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

Abstract

inhibitors (BNIs). The chemical structure was analyzed which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH 4 + in the root environment and the stimulatory effect of NH 4 + 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 (ED 50 0.2 μM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED 50 100 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.

Potential for biological nitrification inhibition to reduce nitrification and N2O emissions in pasture crop–livestock systems

“…By contrast, Panicum maximum, which is adapted to high-N availability environments, showed the least BNI capacity among tropical pasture grasses (Subbarao et al, 2007b). Among the cereal crops evaluated, only sorghum (Sorghum bicolor), which is adapted to low N-input conditions showed significant BNI capacity (Subbarao et al, 2007b and2013a). Other cereal crops including rice, maize, wheat and barley lacked detectable BNI capacity in their root systems during the initial screening studies (Subbarao et al, 2007b andZakir et al, 2008).…”

“…The hydrophobic BNIs may remain close to the root as they could be strongly sorbed on the soil particles, increasing their persistence; their movement in soil is likely to be via diffusion across the concentration gradient and is likely to be confined to the rhizosphere (Dayan et al, 2010;Subbarao et al, 2012). In contrast, the hydrophilic BNIs may move further from the point of release owing to their solubility in water, and this may improve their capacity to control nitrification beyond the rhizosphere 2013a). However, the distribution of hydrophobic and hydrophilic BNIs in the rhizosphere likely differs and may have complementary functional roles such as differential inhibitory effects on AOB v. AOA (Subbarao et al, 2013a).…”

“…In contrast, the hydrophilic BNIs may move further from the point of release owing to their solubility in water, and this may improve their capacity to control nitrification beyond the rhizosphere 2013a). However, the distribution of hydrophobic and hydrophilic BNIs in the rhizosphere likely differs and may have complementary functional roles such as differential inhibitory effects on AOB v. AOA (Subbarao et al, 2013a). In sorghum, the production Figure 3 Schematic representation of the biological nitrification inhibition (BNI) interfaces in the N cycle.…”

“…In systems with little or no BNI, such as modern agricultural systems, nitrification occurs at a rapid rate, converting NH 4 1 to NO 3 2 , which is highly susceptible to loss from the system by denitrification and or leaching (adapted from Subbarao et al, 2012). and release of hydrophilic and hydrophobic BNIs appear to be of similar magnitude during crop development (Subbarao et al, 2013a). On the basis of the BNI activity release observed from a number of studies, we estimated that the amounts of BNIs (hydrophilic plus hydrophobic) released from sorghum during a 130-day growing period (i.e.…”

“…On the basis of the BNI activity release observed from a number of studies, we estimated that the amounts of BNIs (hydrophilic plus hydrophobic) released from sorghum during a 130-day growing period (i.e. nearly up to physiological maturity) can reduce nitrification in about 500 g soil per plant (Subbarao et al, 2013a).…”