Productivity in grain agricultural systems across Australia are constrained by dense clay subsoils. Past research has shown the addition of nutrient rich amendments directly to the subsoil has led to significant long-term improvements in soil quality and crop production. It is hypothesied that the microbial community response to amendment addition contributes to the amelioration effect. In this study, a planted column experiment was designed to discern the effect of different subsoil amendments on bacterial communities within a controlled environment. The bacterial response was examined through 16S rRNA next-generation sequencing and correlated with soil chemistry and structural measurements.
Differential abundance and beta-diversity analyses was utilised to unravel bacterial taxonomic response to amendment addition, while predictive function profiling via PICRUSt2 was utilised to provide insight into the potential functional response. When comparing treatments to their appropriate controls, the majority of the observed bacterial functional and taxonomic differences were driven by an synergistic effect between the amendment and the plant roots, rather than an effect of either the amendment or the plant in isolation. Interestingly, this synergistic effect between the amendment and the plant roots was shown to shift the bacterial community structure rather than simply enhancing it. Differential abundance analysis indicated minimal differences between amendment types, highlighting the observed bacterial response is the result of the amendments interaction with the plant rather than a direct effect on the bacterial composition.
Overall, results indicate bacterial community changes post-amendment addition are due to an indirect effect of subsoil amendments whereby the amendments stimulate the plant metabolism which drives a bacterial response possibly through changes occurring within the root network and surrounding soil.
Although this study occurred within a controlled environment, it highlights the necessity of actively growing plants to drive microbial changes which may assist in subsoil amelioration. Grain agricultural systems looking to potentially ameliorate problematic subsoils may need to consider actively growing crops all year round rather than the commonly practiced seasonal approach.