Rhizosphere Legacy: Plant Root Interactions with the Soil and Its Biome

Existing rhizosphere literature is united in the shared concept that the rhizosphere represents a dynamic system, which is strongly influenced by the passage of time. This concept gives rise to the idea of “legacy”, in that the rhizosphere of one plant generation leaves a footprint in the soil system, which affects the generations that follow. However, the literature definitions of “legacy” presented to date focus only on alterations in the soil microbiome and the resultant effects of these changes on following generations of plants.
We have reviewed existing concepts around the rhizosphere and its legacy and proposed a broader consideration of the rhizosphere legacy, which incorporates physical, chemical and biological changes that potentially endure beyond the root that created it.
Given the complexity of the rhizosphere and the interactions of legacy effects across the physical, chemical and biological characteristics of the soil, a range of techniques is needed to sample and analyse this environment. Techniques employed to date depend upon the area of research expertise being undertaken and predominantly rely on destructive methodologies. Recent advances in micro-X-ray computed tomography has alleviated the constraints of destructive sampling, but still requires complementation with other techniques to determine the extent of the rhizosphere legacy. Existing limitations in this complementarity remains a challenge to rhizosphere research. In order to advance our understanding of the rhizosphere and its legacy, there needs to be continued advancement in the methods we employ, which pay homage to the fact that the rhizosphere remains a fluid and ever-changing dynamic environment.