Evidence of biological nitrification inhibition in barley to support sustainable nitrogen management.

Nitrification drives nitrogen loss in agricultural systems, resulting in leached nitrate and increased emissions of the greenhouse gas nitrous oxide, thereby reducing nitrogen use efficiency (NUE). Biological nitrification inhibition (BNI) provides a promising nature-based solution to low-NUE by suppressing nitrifying microorganisms via plant-exuded bioactive metabolites. Although BNI is well documented in several major cereal grasses, evidence of BNI in barley (Hordeum vulgare) is lacking. This study demonstrates barley BNI activity through suppression of rhizosphere ammonia-oxidizer abundance, without a corresponding inhibition of the total prokaryotic community. Several barley lines exhibited strong inhibition of rhizosphere ammonia oxidizers consistent with high-BNI efficiency. The impact of BNI on the rhizosphere microbial community revealed clear differential effects across multiple phylogenetic clades of ammonia oxidizers, revealing that nitrifier clades differ in sensitivity to BNI in the rhizosphere. This led to a decrease in ammonia-oxidizer community richness correlating with BNI activity. The selective inhibition of rhizosphere ammonia oxidizers suggests that further research across diverse soils is needed. This study clearly demonstrates barley BNI activity in soil through suppression of rhizosphere ammonia oxidizers, identifying promising high-BNI lines, and providing a foundation for developing high-BNI barley cultivars to enhance NUE and increase agricultural sustainability.