Abstract
Soil nitrification (microbial oxidation of ammonium to nitrate) can lead to nitrogen leaching and environmental pollution. A number of plant species are able to suppress soil nitrifiers by exuding inhibitors from roots, a process called biological nitrification inhibition (BNI). However, the BNI activity of perennial grasses in the nutrient-poor soils of Australia and the effects of BNI activity on nitrifying microbes in the rhizosphere microbiome have not been well studied. Here we evaluated the BNI capacity of bermudagrass (Cynodon dactylon L.), St. Augustinegrass (Stenotaphrum secundatum (Walt.) Kuntze), saltwater couch (Sporobolus virginicus), seashore paspalum (Paspalum vaginatum Swartz.), and kikuyu grass (Pennisetum clandestinum) compared with the known positive control, koronivia grass (Brachiaria humidicola). The microbial communities were analysed by sequencing 16S rRNA genes. St. Augustinegrass and bermudagrass showed high BNI activity, about 80 to 90% of koronivia grass. All the three grasses with stronger BNI capacities suppressed the populations of Nitrospira in the rhizosphere, a bacteria genus with a nitrite-oxidizing function, but not all of the potential ammonia-oxidizing archaea. The rhizosphere of saltwater couch and seashore paspalum exerted a weak recruitment effect on the soil microbiome. Our results demonstrate that BNI activity of perennial grasses played a vital role in modulating nitrification-associated microbial populations.
Highlights
The application of N fertiliser is the most important nutritional component of the modern agricultural system following the Green Revolution but can lead to large environmental costs [1]
After the initial discovery in koronivia grass (Brachiaria humidicola) [4], biological nitrification inhibition (BNI) activity has been widely found in other forage grasses (e.g., Brachiaria decumbens [5] and Hyparrhenia diplandra [6]), major cereal crops (e.g., sorghum (Sorghum bicolor) [7] and rice (Oryza sativa) [8]), and agricultural weed species such as Lolium rigidum, Bromus driandrus, Raphinus raphinastrum, and Avena fatua [9]
Augustinegrass cultivar “Sir Walter”; native saltwater couch collected from South Australia (36.335◦ S, 139.754◦ E); native seashore paspalum collected from South Australia (35.544◦ S, 138.630◦ E); kikuyu grass cultivar “Whittet”; koronivia grass cultivar “Tully” sourced from the Australian Pastures Genebank
Summary
The application of N fertiliser is the most important nutritional component of the modern agricultural system following the Green Revolution but can lead to large environmental costs [1]. Nitrification is the microbial oxidation of the relatively immobile ammonium-N (NH4+) to highly mobile nitrate (NO3−) via NH4+ → NH2OH → NO2− → NO3− which increases N leaching of NO3− in soils [3]. After the initial discovery in koronivia grass (Brachiaria humidicola) [4], BNI activity has been widely found in other forage grasses (e.g., Brachiaria decumbens [5] and Hyparrhenia diplandra [6]), major cereal crops (e.g., sorghum (Sorghum bicolor) [7] and rice (Oryza sativa) [8]), and agricultural weed species such as Lolium rigidum, Bromus driandrus, Raphinus raphinastrum, and Avena fatua [9]. Genotypic variation in BNI within the same plant species has been detected in wheat landraces and cultivars [10], and B. humidicola populations [11]
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