Nitrogen utilization and metabolism in maize (Zea mays L.) plants under different rates of biochar addition and nitrogen input conditions.

Biochar (BC) application could improve plant nitrogen (N) utilization and potentially reduce N fertilizer requirements. However, the fate of N in crop-soil systems and the metabolic responses of crops under the condition of BC coapplied with reduced N are not well understood. The urea-15 N isotope and pot experiments with three BC rates (0%, 5% and 15%; w/w) combined with three N fertilizer levels (100%-N, 85%-N and 55%-N) were conducted for maize. The metabolome, 15 N abundance and gene expression in plants were analyzed using nuclear magnetic resonance, gas isotope mass and quantitative real-time reverse transcription-PCR, respectively. The results showed that the recovery of N by maize ranged from 27.4% to 23.6% and decreased as the N application rate decreased (from 100% to 55%) without BC addition, ranged from 24.6% to 29.4% when BC was added at a rate of 5% and increased as the N application rate decreased. BC addition had major effects on global metabolic profiles and metabolic networks at the metabolomics level as well as on the expression of related genes (zmGS1and zmAS1) and the contents of mineral N (NO3 - -N, NO2 - -N and NH4 + -N) in the maize seedlings; however, the interaction effects of the BC application rates and N fertilizer levels were evident (p ≤ 0.001). BC addition induced a decrease in the flux toward sugar hydrolysis and remained a homeostasis in the amino acid pool, which was perturbed by reduced N levels; then, the maize plants adapted to the reduced-N condition, and the N recovery efficiency was ultimately improved with reduced N loss. This article is protected by copyright. All rights reserved.