Biological nitrification inhibition (BNI) activity in sorghum and its characterization

Aims The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed 'biological nitrification inhibition' (BNI). Here, we aimed at the quantification and characterization of the BNI function in sorghum that included inhibitor productio...

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Published in:	Plant and soil Vol. 366; no. 1/2; pp. 243 - 259
Main Authors:	Subbarao, G. V., Nakahara, K., Ishikawa, T., Ono, H., Yoshida, M., Yoshihashi, T., Zhu, Yiyong, Zakir, H. A. K. M., Deshpande, S. P., Hash, C. T., Sahrawat, K. L.
Format:	Journal Article
Language:	English
Published:	Dordrecht Springer 01-05-2013 Springer Netherlands Springer Nature B.V
Subjects:	Agricultural research Agricultural soils Agrology Agronomy. Soil science and plant productions Animal, plant and microbial ecology Bioassays Biological and medical sciences Bioluminescence Biomedical and Life Sciences Cereals Ecology Environmental aspects Fractionation Fundamental and applied biological sciences. Psychology General agronomy. Plant production Life Sciences Mass spectrometry Nitrification Nitrogen content Nitrosomonas Nitrosomonas europaea Plant biology Plant Physiology Plant roots Plant Sciences Plant-soil relationships Plants Regular Article Rhizosphere Root exudates Roots Soil chemistry Soil microorganisms Soil Science & Conservation Soil sciences Soil-plant relationships. Soil fertility Soil-plant relationships. Soil fertility. Fertilization. Amendments Soils Sorghum Japan Activity-guided isolation Sorgoleone HAO (hydroxylamine oxidoreductase) Hydrophilic and hydrophobic nitrification inhibitors Ammonia monooxygenase (AMO) Biological nitrification inhibition (BNI) Sorghum BNI compounds Sakuranetin Monocotyledones Nitrogen compounds Activity Biology Hydrophobicity Inorganic element Characterization Gramineae Angiospermae Inhibition Macronutrient(mineral) Hydroxylamine Enzyme Life science Nitrification inhibitor Physical properties Hydrophily Ammonia Nitrogen cycle Inorganic nitrogen Nitrification Isolation Herbaceous plant Spermatophyta Oxidoreductases Soil plant relation
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Summary:	Aims The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed 'biological nitrification inhibition' (BNI). Here, we aimed at the quantification and characterization of the BNI function in sorghum that included inhibitor production, their chemical identity, functionality and factors regulating their release. Methods Sorghum was grown in solution culture and root exúdate was collected using aerated NH₄Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided Chromatographie fractionation was used to isolate biological nitrification inhibitors (BNIs). The chemical structure was analyzed using NMR and mass spectrometry; pH-stat systems were deployed to analyze the role of rhizosphere pH on BNIs release. Results Sorghum roots released two categories of BNIs: hydrophilic- and hydrophobic-BNIs. The release rates for hydrophilic- and hydrophobic- BNIs ranged from 10 to 25 ATUg⁻¹ root dwt. d⁻¹. Addition of hydrophilic BNIs (10 ATUg⁻¹ soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated were: sakuranetin (ED₈₀ 0.6 µM; isolated from hydrophilic-BNIs fraction) and sorgoleone (ED₈₀ 13.0 µM; isolated from hydrophobic-BNIs fraction), which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH₄⁺ in the root environment and the stimulatory effect of NH₄⁺ lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED₅₀ 0.2 µM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED₅₀ 100 µM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay. Conclusions There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0032-079X 1573-5036
DOI:	10.1007/s11104-012-1419-9