The absorption of NH3 by the tomato canopy and the dynamics of this process in the plastic-shed vegetable production systems have not been reported. To quantify the contribution of the leaf absorption of (NH3)-N-15, two field experiments were established to measure the amount of NH3 translocated and recovered cumulatively (Experiment I) and instantaneously (Experiment II) by tomato canopy. Four applications of N-15-labeled urea as side dressing using a plastic tray method to simulate field management conditions. This experimental procedure prevented the uptake of N from the labeled urea by the roots. The results showed that total NH3 loss accounted for 17.9 % of the N applied using the tray method, with average losses of 21.5 % and 14.3 % during the summer and winter growing seasons, respectively. The average canopy absorption of volatilized (NH3)-N-15 was 12.2 % of the total N applied and the average canopy absorption rate of (NH3)-N-15 reached to 2.81 % of the total N-15-urea applied. Additionally, an average of 44.13 % of the absorbed (NH3)-N-15-N was transferred into the tomato fruit. Across four growth stages, whole-plant N-15 accumulation increased gradually over the first three stages, with peak absorption occurring during the topping and pruning stage. Then, absorption rates decreased significantly during harvesting. NH3 uptake by the tomato canopy was significantly more dynamic in summer than in winter. Our findings shed significant light on how NH3 is taken up by the greenhouse tomato canopy and can contribute to improving the sustainability of agricultural systems.
