Leaf demography and growth analysis to assess the impact of air pollution on plants: A case study on alfalfa exposed to a gradient of sulphur dioxide concentrations

Although air pollution usually leads to a reduction in the overall growth and development of plants, its effects on leaf demography have not been well examined so far. The present study was designed to highlight the capability of the demographic approach, together with traditional growth and other leaf trait analyses, to assess the impact of air pollution on vegetation by exposing plants of Medicago sativa L. (alfalfa) to a long-term gradient of sulphur dioxide (SO2) concentrations (0, 30, 60 and 90 ppb, for 45 consecutive days). This study shows that (i) alfalfa plants tolerated only the lower SO2 concentration, while detrimental effects on leaf demography and growth were imposed by higher SO2 levels, with a less efficient strategy in carbon gain and allocation found in plants under 60 ppb; (ii) leaf demography and traditional growth analysis leaded to agreeing outcomes, but the demographic approach detected the stress induced by SO2 sooner; and more generally (iii) demography can be a powerful and non-destructive tool for monitoring plant responses to air pollution, especially considering that the feasibility of this approach will likely increase with the reduction of its operational time related to the rapid expansion of several automated phenotyping techniques.