Variovorax paradoxus alleviates bicarbonate-induced Fe limitation in cotton by altering the root-associated microbiome
Year: 2026
Type: preprint
Abstract: Alkaline and calcareous soils can induce iron (Fe) limitation in plants, yet the responses of root-associated microbial communities to beneficial rhizobacteria under these conditions remain poorly understood in cotton. Here, we investigated the effects of Variovorax paradoxus on plant performance, Fe nutrition, and root-associated microbiome dynamics in cotton exposed to bicarbonate-induced Fe limitation. In this study, V. paradoxus inoculation under bicarbonate-induced Fe limitation significantly improved photosynthetic parameters, growth parameters, and tissue Fe status. V. paradoxus inoculation partially reduced Fe-deficiency-induced root ferric-chelate reductase activity without a significant increase in net rhizosphere CAS-reactive Fe-chelating activity. This response may reflect a reduced requirement for maximal Strategy I activation following improved plant Fe status. Despite improved plant health, V. paradoxus reduced root C levels, suggesting altered belowground carbon utilization associated with bacterial inoculation and stress conditions. Split-root experiments showed greater improvements in chlorophyll score and shoot growth following bilateral than unilateral inoculation, although the effects of increased inoculum dose and root exposure could not be distinguished. In autoclaved soil, V. paradoxus did not improve plant growth under Fe deficiency, suggesting a possible role for resident soil microorganisms. Although bacterial alpha diversity remained unchanged, V. paradoxus significantly altered bacterial community composition and enriched Cellvibrio together with the fungal taxa Funneliformis and Dominikia under Fe limitation. Exploratory network analysis identified Funneliformis and Serendipita as highly connected fungal taxa associated with V. paradoxus treatment under Fe limitation, while core microbiome and indicator species analyses identified additional candidate microbial partners, including Pseudomonas , Hydrogenophaga , Shinella , and Aquabispora . Spearman correlation analysis further associated Streptomyces with root Fe accumulation and biomass, while Epicoccum and Sordariales were positively associated with CAS-reactive Fe-chelating activity in cotton exposed to bicarbonate-induced Fe limitation and inoculated with V. paradoxus . These findings highlight the potential of V. paradoxus to improve cotton Fe nutrition under bicarbonate-induced Fe limitation and identify root-associated microbial taxa whose functional contributions require further validation.
Authors: Maruf Khan, Bishrant Pant, Ahmad H. Kabir
Institution: Lamar University
Language: English
Subfield: Plant Science
Domain: Life Sciences
SDGs: Zero hunger, Life on land
Open Access status: green
Funder: Lamar University
OpenAlex ID: W7203838003