Nitrogen Deficiency Stimulates Sorgoleone Production in Sorghum Roots and lower Soil-nitrification and N2O Emissions
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Background and aims Plant-derived biological nitrification inhibitors (BNIs) offer an ecological strategy to suppress soil nitrification and improve nitrogen-use-efficiency (NUE) in agricultural systems. Sorghum ( Sorghum bicolor L.) roots release several BNIs, with sorgoleone identified as the primary hydrophobic-BNI compound. However, the influence of nitrogen (N) fertilization on root morphology and sorgoleone release remains insufficiently understood. Methods Two sorghum genetic-stocks differing in sorgoleone production capacity, high-sorgoleone (HS) and low-sorgoleone (LS) were evaluated using paper culture experiments under contrasting N-forms and levels, followed by two consecutive years of field validation. The inhibitory effects of sorgoleone on soil nitrification were further verified through exogenous applications in a soil microcosm study. Potential nitrification, abundances of ammonia-oxidizing archaea (AOA) and -bacteria (AOB), and N 2 O emissions were quantified. Results Nitrogen deficiency significantly enhanced sorgoleone production in both genetic-stocks regardless of N-form in both paper culture and field trials. This increase in sorgoleone release was strongly associated with greater root length and surface area. Exogenous application of sorgoleone markedly reduced soil nitrification, AOA and AOB populations, and N 2 O emissions in soil incubation experiments. In the field, HS consistently exhibited higher sorgoleone production, lower nitrification, reduced nitrifier abundance compared with LS, particularly under high-N conditions. Conclusions These findings demonstrate that N deficiency stimulates sorgoleone production through root morphological adaptation and that sorgoleone suppresses nitrification by inhibiting ammonia oxidizers. The study provides mechanistic and field-based evidence supporting the role of hydrophobic-BNI in regulating soil N transformations and mitigating N losses in agroecosystems.
