Biological nitrification inhibition byBrachiaria humidicolaroots varies with soil type and inhibits nitrifying bacteria, but not other major soil microorganisms

Abstract

The tropical pasture grass Brachiaria humidiola (Rendle) Schweick releases nitrification inhibitory compounds from its roots, a phenomenon termed ‘biological nitrification inhibition’ (BNI). We investigated the influence of root exudates of B. humidicola on nitrification, major soil microorganisms and plant growth promoting microorganisms using two contrasting soil types, Andosol and Cambisol. The addition of root exudates (containing BNI activity that is expressed in Allylthiourea unit (ATU) was standardized in a bioassay against a synthetic inhibitor of nitrification, allylthiourea, and their function in soil was compared to inhibition caused by the synthetic nitrification inhibitor dicyandiamide. At 30 and 40 ATU g−1soil, root exudates inhibited nitrification by 95% in fresh Cambisol after 60 days. Nitrification was also similarly inhibited in rhizosphere soils of Cambisol where B. humidicola was grown for 6 months. Root exudates did not inhibit other soil microorganisms, including gram‐negative bacteria, total cultivable bacteria and fluorescent pseudomonads. Root exudates, when added to pure cultures of Nitrosomonas europaea, inhibited their growth, but did not inhibit the growth of several plant growth promoting microorganisms, Azospirillum lipoferum, Rhizobium leguminosarum and Azotobacter chroococcum. Our results indicate that the nitrification inhibitors released by B. humidicola roots inhibited nitrifying bacteria, but did not negatively affect other major soil microorganisms and the effectiveness of the inhibitory effect varied with soil type.

Residual effect of BNI by Brachiaria humidicola pasture on nitrogen recovery and grain yield of subsequent maize

“…Using hydroponic systems, it was claimed that the exudation of BNI substances from roots of Bh is an active release of biological nitrification inhibitors that are triggered by the presence of NH 4 + (Subbarao et al 2007b). These Bh exudates contained BNI active substances like methyl-p-coumarate and methyl ferulate, while the shoot tissue contained other very effective BNI substances such as linoleic acid (LA) and linolenic (LN) acid (Gopalakrishnan et al 2009). Additionally, the cyclic diterpene brachialactone was suggested to be the main substance in root exudates of Bh that suppresses nitrification ).…”

Root extracts of Bracchiaria humidicola andSaccharum spontaneum to increase N use by sugarcane

“…Subbarao et al (2009) were able to isolate an effective nitrification inhibitor (brachialactone) from the root exudates of B. humidicola. Gopalakrishnan et al, (2009) also reported a 29 % reduction in nitrification with an application of 182 mg (NH 4 ) 2 SO 4 -N kg −1 of soil associated with the application of exudates of B. humidicola.…”

“…Root extracts were obtained according to the methodology described by Gopalakrishnan et al, (2009), in which 400 grams of fresh roots of Brachiaria humidicola or Sacharrum spontaneum were washed in running water, set in a container, slightly macerated using a spatula and placed in 2 L of distilled water for 36 h under 20 ºC to transfer the extracts to the solution. Polar metabolites were extracted from 100 µL of root extracts of Brachiaria humidicola and Sacharrum spontaneum, using the methodology described by Giavalisco et al, (2011).…”

Biological nitrification inhibition (BNI)-Is there potential for genetic interventions in the Triticeae?

“…BNIs) released from the roots must be stable in the soil environment for several weeks. This was confirmed by adding BNIs to the soil along with NH 4 + as the N source to determine their inhibitory effects on soil nitrification over a 60 d period (Subbarao et al 2006b, Gopalakrishnan et al 2009). …”