Long-Term Rock Phosphate Fertilization Impacts the Microbial Communities of Maize Rhizosphere

Abstract

Phosphate fertilization is a common practice in agriculture worldwide, and several commercial products are widely used. Triple superphosphate (TSP) is an excellent soluble phosphorus (P) source. However, its high cost of production makes the long-term use of crude rock phosphate (RP) a more attractive alternative in developing countries, albeit its influence on plant-associated microbiota remains unclear. Here, we compared long-term effects of TSP and RP fertilization on the structure of maize rhizosphere microbial community using next generation sequencing. Proteobacteria were dominant in all conditions, whereas Oxalobacteraceae (mainly Massilia and Herbaspirillum) was enriched in the RP-amended soil. Klebsiella was the second most abundant taxon in the RP-treated soil. Burkholderia sp. and Bacillus sp. were enriched in the RP-amended soil when compared to the TSP-treated soil. Regarding fungi, Glomeromycota showed highest abundance in RP-amended soils, and the main genera were Scutellospora and Racocetra. These taxa are already described as important for P solubilization/acquisition in RP-fertilized soil. Maize grown on TSP and RP-treated soil presented similar productivity, and a positive correlation was detected for P content and the microbial community of the soils. The results suggest changes of the microbial community composition associated to the type of phosphate fertilization. Whilst it is not possible to establish causality relations, our data highlights a few candidate taxa that could be involved in RP solubilization and plant growth promotion. Moreover, this can represent a shorter path for further studies aiming the isolation and validation of the taxa described here concerning P release on the soil plant system and their use as bioinoculants.

Keywords: maize rhizosphere; microbial community; rock phosphate.

FIGURE 1

Principal coordinate analysis (PCoA) of the bacterial and fungal communities of the maize rhizosphere grown without added P (control), with rock phosphate (RP), and with triple superphosphate (TSP). Analysis of similarity (ANOSIM) was made between among the P treatments. (A) Clustering similarity of bacteria using weighted UniFrac and (B) using unweighted UniFrac. (C) Clustering similarity of the fungal community using the Bray–Curtis metric.

FIGURE 2

Relative abundance of (A) bacterial phyla, (B) families, and (C) genera. (D) Fungal phyla, (E) families, and (F) genera. Taxa occurring in at least one condition with an abundance greater than 3% were considered, and variance analysis was performed between P treatments, followed by Scott Knott test at 5%. For each taxon, means with the same letter are not significantly different. Control, treatment without added P; RP, treatment with rock phosphate; TSP, treatment with triple superphosphate; nd, identification was not possible at the family level.

FIGURE 3

Significance analysis of the relative abundance of the taxa until family level (threshold of 0.1%) for bacterial (A) and fungal (C) communities using the edgeR analysis. In the volcano plot (A and C), the taxa that differ between RP and TSP treatments are showed above dashed line of the y-axis, corresponding to 0.05 of p-value and x-axis represents the fold changes in relative abundance (log2) of the taxa between treatments. Relative abundance only of the significant taxa in the edgeR analysis (volcano plot) for bacteria community (B) and (D) fungi community of the RP compared to TSP.

FIGURE 4

Non-metric multidimensional scaling (NMDS) of the composition of the (A) bacterial community and (B) the fungal community using a Rho metric. The samples were plotted with fitted environmental variables (biomass of the plant, grain yield, and P in the soil at the end of the experiment). Arrows indicate the direction of the correlation with the microbial community. For community composition, an OTU richness and phyla abundance with more than 1% of relative abundance were used. Treatments: soil without added P (control), soil treated with rock phosphate (RP), and soil with added triple superphosphate (TSP).