Effects of olive shoot residues on shoot and root growth of potted olive plantlets

• Application of olive shoot residues (OSR) close to the roots temporally inhibited root and shoot growth.
• OSR increased organic matter and nitrogen contents of the pot substrate.
• OSR increased proportionally polyphenol contents of the pot substrate.
• OSR incorporation altered fine root respiration and electrolyte leakage.
• 240 days after application, OSR positively affected fine root and shoot relative growth rate.

Decomposition of olive shoot residue (OSR) from leaf shedding and pruning may provide nutrient to olive orchards, although beyond a phytotoxic threshold it can also hamper plant growth. We studied OSR decomposition effects on plant growth, biomass partitioning and soil fertility. Four levels of OSR (0%, 3%, 10% and 30% [v/v]) were mixed into the substrate and placed close to the roots compared on two olive potted cultivars over 240 days using a destructive sampling approach. Organic matter, polyphenol and nitrogen contents in the substrate, fine root respiration and electrolyte leakage, leaf pigment content, chlorophyll a fluorescence, biomass partitioning, fine root nutritional status were determined. OSR increased the content of organic matter, polyphenols and nitrogen in the soil. In the first 150 days, OSR beyond 3% induced autotoxic effects, and altered fine root respiration, and electrolyte leakage and biomass allocation. After 240 days, OSR induced a stimulatory effect on fine roots and shoot growth and increased shoot and fine root nitrogen content. Application OSR did not significantly altered leaf pigment content and chlorophyll a fluorescence. As a conclusion, above the threshold of 3%, olive cannot prevent autotoxicity during the early decomposition of OSR, but later soil fertility and plant growth can be increased.