Anthropogenic Dusts Influence Leaf Anatomical and Eco-Physiological Traits of Black Locust (Robinia pseudoacacia L.) Growing on Vesuvius Volcano

In the Mediterranean region, some areas of the Vesuvius National Park (southern Italy) are subjected to a severe anthropogenic impact, especially during spring and summer seasons. The continuous trampling of tourists and buses leads to the formation of "dust-clouds", exposing plants, especially along the paths, to a great deposition of powder particles on leaves. The aim of this study was to analyze if the dust deposition induces changes in leaf morpho-anatomical and eco-physiological traits of the alien, invasive, species Robinia pseudoacacia L., with particular attention to the photosystem II (PSII) efficiency. We selected plants located near the paths with a high deposition of dust (HD) and plants far away from the paths (low deposition, LD), and tested them over three dates along summer. We analyzed PSII photochemistry, photosynthetic pigments content, and leaf functional (e.g., relative water content and leaf dry matter content) and morpho-anatomical traits (e.g., parenchyma thickness, mesophyll density). HD plants presented a more efficient PSII activity, indicated by the higher quantum yield of PSII electron transport (FPSII) (9%) and electron transport rate (ETR) (38%) in the end of July. Dust deposition also reversibly altered photosynthetic pigments concentration and some lamina traits, adjustable in the short-term (e.g., intercellular spaces and phenolics distribution). We hypothesize that HD leaves were shielded by dusts which would protect their photosynthetic apparatus from the excess of light.