Figure 2.

Main flood effects on bulk soil and rhizosphere microorganisms. Low oxygen (O₂) conditions induced by flooding impact the rhizosphere and bulk soil microbial composition by producing a switch from aerobic to anaerobic microorganisms. The continuous flow of microbes from bulk soil to rhizosphere (indicated in the lower part of the diagram) can impact the taxonomic composition of the rhizosphere. One of the most important effects of soil microbiome alterations due to flooding is the variation in the nutritional status of the soil. Regarding nitrogen, the inhibition of nitrifying microorganisms and the consequent boost of denitrifiers induce the consumption of nitrate (NO₃ ⁻) and nitrite (NO₂ ⁻) to produce different gaseous nitrogen forms (NO, N₂O, and N₂). Nitrogen limitation may ultimately affect different aspects of plant growth. Hypoxic conditions on bulk soil also induce methanogenic processes due to the degradation of the soil organic matter by anaerobic methanogenic microbes. This process culminates with the production of methane (CH₄) and CO₂, which can be released to the atmosphere through soil or plant tissues. These changes on rhizosphere and soil microbes can be mitigated through specific plant adaptations favoring O₂ transport (e.g., aerenchyma). Plant stress can alter the composition of the root exudates and, therefore, produce a dysbiosis on the rhizosphere. Plant stress (and indirectly microbial stress) could be mitigated by the presence of specific groups of microbes, such as the plant growth promoting rhizobacteria (PGPR), which cleaves the ethylene precursor ACC (1‐aminocyclopropane‐1‐carboxylate) through the release of ACC‐deaminases. Created with BioRender.com [Color figure can be viewed at wileyonlinelibrary.com]