Abstract
Soils and plant root rhizospheres have diverse microorganism profiles. Components of this naturally occurring microbiome, arbuscular mycorrhizal (AM) fungi and plant growth promoting rhizobacteria (PGPR), may be beneficial to plant growth. Supplementary application to host plants of AM fungi and PGPR either as single species or multiple species inoculants has the potential to enhance this symbiotic relationship further. Single species interactions have been described; the nature of multi-species tripartite relationships between AM fungi, PGPR and the host plant require further scrutiny. The impact of select Bacilli spp. rhizobacteria and the AM fungus Rhizophagus intraradices as both single and combined inoculations (PGPR[i] and AMF[i]) within field extracted arable soils of two tillage treatments, conventional soil inversion (CT) and zero tillage (ZT) at winter wheat growth stages GS30 and GS39 have been conducted. The naturally occurring soil borne species (PGPR[s] and AMF[s]) have been determined by qPCR analysis. Significant differences (p < 0.05) were evident between inocula treatments and the method of seedbed preparation. A positive impact on wheat plant growth was noted for B. amyloliquefaciens applied as both a single inoculant (PGPR[i]) and in combination with R. intraradices (PGPR[i] + AMF[i]); however, the two treatments did not differ significantly from each other. The findings are discussed in the context of the inocula applied and the naturally occurring soil borne PGPR[s] present in the field extracted soil under each method of tillage.
Highlights
Microbial associations between plant and soil are highly complex and provide a myriad of interactions with a wide range of plant and soil benefits including increased soil fertility and aggregation [1,2], improved plant immunity and defence [3], increased plant biomass and carbon sequestration [4]
A key question this study aims to address is, can the benefits of the Mycorrhizal helper bacteria (MHB) B. amyloliquefaciens be enhanced further in the presence of additional Arbuscular mycorrhizal (AM) fungi through co-inoculation? Further, is the benefit realised to a greater degree under different tillage regimes? The current study aims to investigate the nature of the tripartite relationship between selected Bacilli spp. rhizobacteria, AM fungi and winter wheat in the context of species applied as inoculants ([i]) and the naturally occurring soil borne species ([s]) under two tillage regimes, conventional soil inversion (CT) and zero tillage (ZT)
A multi-way ANOVA comparing inoculant and tillage treatment at the same sampling time indicated a significant difference between treatments for tiller number, a proxy indicator of plant growth, in winter wheat (p < 0.00001, df: 7, 71271, F value: 20.70)
Summary
Microbial associations between plant and soil are highly complex and provide a myriad of interactions with a wide range of plant and soil benefits including increased soil fertility and aggregation [1,2], improved plant immunity and defence [3], increased plant biomass and carbon sequestration [4]. This can be of commercial importance for the amplified nutrient availability produced from AM fungal acquired soil bound nutrients, such as phosphorus, improving crop health, biomass and yield [7]. AM fungi can provide benefits to the improvement of soil properties, such as carbon and aggregation [2,8]. In combination with Plant Growth Promoting Rhizobacteria (PGPR), soil fertility can be improved further [9]
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