LAUSR

Abstract In this work, we investigated the relationship between root plasticity and root oxygen dynamics in the presence of plant growth-promoting rhizobacteria (PGPR). A gnotobiotic system was used to study how the root architecture, radial O2-loss patterns, and internal O2 transport of the eelgrass Vallisneria natans (Hydrocharitaceae) changed in response to inoculation with a common soil PGPR, Pseudomonas putida (KT2440). Our results showed no radial O2-loss barrier in the roots of V. natans, meaning that the entire root surface exhibited the same capacity for O2 release. However, this morphological trait stimulated external oxygen demand in KT2440, thus reducing internal root O2 transport. Moreover, the distribution of root hairs (RHs), which was modified by exposure to KT2440, also significantly impacted internal O2 transport. The altered RH distribution minimized oxygen loss on the upper half of the root, and dense adventitious roots with overlapping rhizospheres enabled a highly oxygenated zone around the root base. Thus, these changes protect roots against low oxygen conditions. Furthermore, the presence of many RHs on the roots’ lower halves can increase nutrient absorption from anoxic sediments. In conclusion, this study demonstrates a complex trade-off between root aeration and architecture in V. natans that may help this plant adapt to submerged conditions when KT2440 is present.