# Screening of Plants and Indigenous Bacteria to Improve Arsenic Phytoextraction
## 3 Results and Discussion
### Microcosm Tests with Phosphate  
The biomass values from the aerial part of plants grown in the control soils and in the soils treated with KH2 PO4, with or without PGPR bacteria, are shown in Figure 4.  
Of the plant species tested, corn showed the best growth with the highest biomass production. In particular, corn was the only species that managed to grow on PZ soil, albeit with a reduced biomass production compared to that of other soils. The data show that the addition of phosphate and the presence of PGPR bacteria in general favor the growth and biomass production of plant species. The most obvious case occurs for all plants in SW soil. Regarding the absorption of arsenic by plants, the results in Table 3 show rather limited absorption and that even the treatment with phosphate does not bring the concentration of As to such levels as to allow a phytoextraction process to be completed in a short time, although the amount of As absorbed by plants increases. Figure 4: Dry weights (mg pot\({}^{-1}\)) of (**a**) roots and (**b**) shoots of _Z. mays_, _C. sativa_, and _B. junca_ grown on soil control (CT) and As-contaminated soil treated with phosphate (P). The addition of PGPR bacteria (first set of isolates) is indicated with a “+” sign. Values are the mean of three replicates, and the error bars show the standard deviation. Values with different letters are significantly different at the 5% probability level (Tukey’s test). Figure 3: (**a**) Germination index (GI%) and (**b**) root elongation inhibition (Inh%) for _Z. mays_, _C. sativa_, and _B. junca_ grown on soil control (CT) and As-contaminated soil treated with phosphate (P). The addition of PGPR bacteria (first set of isolates) is indicated with a “+” sign. Values are the mean of three replicates, and the error bars show the standard deviation. Values with different letters are significantly different at the 5% probability level (Tukey’s test). After treatment with phosphate (with and without the addition of PGPR bacteria), the absorption of arsenic by corn increased approximately 7 times in soil S2 and approximately 4 times in soils S6 and SW. A certain increase also occurred in the case of PZ soil, characterized as mentioned by a very difficult growth. The treatments also increased the absorption of arsenic by hemp by about 5 times in soils S2 and S6 of the external area and by about 3 times in that of the internal SW area. The addition of PGPR bacteria did not change the amount of arsenic absorbed, although it had a positive effect on biomass production, which generally tends to increase with the addition of PGPR bacteria. Figure 5 provides a comparative evaluation of the phyto-extractive capacity of the different plant species considered. As known, the total amount of removed arsenic is obtained by multiplying its concentration in plant tissues by the biomass produced. Figure 5 also allows an evaluation of the positive effect of phosphate addition for all plant species, highlighting the best results obtained with S2 soil. A positive but not so  
Figure 5: Arsenic uptake by (**a**) roots and (**b**) shoots of _Z. mays_, _C. sativa_, and _B. juncea_ grown on soil control (CT) and As-contaminated soil treated with phosphate (P). The addition of PGPR bacteria (first set of isolates) is indicated with the “+” sign. Values are the mean of three replicates, and the error bars show the standard deviation. Values with different letters are significantly different at the 5% probability level (Tukey’s test).