Abstract Description

Nitrogen (N) transformations in agricultural soils are primarily governed by microbial processes, which include mineralisation, nitrification, and denitrification. These factors collectively determine N availability and losses. One of the mechanisms used by farmers to add N to the soil is the use of inorganic fertilisers. However, excessive N fertilisation results in soil microbial community disruption, therefore leading to diminished nitrogen use efficiency (NUE). Furthermore, N is lost environmentally through leaching and greenhouse gas emissions. Retaining N in the soil is essential for sustainable crop production. Wheat (Triticum aestivum L. and Triticum turgidum subsp. durum), a key staple crop for South Africa, faces challenges such as declining domestic yields. Improving NUE through the selection and genetic improvement of wheat genotypes with superior N cycling abilities is critical for enhancing productivity and sustainability. The study aims to evaluate the influence of different wheat genotypes and varying N application rates on soil nitrification rates. A field trial with 20 wheat genotypes was conducted under uniform conditions with controlled N inputs. Rhizosphere soils were analysed for microbial composition using 16S rRNA amplicon sequencing, and potential nitrification rate (PNR) was measured with a nitrate-selective probe. Historic genotypes with diverse root traits were included to assess their influence on N uptake and microbial interactions. Several historic genotypes exhibited significantly lower PNR compared to modern genotypes after N application at the heading stage. Modern genotypes showed suppression of key nitrifying microbial groups. Metabolic function predictions suggested higher N availability for plants and lower microbial N consumption in historic genotypes rhizospheres. Overall, genetic variation in wheat root traits shaped rhizosphere microbial activity and nitrification rates, with historic genotypes showing greater potential to retain N in soils. These interactions highlight the importance of managing plant–microbe relationships to enhance NUE, maintain soil health, and reduce environmental losses. Strengthening plant-microbe interactions can therefore support more sustainable wheat production.