Microbial community shifts and nutrient alteration in rice rhizospheres induced by Fe functionalized magnetic...

Soil fertility degradation and low nutrient-use efficiency remain major constraints in sustainable rice cultivation, especially in acidic soils. Biochar-based nanocomposites have emerged as advanced tools to improve nutrient bioavailability and soil health. This study examines the influence of rice husk biochar (HB) and its Fe-functionalized nanoscale variant, magnetic nanocarbon husk biochar (MNHB), on soil physicochemical properties, early growth of Oryza sativa (rice), and rhizosphere microbial dynamics. MNHB exhibited a fixed carbon content of 49.6%, ash content of 17.4%, and strong thermal stability above 400 °C. Dynamic light scattering and zeta potential analyses confirmed nanoscale particle size (<100 nm) with a surface charge of -25 mV, indicating good colloidal stability. FE-SEM imaging verified nanoscale morphology (81.58 ± 17.22 nm). Application of MNHB (5%) significantly enhanced root length (15.7 ± 0.49 cm), shoot length (46.41 ± 1.89 cm), and biomass (48.9% above Control, 25.3% above HB; p < 0.05). Soil pH, electrical conductivity, organic carbon, and macronutrients (N, P, K) increased substantially, demonstrating improved nutrient cycling and bioavailability. Metagenomic sequencing revealed reduced microbial alpha diversity but a marked community shift favoring Pseudomonadota (∼20% increase) and enrichment of beneficial genera such as Streptomyces, Micromonospora, and Neurospora tetrasperma. This work lies in establishing that Fe-functionalization in biochar nanosystems not only enhances nutrient transformation and uptake efficiency but also selectively restructures the rhizosphere microbiome, thereby coupling nutrient enrichment with microbial modulation for sustainable soil fertility restoration and crop productivity improvement.