Root-microbe Interactions in Response to Soil Conditions.

Many recent studies have confirmed that plant beneficial microbes can improve plant nutrition, plant growth and alter plant phenotype to improve fitness. However, plant beneficial microbes are not easy to outline, as their function and structure can vary due to many factors including soil conditions. Soil microbiome is in flux with soil conditions, as some soil conditions can be constraints for microbial growth and function like moisture stress (transient soil condition), acidity and alkalinity (inherent soil condition). For example, during drought plant microbiome is significantly altered in many crops, and plants may select for microbes to improve drought tolerance. Studies have shown that microbial phylogenetic and physiological adaptations in response to moisture stress are commonly observed. Similarly, soil microbiome can vary due to inherent soil constraints as well. Subsoil in most areas have some type of soil constraints including acidity, aluminum or salts toxicity, hypoxia and compactness. Plant-microbe interactions are critical to improve root fitness in subsoil. Some evidence exists on microbiome response to soil constraints, however not much is known regarding the relationships between root and microbiome phenotypes. It is still unclear whether roots recruit different microbes in response to subsurface soil conditions (constraints) compared to surface layer. Soil constraints can be detrimental to some plant beneficial microbes like mycorrhizae, which usually diminish with depth. Understanding root-microbe interactions can help develop root-microbiome phenotypes to efficiently explore subsurface soil layers for water and nutrients.