Journal Article

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

Yoshida, M., Sahrawat, K. L., Zhu, Yiyong, Deshpande, S. P., Ono, H., Nakahara, K., Ishikawa, T., Yoshihashi, T., Hash, C. T., Zakir, H. A. K. M., Subbarao, G. V.

2013

Overview

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 includes inhibitor production, their chemical identity, functionality and factors regulating their release. Methods Sorghum was grown in solution culture and root exudate was collected using aerated NH4Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided chromatographic 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 ATU g−1 root dwt. d−1. Addition of hydrophilic BNIs (10 ATU g−1 soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated are: 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.

• Publisher: Springer Netherlands,Springer,Springer Nature B.V
• Subject: 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 / chemical structure / Ecology / Environmental aspects / Fractionation / Fundamental and applied biological sciences. Psychology / General agronomy. Plant production / Life Sciences / Mass spectrometry / Nitrification / nitrification inhibitors / Nitrogen content / Nitrosomonas / Nitrosomonas europaea / nuclear magnetic resonance spectroscopy / nutrient use efficiency / Plant biology / Plant Physiology / Plant roots / Plant Sciences / Plant-soil relationships / Plants / production technology / propionates / Regular Article / Rhizosphere / Root exudates / Roots / soil / Soil chemistry / Soil microorganisms / Soil Science & Conservation / Soil sciences / Soil-plant relationships. Soil fertility / Soil-plant relationships. Soil fertility. Fertilization. Amendments / Soils / Sorghum