Soil Microbial Communities Altered by Titanium Ions in Different Agroecosystems of Pitaya and Grape

Abstract

Titanium (Ti) is an element beneficial to plant growth. Application of titanium to roots or leaves at low concentrations can improve crop yield and performance. However, the effect of titanium ions on the bulk soil microbial community of planted crops remains unclear. This study aimed to explore the effects of titanium on soil bacterial and fungal communities. Field surveys were conducted to determine the effect of titanium ions on bulk soil microbial communities in pitaya and grape plantations of Panzhihua and Xichang areas, respectively. Full-length 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing were performed using PacBio Sequel to further explore the composition and structure of soil microbiota. The application of titanium ions significantly altered the composition and structure of soil microbiota. Root irrigation with titanium ions in pitaya gardens reduced the diversity of soil fungi and bacteria. However, the decline in bacterial diversity was not statistically significant. Meanwhile, foliar spray of titanium ions on grapes greatly reduced the soil microbial diversity. The bulk soil microbiota had a core of conserved taxa, and titanium ions significantly altered their relative abundances. Furthermore, the application of titanium increased the interaction network of soil fungi and bacteria compared with the control group. Thus, titanium ions potentially improve the stability of the soil microbial community. IMPORTANCE Pitaya and grape are important cash crops in the Panzhihua and Xichang areas, respectively, where they are well adapted. Titanium is a plant growth-promoting element, but the interaction between titanium and soil microorganisms is poorly understood. Titanium ions are still not widely used for growing pitaya and grape in the two regions. Thus, we investigated the effects of titanium ions on soil microbial communities of the two fruit crops in these two regions. Microbial diversity decreased, and the community structure changed; however, the addition of titanium ions enhanced cooccurrence relationships and improved the stability of the community. This study provides a basis for the importance of titanium ion application in crop cultivation.

Keywords: Panxi areas; Panzhihua and Xichang areas; grape; pitaya; soil microbial communities; titanium ions.

FIG 1

(a, b) Upset and Venn plots of bacterial (a) and fungal (b) communities of the four soil samples. The Upset plot is composed of three parts: the horizontal bars on the left-hand side show the number of OTUs, the exclusive intersections are set (vertically connected filled dark circles) in the center of the plot, and the top vertical bar chart shows the intersection numbers. The different bar colors correspond to the four different groups of soil samples. The specific intersection data are marked in red, while the other intersection data without statistical significance are in black.

FIG 2

(a, b) Alpha diversity of microbial communities in the soil samples. Chao1 and Shannon indexes of bacteria (a) and fungi (b) are presented. Group differences were determined by Wilcoxon rank sum test (P < 0.05); *, 0.01 ≤ P ≤ 0.05; **, 0.001 ≤ P ≤ 0.01; ***, P ≤ 0.001.

FIG 3

(a, b) Principal coordinate analysis of bacterial (a) and fungal (b) community structures based on Bray-Curtis distance; pco, principal coordinate.

FIG 4

(a, b) Abundance of bacterial (a) and fungal (b) communities in soils planted with pitaya and grape.

FIG 5

(a to d) Effect of titanium on the relative abundance of bacterial and fungal communities in the soil. The families for Hp (a) and Vv (b) and genera for Hp (c) and Vv (d) are depicted. The number of asterisks indicates significant differences between treatments according to a one-way ANOVA and FDR adjustment (P < 0.05); *, 0.01 ≤ P ≤ 0.05; **, 0.001 ≤ P ≤ 0.01; ***, P ≤ 0.001.

FIG 6

(a, b) Effect of titanium treatment on the bacterial and fungal cooccurrence and coexclusion networks in pitaya and grape agroecosystems. Nodes represent individual OTUs; edges represent significant positive (pink) and negative (green) Spearman correlations (ρ > 0.6, P < 0.001). Node size is positively correlated with degree (the number of edges attached to a node). Data for HpCon (left), HpTi (right) (a), VvCon (left), and VvTi (right) (b) are shown.

FIG 7

The presumed mechanism of action of titanium ions in improving crop performance. The focus of our research is highlighted in orange, and the arrows indicate the logic of causality.

FIG 8

Sampling schematic diagram. CK, control check.