Enhancing Iron Nutrition in Citrus: Synergistic Roles of Proline-2′-deoxymugineic Acid in Root Physiology and Microbiome

Iron (Fe) deficiency severely impairs plant growth and
development
in calcareous soils. Proline-2′-deoxymugineic acid (PDMA),
a phytosiderophore analog that enhances Fe availability, alleviates
Fe deficiency in field and vegetable crops but remains untested in
perennial woody crops. Herein, we conducted pot and field trials on
citrus, integrating physiological assays, RNA sequencing, 16S rRNA
profiling, and metagenomics to evaluate PDMA/PDMA–Fe(III) effects
on Fe nutrition, yield, root gene expression, and rhizosphere microbial
dynamics. Results showed that PDMA/PDMA–Fe(III) significantly
improved citrus Fe nutrition-outperforming traditional EDTA–Fe(III)–
by increasing rhizosphere Fe availability, thereby increasing yield
and downregulating Fe uptake- and stress response-related genes,with
PDMA–Fe(III) had stronger suppression. PDMA–Fe(III)
minimally disrupted the rhizosphere microbiome, while PDMA recruited
plant growth-promoting rhizobacteria (e.g., Pseudomonas, Nitrospira); both treatments enriched
microbial carbon fixation pathways. Collectively, PDMA/PDMA–Fe(III)
represent eco-efficient Fe fertilizers for citrus orchards, providing
sustainable remediation of Fe deficiency in calcareous soils.