Microbiome and nitrifying microbes in the rhizosphere of perennial grasses are modified by biological nitrification inhibition

Soil nitrification (microbial oxidation of ammonium to nitrate) can lead to nitrogen leaching and environmental pollutions. A number of plant species are able to suppress soil nitrifiers by exuding inhibitors from roots, a process called biological nitrification inhibition (BNI). However, BNI activity of perennial grasses in nutrient-poor soils of Australia and the effects of BNI activity on 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 bacterial and archaeal communities were analysed by sequencing 16S rRNA genes. St Augustinegrass and bermudagrass showed high BNI activity, about 80% to 90% of BNI activity from koronivia grass. Grasses with stronger BNI capacity suppressed the populations of potential ammonia-oxidizing bacteria in the rhizosphere, 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 bacterial microbiome. Our results demonstrate that BNI activity of perennial grasses played a vital role in modulating the rhizosphere microbiome and nitrification-associated microbial populations.