Strigolactone GR24 modulates citrus root architecture and rhizosphere microbiome under nitrogen and phosphorus deficiency

Nutrient deficiencies, especially nitrogen (N) and phosphorus (P) deficiencies, are among the most critical challenges for sustainable crop production. Excessive use of chemical fertilizers contributes to environmental degradation and climate change, highlighting the need for alternative strategies to improve nutrient uptake. Strigolactones (SLs), a class of plant hormones, have emerged as key regulators of root development and plant-microbe interactions under nutrient-limited conditions. In this study, we investigated the effects of the SL analog GR24 on citrus rootstock C-32 under full nutrition, nitrogen deficiency, and phosphorus deficiency conditions. Plants were treated with five GR24 concentrations (0, 1, 2.5, 5, and 10 µM) and evaluated for changes in root architecture, biomass, soil nutrient content, and rhizosphere microbiomes. The results showed that SL application had a concentration-dependent effect on root morphology. The 2.5 µM SL treatment enhanced fine root initiation, proliferation, and lateral branching under nutrient deficiency, whereas higher concentrations (5 and 10 µM) generally had inhibitory effects. Root surface area and volume were modulated differently across diameter classes, depending on nutrient status and SL dose. Soil nutrient analyses indicated minor alleviating effects of SL on N and P starvation; however, SL significantly affected Cu and Mn. Microbiome analysis revealed that SL reduced bacterial ASV richness but increased dispersion in community structure, particularly under N and P deficiency. Functional annotation indicated changes in denitrification and methanotrophy pathways. Overall, SLs modulated both the root architecture and rhizosphere microbiome composition of citrus plants under nutrient stress. These findings suggest a dual role for SLs in enhancing root plasticity and microbial recruitment, with potential applications in sustainable crop nutrition and soil health.