Heavy metal accumulation in leaves affects physiological performance and litter quality of Quercus ilex L.

This study aimed to investigate the relationships between leaf functional modifications and heavy metal concentrations of Quercus ilex L., a good bioindicator of air quality. In addition, as metal concentration in litter plays an important role in decomposition and, in turn, in biogeochemical cycles, samples of undecomposed and whole-leaf litter were analyzed for heavy metals. Leaves and leaf litter of Q. ilex were collected at six sites (roadsides, motorway sites, and urban parks) in Naples (Southern Italy) and characterized for Cd, Cr, Cu, Ni, and Pb concentrations. The investigated functional leaf traits were: leaf area (LA), specific leaf area (SLA), leaf dry-matter content (LDMC), water content (WC), leaf relative water content (RWC), maximal PSII photochemical efficiency (F-v/F-m, variable fluorescence / maximal fluorescence), and total chlorophyll concentration. The motorways were the most contaminated sites, and Pb was the main responsible source of contamination. The metal contamination caused slight variation of F-v/F-m, suggesting that metals did not significantly alter functionality of the photosynthetic apparatus. On the other hand, it can be supposed that higher leaf deposit can cause an increase of pigment biosynthesis in response to the shading increase caused by dust deposition.