High nitrogen addition decreases the ozone flux by reducing the maximum stomatal conductance in poplar saplings

Ground-level ozone (O-3) and nitrogen (N) deposition are major environmental pollutants, often occurring concurrently. Ozone exposure- and flux-response relationships for tree biomass are used for regional O-3 risk assessment. In order to investigate whether soil N addition affects stomatal O-3 uptake of poplar, poplar saplings were exposed to treatment combinations of five O-3 levels and four N addition levels. High N addition treatment reduced the accumulated stomatal O-3 uptake in the leaf due to reduced maximum stomatal conductance (g(s)). Nitrogen addition also significantly reduced the steady-state light-saturated gs in August and September. Elevated O-3 significantly reduced and N addition increased total plant biomass; however, there were no significant O-3 x N interactions. The slopes of biomass-based O-3 exposure- and flux-response relationships did not differ significantly among N treatments. The critical levels for a 5% biomass reduction were estimated at 15.4 ppm h and 17.1 mmol O-3 m(-2) projected leaf area (PLA) for Accumulated O-3 exposure Over an hourly Threshold of 40 ppb (AOT40) and Phytotoxic Ozone Dose above a threshold 1 nmol O-3 m(-2) PLA s(-1) (POD1). These results can facilitate the evaluations of O-3 effect on the carbon-sink capacity and productivity of forest. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Ground-level ozone (O-3) and nitrogen (N) deposition are significant environmental pollutants that can affect tree biomass. Studying the impact of N addition on O-3 uptake by poplar saplings revealed that high N addition reduced stomatal O-3 uptake while also decreasing plant biomass. The findings provide insights for evaluating the effects of O-3 on forest carbon-sink capacity and productivity.