Browsing by Subject "Ammonia oxidizing archaea (AOA)"

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Abundance and diversity of total and nitrifying prokaryotes as influenced by biochemical quality of organic inputs, mineral nitrogen fertilizer and soil texture in tropical agro-ecosystems
(2016) Muema, Esther Kathini; Cadisch, Georg
Tropical agro-ecosystems are limited in nutrient resources as a consequence of i) being composed of highly weathered soils, ii) low native soil organic matter (SOM) content due to conversion of natural forests to arable lands and iii) continuous cropping without replenishing soil nutrients. Recovery of SOM by use of organic residues is faced with other competing uses like animal fodder. Moreover, existing SOM is further reduced by increased turnover rates due to favorable climatic conditions in the tropics. Incorporation of residues is therefore a justified means to restore SOM and to provide crop nutrients through microbial mediated activities like nitrification. Nitrification is a central step of the nitrogen (N) cycle, whereby ammonia is converted into nitrite and then to nitrate by bacteria and archaea through production of the amoA gene encoding the alpha-subunit of the enzyme ammonia monooxygenase. In order to better understand the impact of organic residues of contrasting biochemical quality (i.e., high quality Tithonia diversifolia (TD; C/N ratio: 13, lignin: 8.9 %, polyphenols: 1.7 %), intermediate quality Calliandra calothyrsus (CC; 13, 13, 9.4) and low quality Zea mays (ZM; 59, 5.4, 1.2)) on nutrient provision, effects of residue quality on dynamics of relevant decomposer microbial communities were studied. In addition, mineral N fertilizer was used to compensate for mineral N limitations especially in case of low and intermediate quality residues. Since N is one of the most limiting crop nutrients in the tropics, this study therefore focused on ammonia-oxidizing prokaryotes, using DNA-based quantitative PCR (qPCR) and terminal restriction fragment length polymorphism (TRFLP) techniques. In addition, soil physicochemical properties were measured and linked to the dynamics of microbial communities. The study hypothesized that soil type due to differences in structure and nutrient background, as well as seasonality, which influences soil moisture, would shape the response of the studied communities to biochemical quality of residues. Overall, the results of this PhD research revealed specific responses of dynamics of AOB and AOA to quality of organic residues and their combinations with mineral N fertilizer. They also revealed effects of interrelations between quality of residues and soil texture as well as seasonality particularly precipitation on dynamics of microbial communities. Future investigation of active microbial communities with the use of RNA-based approaches need to be considered to further improve our understanding of quality of SOM on soil nutrient dynamics.
Inter-microbial competition for N and plant NO3− uptake rather than BNI determines soil net nitrification under intensively managed Brachiaria humidicola
(2021) Egenolf, Konrad; Schad, Philipp; Arevalo, Ashly; Villegas, Daniel; Arango, Jacobo; Karwat, Hannes; Cadisch, Georg; Rasche, Frank
Brachiaria humidicola (syn. Urochloa humidicola) has been acknowledged to control soil nitrification through release of nitrification inhibitors (NI), a phenomenon conceptualized as biological nitrification inhibition (BNI). Liming and N fertilization as features of agricultural intensification may suppress BNI performance, due to a decrease in NI exudation, increased NH3 availability and promotion of ammonia oxidizing bacteria (AOB) over archaea (AOA). A 2-year three-factorial pot trial was conducted to investigate the influence of soil pH and soil microbial background (ratio of archaea to bacteria) on BNI performance of B. humidicola. The study verified the capacity of B. humidicola to reduce net nitrification rates by 50 to 85% compared to the non-planted control, irrespective of soil pH and microbial background. The reduction of net nitrification, however, was largely dependent on microbial N immobilization and efficient plant N uptake. A reduction of gross nitrification could not be confirmed for the AOA dominated soil, but possibly contributed to reduced net nitrification rates in the AOB-dominated soil. However, this putative reduction of gross nitrification was attributed to plant-facilitated inter-microbial competition between bacterial heterotrophs and nitrifiers rather than BNI. It was concluded that BNI may play a dominant role in extensive B. humidicola pasture systems, while N immobilization and efficient plant N uptake may display the dominant factors controlling net nitrification rates under intensively managed B. humidicola.
Metabolome fingerprinting reveals the presence of multiple nitrification inhibitors in biomass and root exudates of Thinopyrum intermedium
(2024) Issifu, Sulemana; Acharya, Prashamsha; Schöne, Jochen; Kaur-Bhambra, Jasmeet; Gubry-Rangin, Cecile; Rasche, Frank
Biological Nitrification Inhibition (BNI) encompasses primarily NH4 +-induced release of secondary metabolites to impede the rhizospheric nitrifying microbes from per- forming nitrification. The intermediate wheatgrass Thinopyrum intermedium (Kernza®) is known for exuding several nitrification inhibition traits, but its BNI potential has not yet been identified. We hypothesized Kernza® to evince BNI potential through the presence and release of multiple BNI metabolites. The presence of BNI metabolites in the biomass of Kernza® and annual winter wheat (Triticum aestivum) and in the root exudates of hydroponically grown Kernza®, were fingerprinted using HPLC-DAD and GC–MS/MS analyses. Growth bioassays involving ammonia-oxidizing bacteria (AOB) and archaea (AOA) strains were conducted to assess the influence of the crude root metabolome of Kernza® and selected metabolites on nitrification. In most instances, significant concentrations of various metabolites with BNI potential were observed in the leaf and root biomass of Kernza® compared to annual winter wheat. Furthermore, NH4 + nutrition triggered the exudation of various phenolic BNI metabolites. Crude root exudates of Kernza® inhibited multiple AOB strains and completely inhibited N. viennensis. Vanillic acid, caffeic acid, vanillin, and phenylalanine suppressed the growth of all AOB and AOA strains tested, and reduced soil nitrification, while syringic acid and 2,6-dihydroxybenzoic acid were ineffective. We demonstrated the considerable role of the Kernza® metabolome in suppressing nitrification through active exudation of multiple nitrification inhibitors.