Organic farming promotes selective uptake of glycine over nitrate uptake by pakchoi

Understanding how plants use of various nitrogen (N) sources is important for improving plant N use efficiency in organic farming systems. This study investigated the effects of farming management practices (organic and conventional) on pakchoi short-term uptake of glycine (Gly), nitrate (NO₃⁻) and ammonium (NH₄⁺) under two N level conditions. Results showed that plant N uptake rates and N contributions from the three N forms in the low N (0.15 μg N g⁻¹ dry soil) treatment did not significantly differ between the organic and conventional soils, except the significantly greater Gly contribution in organic soil at 24 h after tracer addition. Under high N (15 μg N g⁻¹ dry soil) conditions, the N uptake rates, uptake efficiencies, and N contributions of Gly and NH₄⁺-N were significantly greater in pakchoi cultivated in the organic soil compared to conventional soil, whereas the N uptake rates and N contributions from NO₃^–-N decreased in pakchoi cultivated in the organic soil. The greater Gly-N uptake in plants grown in high-N treated organic soil may be related to the greater gross N transformation, Gly turnover rate and the increased expression of an amino acid transporter gene <i>BcLHT1</i>. Intact Gly contributed at most 6% to Gly-derived N at 24 h after tracer additions, which accounting for about 1.24% of the total N uptake in organic soil. Our study suggested that Gly-N and other organic source N might serve as a more important compensatory N source for plants in organic farming.