Local plant responses to global problems: Dactylis glomerata responses to different traffic pollutants on roadsides.

The growing number of road vehicles is a major source of regional and global atmospheric pollution increasing concentrations of CO2 in the air, and levels of metals in air and soil. Nevertheless, the effects of these pollutants on plants growing at roadsides are poorly documented. We carried out an observational study of unmanipulated plants growing by the road, to identify the morpho-physiological responses in a perennial grass Dactylis glomerata. Firstly, we wanted to know the general effect of traffic intensity and ambient CO2 and its interactions on different plant traits. Accordingly, we analyzed the photosynthetic response by field A/Ci Response Curves, SLA, pigment pools, foliar nitrogen, carbohydrates and morphological traits in plants at three distances to the road. Secondly, we wanted to know if Dactylis glomerata plants can accumulate metals present on the roadside (Pb, Zn, Cu, and Sr) in their tissues and rhizosphere, and the effect of these metals on morphological traits. The MANCOVA whole model results shown: 1) a significant effect of road ambient CO2 concentration on morphological traits (not affected by traffic intensity, P interaction CO2 x traffic intensity >0.05), that was mainly driven by a significant negative relationship between the inflorescence number and ambient CO2 ; 2) a positive and significant relationship between ambient CO2 and the starch content in leaves (unaffected by traffic intensity); 3) a reduction in Jmax (electron transport rate) at high traffic intensity. These lines of evidences suggest a decreased photosynthetic capacity due to high traffic intensity and high levels of ambient CO2 . In addition, Pb, Cu, Zn and Sr were detected in Dactylis glomerata tissues, and Cu accumulated in roots. Finally, we observed that Dactylis glomerata individuals growing at the roadside under high levels of CO2 and in the presence of metal pollutants, reduced their production of inflorescences.