Phosphorus Deficiency Induced Silicon Mobilization in Grapevine Rhizosphere: A Field Study

Abstract

Silicon (Si) uptake by crops is well studied and Si transporters have been characterized in various crop species, including grapevine. However, information on the rhizosphere mobilization of Si is still lacking and virtually no information is available on grapevine. Our previous study showed that grapevine is a phosphorus (P)-efficient species with a high root capacity to mobilize P from the rhizosphere by the released of organic anions (mainly citrate). The field experiment was established in 12-y-old vineyard with the cultivar ‘Chardonnay’, grafted on 5BB rootstock under extremely low P conditions (Olsen P < 3 mg kg-1). Four own-designed rhizotrons (80 cm depth) were installed in a vineyard enabling easy access to the new intact roots. The following treatments were performed: –P/–Si, +P/–Si, –P/+Si (soil application) and –P/+Si (foliar application). The samples of rhizosphere and bulk soils, root exudates from intact root tips and vine tissues (root and leaves) were collected at different growth stages according to Eichhorn-Lorentz (E-L) system: flowering (E-L stage 23), berries pea-size (E-L stage 31), and veraison (E-L stage 35). In addition to Si and P concentrations in the tissues, the expressions of VvALMT, VvMATE (encoding efflux transporters for malate and citrate, respectively), and VvNIP2.1 (encoding Si influx transporter) were also determined. Phosphate fertilization decreased, while low soil P and Si fertilization increased Si availability in the rhizosphere. At the flowering stage, –P plants accumulated more Si than the P-fertilized ones and was comparable to the Si-fertilized plants. Foliar application of Si was less effective in comparison with soil application unless at the veraison stage. The leaf Si concentrations showed a clear seasonal pattern being the highest at the veraison stage. Exudation rate of citrate also showed a clear seasonal pattern and was significantly higher in the –P/–Si than in +P/–Si plants, which was followed by an increased Si availability in the vine rhizosphere. Overall, low P conditions induced Si accumulation in the leaves due to increased exudation of organic anions that can also mobilize Si in the rhizosphere, thereby increasing Si uptake by grapevine.