## 2 Materials and Methods  
### Experimental Design  
A pot trial was carried out at the research area of the University of Agriculture, Faisalabad (UAF) to examine the impact of biochar and _Enterobacter_ sp. MN17 on physiology and growth of mungbean plants in artificially contaminated soil with diesel. The diesel was purchased from Shell petrol filling station, Faisalabad, Pakistan. Clean soil was collected from the research area of UAF and sieved through a 2-mm sieve. Each pot was filled with 8 kg of soil and then pots were placed according to completely randomized design (CRD). The calculated amount of diesel was applied to the pots to get a final concentration of 5000 mg kg\({}^{-1}\) (this concentration was selected on the basis of the results of our initial experiments on PHC phytotoxicity to mungbean germination and growth). Acetone was used as a carrier solvent for spiking. After spiking, the soil was thoroughly mixed and left for one month to enable the biochemical characteristics of the soil and diesel to become stable [29].  
Mungbean (_Vigna radiata_ L.), variety AZRI-2006 was selected as a test plant due to its widespread nature, root morphology, fast growth and adaptation characteristics [27]. The selected pots were amended with 1% biochar (_w/w_) [30]. Previously isolated and identified endophytic bacterium _Enterobacter_ sp. MN17 (deposited in National Center for Biotechnology Information, with accession number KT375575) was obtained from the Laboratory of Soil and Environmental Microbiology, ISES, UAF [31]. The _Enterobacter_ sp. MN17 was grown in Erlenmeyer flask (250 mL) carrying a mineral salt medium (MSM) [32] at 28 \(\pm\) 2 \({}^{\circ}\)C and 180 rpm for 72 h. The culture optical density (OD\({}_{600}\)) was determined using a spectrophotometer (Thermo Electron Corporation, Evolution-300 LC, Warwickshire, UK) and OD\({}_{600}\) was adjusted to 0.5 to get a constant count of bacterial cells (10\({}^{8}\)-10\({}^{9}\) CFU mL\({}^{-1}\)) for use [33]. Mungbean seeds were surface sterilized by soaking them in a 5% NaClO solution for 120 s and then soaked them in 70% C\({}_{2}\)H\({}_{5}\)OH solution for another 120 s, then rinsed them thoroughly with autoclaved distilled water [22]. Mungbean seeds were dipped for 30 min in bacterial culture. While, for controls, seeds were soaked in sterilized MSM for 30 min.  
Six mungbean seeds (treated or un-treated) were sown in the respective pots containing diesel contaminated or uncontaminated soil. After seedling establishment, only three seedlings were maintained in each pot. The suggested amount of N, P, and K fertilizers (i.e., 22.5 kg N ha\({}^{-1}\) as urea, 57.5 kg P ha\({}^{-1}\) as super-phosphate, and 30 kg K ha-1 as sulfate of potash) were applied to each pot [34]. The experiment was performed in triplicate with nine different treatments, including two levels of PHCs (0 and 5000 mg kg\({}^{-1}\)) in different combinations with biochar and _Enterobacter_ MN17, with a total twenty-seven experimental units (see Table S1 for detail). The relative humidity was 67.4% at the start of experiment, and remained in the range of 64.4-65.5% during plant growth till harvesting. All twenty-seven pots were harvested after 90 d. Agronomic and physiological attributes of plants and remaining diesel contents in soil were determined.