Shift of Nitrogen Resources by biotic interaction in grapevine

Abstract

Grape phylloxera (Daktulosphaira vitifoliae Fitch), a monophagous pest of the grapevine, induces nodosities on the roots through its sap-sucking activity. Nitrogen status is one of the most important components for plant performance and biological processes. Previous studies on phylloxera and sap-feeding have shown altered nutrient flow in the plant and enhanced accumulation in the nodosities. Additionally, the carbon and nitrogen uptakes are correlated with water availability.We studied the sink-source relationships between different plant organs under biotic (phylloxeration) and a short drought stress was studied in 72 Pinot noir/5BB plants under semi-controlled field conditions. Leaves, healthy root tips, nodosities and phylloxera aphids were sampled from each category before, during, and after the drought stress and analysed through mass spectrometry for their δ13C ratio, nitrogen and carbon concentration as percentage of their dry weight.

The phylloxeration, which was not a significant factor without the drought, significantly reduced the nitrogen content in the leaves during water stress. The healthy root tips were affected by drought only in phylloxerated plants: an exchange of behaviour between the belowground organs was observed. The well-watered individuals accumulated nitrogen in their healthy roots, but not in the nodosities. Reversely, the drought-stressed individuals decreased the nitrogen of their healthy root tips and accumulated it in the nodosities instead. The sink strength of the nodosities is enhanced under water stress. Additionally, the roots of non-phylloxerated plants showed a significantly better recovery potential in terms of nitrogen accumulation compared to phylloxerated plants. The abiotic stress appeared to be an enabling factor for phylloxeration and conversely. Generally, the non-phylloxerated plants developed more biomass than phylloxerated plants, specifically in the roots.