Further insights into underlying mechanisms for the release of biological nitrification inhibitors from sorghum roots

Abstract

Background Sorghum roots release two categories of biological nitrification inhibitors (BNIs)hydrophilic-BNIs and hydrophobic-BNIs. Earlier research indicated that rhizosphere pH and plasma membrane (PM) H + ATPase are functionally linked with the release of hydrophilic BNIs, but the underlying mechanisms are not fully elucidated. This study is designed to reveal further insights into the regulatory mechanisms of BNIs release in root systems, using three sorghum genetic stocks. Methods Sorghum plants were grown in a hydroponic system with pH of nutrient solutions ranging from 3.0 9.0. Pharmacological agents [(fusicoccin and vanadate) and anion-channel blockers (−niflumic acid (NIF) and

Rhizosphere pH and cation‐anion balance determine the exudation of nitrification inhibitor 3‐epi‐brachialactone suggesting release via secondary transport

“…One acknowledged mechanism is the stimulation of NI release by low rhizosphere pH and NH 4 + nutrition, as was proven in hydroponic experiments. This has been described for brachialactone in B. humidicola (Subbarao et al, 2009;, polar NIs released by S. bicolor (Di et al, 2018),…”

“…One acknowledged mechanism is the stimulation of NI release by low rhizosphere pH and NH 4 + nutrition, as was proven in hydroponic experiments. This has been described for brachialactone in B. humidicola (Subbarao et al, 2009; Subbarao, Wang, et al, 2007), polar NIs released by S. bicolor (Di et al, 2018), unidentified NIs from L. racemosus (Subbarao, Wang, et al, 2007) and to a certain extent also for 1,9‐decandiol in O. sativa (Pariasca Tanaka et al, 2010). These results were perceived as evidence for NIs being secreted via a regulated process, e.g.…”

“…S. bicolor , L. racemosus , O. sativa ). Especially for the polar NI fraction in S. bicolor , pH and N form determined NI release (Di et al, 2018). Moreover, the NI release correlated strongly with PM‐H + ATPase (Zhu et al, 2012), a scenario taken as evidence for exudation via MATE transporters in various plant species (Kochian et al, 2015; Magalhaes et al, 2018; Zhang et al, 2017).…”

“…Furthermore, exudation is considered as regulated if the plant controls the release rate and directly responds to ecological triggers. In the case of S. bicolor, Di et al (2018) -Pizarro et al, 2014;Schubert & Yan, 1997). Furthermore, the subsequent signal cascade and the proposed NI channels remain merely speculative.…”

“…Furthermore, exudation is considered as regulated if the plant controls the release rate and directly responds to ecological triggers. In the case of S. bicolor , Di et al (2018) explained the stimulating effect of NH 4 + on NI release by a signaling cascade, where NH 4 + uptake leads to an increase in plasmalemma (PM) H + ATPase activity triggering the opening of anion channels, which is finally responsible for NI release. This theory thus suggests a regulated, facilitated passive transport as release pathway.…”