Effect of zinc-solubilizing bacteria and waste tire rubber powder on the growth and Zn and Fe concentrations of corn plant

Waste tire rubber (WTR) contain significant amounts of zinc ‌(Zn) and they are potential sources of Zn for plants. This study was carried out to investigate the effect of Zn-dissolving Pseudomonas isolates and WTR on growth characteristics and Zn and Fe concentrations of the corn plant. An experiment was conducted in a completely randomized design with factorial arrangement with three replications in a sterile sand‌-culture in green house condition. The experimental factors include Pseudomonas bacteria at six levels (without inoculation (C) and inoculation with five isolates (B1 to B5)) and Zn treatment from the WTR source at four levels of 0 (C), 100 (T1), 200 (T2) and‌ 300 (T3) mg Zn per kg‌ (equivalent to 0, 9, 18 and‌ 27‌ g WTR per kg of sand respectively). The results showed that the main effects of the treatments on Photosynthetic performance index, chlorophyll content of leaves, Chlorophyll fluorescence and shoot dry weight were significant. The amount of each of these parameters increased in all bacterial and WTR treatments. The use of WTR (18 g/kg) along with inoculation of isolates increased all measured parameters compared to the control. Root dry weight and zinc concentration in shoots and roots, were affected by the interaction of treatments. The highest amount of plant dry weight was observed in B3+T3 treatment (2.14 fold increase compared to the control (. The concentration of zinc in the plant shoots was the highest in the B4+T3 treatment, which was 20 times higher than the control. The highest concentration of zinc in the root was observed in the presence of isolates B3‌ and ‌B2 in WTR (18 g/kg) treatment which was 25 ‌and ‌22 times higher than the control, respectively. The highest concentration of iron in the shoots and roots of the plant was related to the WTR (18 g/kg) treatment with the amount of 28.3 and 30.7 mg kg-1, respectively. The bacterial isolates increased the iron concentration of shoot compared to the control, but no significant difference was observed between the isolates.