Interactive effects of air pollutants and atmospheric moisture stress on aspen growth and photosynthesis along an urban-rural gradient.

Atmospheric pollution could significantly alter tree growth independently and synergistically with meteorological conditions. North China offers a natural experiment for studying how plant growth responds to air pollution under different meteorological conditions, where rapid economic growth has led to severe air pollution and climate changes increase drought stress. Using a single aspen clone (Populus euramericana Neva.) as a 'phytometer', we conducted three experiments to monitor aspen leaf photosynthesis and stem growth during in situ exposure to atmospheric pollutants along the urban-rural gradient around Beijing. We used stepwise model selection to select the best multiple linear model, and we used binned regression to estimate the effects of air pollutants, atmospheric moisture stress and their interactions on aspen leaf photosynthesis and growth. Our results indicated that ozone (O 3) and vapor pressure deficit (VPD) inhibited leaf photosynthesis and stem growth. The interactive effect of O 3 and VPD resulted in a synergistic response: as the concentration of O 3 increased, the negative impact of VPD on leaf photosynthesis and stem growth became more severe. We also found that nitrogen (N) deposition had a positive effect on stem growth, which may have been caused by an increase in canopy N uptake, although this hypothesis needs to be confirmed by further studies. The positive impact of aerosol loading may be due to diffuse radiation fertilization effects. Given the decline in aerosols and N deposition amidst increases in O 3 concentration and drought risk, the negative effects of atmospheric pollution on tree growth may be aggravated in North China. In addition, the interaction between O 3 and VPD may lead to a further reduction in ecosystem productivity. Image 1 • Nitrogen deposition can stimulate aspen growth by increasing canopy nitrogen uptake. • Aerosols can promote aspen growth through diffuse radiation fertilization effects. • Among all pollutants, ozone is the most important factor to inhibit aspen growth. • The effect of VPD on aspen growth is negative and aggravated by ozone pollution. The response of leaf photosynthesis and stem growth to multiple atmospheric pollutants. [ABSTRACT FROM AUTHOR]