Biological nitrification inhibition by root exudates of native species,Hibiscus splendensandSolanum echinatum

Abstract

Australian native species grow competitively in nutrient limited environments, particularly in nitrogen (N) limited soils; however, the mechanism that enables this is poorly understood. Biological nitrification inhibition (BNI), which is the release of root exudates into the plant rhizosphere to inhibit the nitrification process, is a hypothesized adaptive mechanism for maximizing N uptake. To date, few studies have investigated the temporal pattern and components of root exudates by Australian native plant species for BNI. This study examined root exudates from two Australian native species, Hibiscus splendens and Solanum echinatum, and contrasted with exudates of Sorghum bicolor, a plant widely demonstrated to exhibit BNI capacity. Root exudates were collected from plants at two, four, and six weeks after transplanting to solution culture. Root exudates contained three types of organic acids (OAs), oxalic, citric and succinic acids, regardless of the species. However, the two Australian natives species released larger amount of OAs in earlier development stages than S. bicolor. The total quantity of these OAs released per unit root dry mass was also seven-ten times greater for Australian native plant species compared to S. bicolor. The root exudates significantly inhibited nitrification activity over six weeks’ growth in a potential nitrification assay, with S. echinatum (ca. 81% inhibition) > S. bicolor (ca. 80% inhibition) > H. splendens (ca. 78% inhibition). The narrow range of BNI capacity in the study plants limited the determination of a relationship between OAs and BNI; however, a lack of correlation between individual OAs and inhibition of nitrification suggests OAs may not directly contribute to BNI. These results indicate that Australian native species generate a strongly N conserving environment within the rhizosphere up to six weeks after germination, establishing a competitive advantage in severely N limited environments.

Ammonia-oxidizing bacterial communities are affected by nitrogen fertilization and grass species in native C4 grassland soils

“…However, there was a negative correlation between DOC and amoA transcript abundance in our study, which was also observed in estuarine ecosystems ( Happel et al, 2019 ). Many studies have observed that nitrification rates can be inhibited by increased organic C concentration in terrestrial ecosystems due to (1) biological nitrification inhibition ( Elroy & Sunil, 1973 ; Janke, Wendling & Fujinuma, 2018 ; Subbarao et al, 2009 ; White, 1986 ); (2) phenolics, tannins, and monoterpenes promoting heterotrophic immobilization of ammonium and decreasing substrate availability for nitrifiers ( Bremner & McCarty, 1993 ; Paavolainen, Kitunen & Smolander, 1998 ); and (3) the increased competition between heterotrophic and nitrifying bacteria for ammonium caused by high quality C ( i.e., labile carbon) ( Strauss & Lamberti, 2002 ).…”

Intra‐ and inter‐annual variability of nitrification in the rhizosphere of field‐grown bioenergy sorghum

“…The expanding body of literature on BNI suggests that many plant species may be capable of reducing nitrification in the rhizosphere (Chowdhury et al, 2017;Coskun et al, 2017a;Janke et al, 2018;Subbarao et al, 2007). In the agricultural setting, direct and indirect suppression of nitrification could reduce NO 3 − losses from annual cropping systems, with the agronomic benefit of increased fertilizer use efficiency and environmental benefits of reduced NO 3 − flow into downstream waterways and N 2 O emissions into the atmosphere.…”

Sedimentary Organic Matter Load Influences the Ecological Effects and Potential Risks of Submerged Macrophyte Restoration Through Rhizosphere Metabolites

“…A suitable sediment NH 4 -N range for V. natans has been reported as 5-50 mg/kg (Zhu et al, 2006). Although only a few nitri cation inhibition agents from root exudates have been identi ed, BNI activity was con rmed in different plant species, blocking either the ammonia monooxygenase (AMO) pathway or both the AMO and hydroxylamine oxidoreductase (HAO) pathways (Sun et al, 2016, Janke et al, 2018. BNI function is thought to be triggered by the synergistic effect of NH 4 -N presence and low pH in the root environment (Subbarao et al, 2007).…”