Soil and rhizosphere bacteriobiome of wheat under combined humate and fly ash application

Abstract

The aim of the study was to exmine the effct of low rate of potassium humate application with and without fly ash (FA) on wheat roots rhizosphere bacteriobiome.

Location and time of the study. The microplot field experiment was conducted in three replicates in randomized design in 2022 in Novosibirsk (Russia).

Methods. Soil physical and chemical properties were determined by commonly used methods. Bacteriobiome structure and diversity were estimated by 16S rRNA genes (V3-V4 region) by metabarcoding.

Results. The study revealed large bacteriobiome diversity: on average 2472 and 2330 operational taxonomic units (OTU) in bulk and rhizosphere soil< respectively. Overall 9120 OTE were found, belonging to 929 genera, 438 families, 416 orders, 104 classes and 37 phyla. A quarter of the total OTUs number belonged to the Proteobacteria phylum; Actinobacteria phylum ranked second in OTUs number (10%), whereas Firmicutes, Bacteroidetes and Acidobacteria each accounted for 8% of the total OTUs number. The Actinobacteria dominated in the relative abundance of the total number of sequence reads (38-41%), with Proteobacteria (25-28%) and Acidobacteria (10-13%) following. The treatment with potassium humate without fly ash did not influence the relative abundance of genera in the bulk soil, but increased twofold the relative abundance of the genus when combined with FA. In the rhizosphere soil bacteriobiome potassium humate without FA increased the Nocardioides relative abundance 1.8 times, whereas in combination with FA increased Sphingomonas and decreased Spartobacteria_gis relative abundance.

Conclusions. Potassium humate treatment at a low rate resulted in small, but positive changes in soil and rhizosphere bacteriobiome despite the huge bacterial diversity, inherent for practically any soil, including the one used in this study. The effect of exogenic humate treatment involves a complex of various mechanisms, and detailed physiological and biochemical studies and meta-analysis of the published data are needed to understand the effect of low rate humate application on soil, plans and microorganisms.