Inoculation of endophytic bacteria has been accepted as a promising technique to assist phytostabilization of heavy metal-contaminated soils. This study investigated the effects of inoculating a bacterial strain closely related to Pseudomonas pyschrophila on the plant growth, and phytostabilization of fast-growing trees Acacia mangium and Eucalyptus camaldulensis, growing on artificial spiked soil with Pb up to 1500 mg/kg. After 60 days, the results showed that the strain closely related to P. pyschrophila slightly increased Pb bioavailability and Pb uptake by A. mangium, compared to non-inoculated controls. It slightly reduced Pb bioavailability in soil, but it did not affect the Pb uptake by E. camaldulensis, compared to non-inoculated controls. Interestingly, it was able to significantly increase Pb content in shoots by 3.07-fold in A. mangium and 2.95-fold in E. camaldulensis, compared to non-inoculated controls. Although the inoculation of the strain closely related to P. pyschrophila slightly increased the translocation factor (TF) of Pb in both tree species, their TF values were less than 1. This indicates that plants associated with the strain closely related to P. pyschrophila are suitable for phytostabilization of A. mangium, which may be used for cleaning up Pb contaminated sites. This strain displayed different influences on plant species and was found not suitable for phytostabilization of E. camaldulensis.

Tree species (including Eucalyptus camaldulensis, Ziziphus spina-christi, Albizia lebbeck, Prosopis juliflora, Pithecellobium dulce, and Ficus altissima) were investigated to elucidate their appropriates for green belt application. Leaf samples were collected from four different locations in Riyadh: (1) residential; (2) dense traffic; (3) industrial; and (4) reference sites located approximately 20 km away from the city of Riyadh. Leaves collected from the industrial site showed the highest leaf area reduction. The smallest reduction of leaf areas was observed for F. altissima (11.6%), while the highest reduction was observed for P. juliflora (34.8%). Variations in the air pollution tolerance index (APTI) coupled with the anticipated performance index (API) for each species were examined. The APTI value of Z. spina-christi was highest (58.5) at the industrial site while the lowest APTI value was for P. juliflora (14) at the reference site. Correlation coefficient and linear regression analyses determined that the correlation between the ascorbic acid content and APTI is positive and significantly strong. Our findings indicate that urban green planning in Riyadh should include growing F. altissima on roadsides as well as in heavy industrial locations followed by Z. spina-christi and A. lebbeck according to their API and APTI performances.