Unlocking the potential of Rhodopseudomonas palustris as a biofertilizer: Soil factors and microbial partnerships governing enhanced free-living nitrogen fixation

Hanxiao Bian; Haifeng Lu; Pengyu Chen; Chaoyuan Wang; Guangming Zhang

doi:10.1016/j.envres.2026.124086

Unlocking the potential of Rhodopseudomonas palustris as a biofertilizer: Soil factors and microbial partnerships governing enhanced free-living nitrogen fixation

Environ Res. 2026 Feb 25:297:124086. doi: 10.1016/j.envres.2026.124086. Online ahead of print.

Authors

Hanxiao Bian¹, Haifeng Lu², Pengyu Chen¹, Chaoyuan Wang¹, Guangming Zhang³

Affiliations

¹ College of Water Resource and Civil Engineering, China Agriculture University, Beijing, 100083, China; Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, Beijing, 100083, China.
² College of Water Resource and Civil Engineering, China Agriculture University, Beijing, 100083, China; Key Laboratory of Agricultural Engineering in Structure and Environment, Ministry of Agriculture, Beijing, 100083, China; Sanya Institute, China Agricultural University, Sanya, 572025, China. Electronic address: haifenglu@cau.edu.cn.
³ School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin, 300401, China.

PMID: 41759879
DOI: 10.1016/j.envres.2026.124086

Abstract

Overreliance on synthetic nitrogen fertilizers poses environmental risks and undermines agricultural sustainability. Free-living nitrogen fixation (FNF) by diazotrophs is a promising alternative. Rhodopseudomonas palustris (R. palustris), a metabolically versatile phototrophic diazotroph, shows strong potential for nonsymbiotic nitrogen fixation; however, its contribution to soil nitrogen input and ecological mechanisms remains unclear. This study evaluates the FNF performance of R. palustris in nutrient-poor, acidic lateritic soil and fertile, near-neutral phaeozem using ¹⁵N₂ isotope tracing, microbial community profiling, and network analysis. In sterilized soils, R. palustris accounts for >99.8% of nifH transcripts, resulting in net nitrogen fixation increases of 7.31-mg N·kg^-1 in lateritic soil and 23.87-mg N·kg^-1 in phaeozem. Inoculation markedly enhances FNF in native soils, with low-dose inoculation in phaeozem reaching a peak net increase of 147.01-mg N·kg^-1, an 11.96-fold increase over the control. This enhancement results from cooperative networks of diazotrophic Cyanobacteria and heterotrophs, which account for 94.1% of the variation in FNF. In lateritic soil, high-dose inoculation yields 7.94-mg N·kg^-1, attributed to improved diazotroph survival and function under stress. Path analysis confirms that R. palustris exerts the strongest positive direct effect on FNF (β = 0.786, P < 0.001), primarily owing to its abundance and nifH transcript copy number. These findings reveal distinct soil-specific modes of regulation: under strong edaphic constraints (low pH, low nutrients, limited C supply), FNF enhancement depends mainly on establishing an active diazotrophic population, whereas in fertile soil, low-dose inoculation can promote cooperative microbial processes that increase net nitrogen input. These findings provide a mechanistic baseline for designing subsequent field evaluations under fertilization or reduced-fertilization regimes.

Keywords: (15)N(2) isotope tracing; Biofertilizer; Inoculation strategy optimization; Lateritic soil; Phaeozem; Purple nonsulfur bacteria.