Root-Zone Restriction Regulates Soil Factors and Bacterial Community Assembly of Grapevine

Abstract

Root-zone restriction induces physiological stress on roots, thus limiting the vegetative and enhancing reproductive development, which promotes fruit quality and growth. Numerous bacterial-related growth-promoting, stress-mitigating, and disease-prevention activities have been described, but none in root-restricted cultivation. The study aimed to understand the activities of grapevine bacterial communities and plant-bacterial relationships to improve fruit quality. We used High-throughput sequencing, edaphic soil factors, and network analysis to explore the impact of restricted cultivation on the diversity, composition and network structure of bacterial communities of rhizosphere soil, roots, leaves, flowers and berries. The bacterial richness, diversity, and networking were indeed regulated by root-zone restriction at all phenological stages, with a peak at the veraison stage, yielding superior fruit quality compared to control plants. Moreover, it also handled the nutrient availability in treated plants, such as available nitrogen (AN) was 3.5, 5.7 and 0.9 folds scarcer at full bloom, veraison and maturity stages, respectively, compared to control plants. Biochemical indicators of the berry have proved that high-quality berry is yielded in association with the bacteria. Cyanobacteria were most abundant in the phyllosphere, Proteobacteria in the rhizosphere, and Firmicutes and Bacteroidetes in the endosphere. These bacterial phyla were most correlated and influenced by different soil factors in control and treated plants. Our findings are a comprehensive approach to the implications of root-zone restriction on the bacterial microbiota, which will assist in directing a more focused procedure to uncover the precise mechanism, which is still undiscovered.

Keywords: bacterial community structuring; bacterial networking; grapevine; root-zone restriction; soil interactions; stress cultivation.

Figure 1

Relative abundance (%) of the significant bacterial phyla existing in rhizosphere soil (S), white roots (WR), leaves (L) and berries (B) at three phonological stages as full bloom (FB), veraison (V), and maturity (M). Root-zone-restricted plants are denoted as treatment (T) while control plants as (C).

Figure 2

Alpha diversity indices Chao1 and Shannon. (a) Rhizosphere soil, (b) white roots, (c) leaves and (d) berries at three growth stages with comparison to treatment and control.

Figure 3

Non-metric multidimensional scaling (NMDS) for evaluation of microbial communities in samples from treated and control plants at full bloom, veraison and maturity. (a) Rhizospheric soil, (b) white roots, (c) leaves, and (d) berries.

Figure 4

The sampling groups depicted in the colour dots, soil parameters with blue arrows and the most affected are mentioned in red colour. The smaller the p-value, the greater the significant impact of the overall influencing factors on the composition of the soil microbiota.

Figure 5

Pearson correlation between the edaphic soil factors and bacterial population in the soil. (a) Control plants, (b) treated plants.

Figure 6

Network analysis of grape rhizosphere and phyllosphere bacterial communities. ASVs with less than 10 total sequences and less than 5 samples were filtered out. Nodes denote different interacting phyla. The top 10 modules (phyla) with the most significant number of interacting nodes are shown with their respective colours. Node size is proportional to the abundance. Edges connect different nodes with red and green lines as positive and negative correlations, respectively. (a) Rhizosphere soil, (b) white roots, (c) leaves, (d) berry.