Phytoavailability and speciation of aluminum carried by total suspended particulates (TSP) to Masson pine (Pinus massoniana L.)

Abstract Aluminum (Al) is an abundant metal in airborne particulate matter. Al concentrations carried by total suspended particulates (TSP) of the Nanjing atmosphere were distinctly higher in soils of industrial areas than the background concentration of the soils. This study aimed to assess the influence of the soils varying in their degree of contamination on the soil-to-plant transfer and translocation of Al to Masson pine ( Pinus massoniana L.). A pot experiment was conducted to investigate the phytoavailability and speciation of Al carried by TSP which was collected at urban and industrial sites over a 12-month period in the atmosphere of Nanjing, China. The extractable noncrystalline Al in environmental particulate samples could be operationally fractionated into insoluble (Alin), oxide (Alox), organic (Alor), carbonate (Alca), and exchangeable species (Alex) using Tessier's sequential extraction procedure. The results showed that relatively high Al concentrations in TSP and soil samples were observed at the industrial site due to emissions from a local industry that manufactures Al-based products. The distribution sequence of Al species was quite similar for TSP and soil samples, which was Alin > Alor > Alox > Alca > Alex. The order of industrial particulate matter (IPM) was Alin > Alox > Alca > Alex > Alor. Alor was not detectable. A greater migration of Alex species entered the pine roots and the highest Al contents were accumulated in the roots and declined in the aerial portions. The soil-to-pine Al transfer was extremely low even when grown on industrial Al-contaminated soils. A significant positive correlation was found between the Al contents in pine seedlings and rhizospheric Alex contents. In contrast, there was a strong negative correlation between rhizospheric Alex contents and seedling biomass. For the spiked soils, under the influence of IPM, Al phytoavailability decreased with elevated rhizospheric Al and Alex. Collectively, this study provided evidence of Alex and Alor species dependent Al phytoavailability. Excessive Al carried by IPM lead to a decline in the pine biomass production, and different Al phytoavailabilities showed differentiated responses to IPM addition.