW) kg soil fresh weight (FW−1), compost (20 g DW kg soil FW−1) and compost (60 g DW kg soil FW−1). Trees were potted in 40 L-pots with a clay-loam Bathicalci Eutric Cambisols soil and sand at a rate of 3:1. Tree canopies were labeled with 99% 13C enriched CO2 and nineteen days after the pulse and at the end of the vegetative season, 3 trees per treatment were harvested and analyzed. The addition of compost at the highest rate was effective in increasing CO2 fixation, promoting root and shoot growth, with no effect on fruit biomass, compared to the unamended control. The higher CO2 fixation was the result of a larger tree growth rate and leaf area, rather than an increase in leaf photosynthetic efficiency. The involvement of nitrogen (N) uptake was not clear, since N leaf concentration was decreased by organic fertilizations.

► Soil application of compost at 60 g DW kg soil FW increased whole canopy nectarine tree CO2 fixation.
► Compost application also promoted root and shoot growth, with no change of root:shoot ratio.
► The higher CO2 fixation rate was the result of a larger tree growth rate and leaf area.
► The positive effect on tree growth was not supported by an increase in soil mineral N.
► Compost treated trees increased their efficiency of N remobilization and storage to the roots.