Abstract
Arbuscular mycorrhizal (AM) fungi establish close interactions with host plants, an estimated 80% of vascular plant species. The host plant receives additional soil bound nutrients that would otherwise not be available. Other components of the microbiome, such as rhizobacteria, may influence interactions between AM fungi and the host plant. Within a commercial arable crop selected rhizobacteria in combination with AM fungi may benefit crop yields. The precise nature of interactions between rhizobacteria and AM fungi in a symbiotic relationship overall requires greater understanding. The present study aims to assess this relationship by quantifying: (1) AM fungal intracellular root structures (arbuscules) and soil glomalin as an indicator of AM fungal growth; and (2) root length and tiller number as a measure of crop growth, in response to inoculation with one of three species of Bacillus: B. amyloliquefaciences, B. pumilis, or B. subtilis. The influence of soil management, conventional (CT) or zero tillage (ZT) was a further variable evaluated. A significant (p < 0.0001) species-specific impact on the number of quantifiable AM fungal arbuscules was observed. The inoculation of winter wheat (Triticum aestivum) with B. amyloliquefaciences had a positive impact on AM fungal symbiosis, as indicated by an average of 3226 arbuscules per centimetre of root tissue. Bacillus subtilis increased root length significantly (p < 0.01) but decreased fungal symbiosis (p < 0.01). The inoculation of field soils altered the concentration of glomalin, an indicator of AM fungal growth, significantly (p < 0.00001) for each tillage treatment. The greatest increase was associated with B. amyloliquefaciences for both CT (p < 0.0001) and ZT (p < 0.00001). Bacillus subtilis reduced measured glomalin significantly in both tillage treatments (p < 0.0001 and p < 0.00001 for CT and ZT respectively). The interaction between rhizobacteria and AM fungi is variable, being beneficial or detrimental depending on species. This relationship was evident in both tillage treatments and has important implications for maximizing symbiosis in the crop plant-microbiome present in agricultural systems.
Highlights
Arable farming relies on supplementary nutrient application to improve and maintain crop development [1]
The current study investigates the impact of selected rhizobacteria species on Arbuscular mycorrhizal (AM) fungal abundance and host plant development in the presence and absence of tillage by soil inversion
Selected rhizobacteria are a valuable component of the rhizosphere it is important that they are not considered in isolation from other beneficial microorganisms, AM fungi especially
Summary
Arable farming relies on supplementary nutrient application to improve and maintain crop development [1]. Arbuscular mycorrhizal (AM) fungi may improve the efficiency of soil nutrient exchange via close symbiotic relationships formed with the host plant. Intracellular root cortical fungal arbuscules allow enhanced assimilation of the soil nutrients obtained by fungal mycelia radiating away from the plant rhizosphere, in exchange for plant derived photosynthetic carbohydrates [2]. The abundance of AM fungi may be enhanced by less invasive land management practices such as zero tillage (ZT) [2]. Other components of the soil microbiome, bacteria, have the potential to influence crop growth and AM fungi and crop symbiosis. The nature of this relationship and the impact of crop management variables such as tillage regime, is less well established
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