Effect of chemical fertilizer application on selection of beneficial rhizobacteria in wheat

Rhizocompartments (rhizosphere and rhizoplane) hold distinctive and selective microbiomes when compared to bulk soil, however little is known about the effect chemical fertilizer has on the function of rhizobacterial communities. Here, we investigated how the addition of nitrogen-phosphorous-potassium (NPK) fertilizer affects bacterial community composition, diversity, and functionality within rhizocompartments of wheat, using both culture-independent and dependent methods. Triticum aestivum cv. Cadenza seeds were grown in nutrient-depleted agricultural soil in pots treated with and without fertilizer. As expected, fertilizer application reduced rhizobacterial diversity and richness and affected the structure and composition of wheat rhizobacterial communities. Rhizosphere- and rhizoplane-derived microbiota culture collections were established and tested for plant growth-promoting traits using functional bioassays. In general, fertilizer addition decreased the proportion of plant growth-promoting rhizobacteria isolated from rhizocompartments in wheat. Bacterial isolates capable of solubilizing organic nitrogen, phosphate and potassium were significantly reduced when inorganic fertilizer was applied. Furthermore, there was an increased selection of beneficial microbes in the rhizoplane when compared with the rhizosphere of wheat roots. Our study suggests that addition of fertilizer reduces the selection of beneficial rhizobacteria in wheat. This knowledge will benefit the development of agricultural practice strategies which are less dependent on interventions such as current agronomic fertilizer applications.