*3.1. Application of 20-mM Ethanol Improved the Phenotypes and Growth Parameters of Soybean Plants Subjected to Drought Stress*

To confirm whether ethanol could play a pivotal role in overcoming the droughtmediated pernicious impacts on growth attributes, we recorded plant phenotypes, the height of the shoots, shoot DW, root DW, total DW, trifoliate leaf area, and leaf succulence after 8-days of drought imposition (Figure 1A–J). Phenotypic observations indicated that drought stress caused substantial changes, such as yellowing and semi-drying of leaves in

'D' plants, compared with 'WW' plants (Figure 1A–C). On the other hand, 'Eth + D' plants displayed a noteworthy improvement in phenotypic appearance when compared with that of 'D' plants (Figure 1A–C). Shoot height was substantially reduced in 'D' plants relative to 'WW' plants, whereas external application of ethanol improved shoot height in 'Eth + D' plants when contrasted with 'D' plants (Figure 1D,J). Likewise, drought stress markedly reduced shoot DW, root DW, and total DW in 'D' plants relative to 'WW' plants, while ethanol application significantly improved all these DW parameters in 'Eth + D' plants in comparison with 'D' plants (Figure 1E–G,J). Similarly, relative to 'WW' plants, a conspicuous reduction in leaf area and leaf succulence was observed in 'D' plants (Figure 1H–J). On the other hand, ethanol application substantially improved leaf area and leaf succulence in 'Eth + D' plants when contrasted with 'D' plants (Figure 1H–J).

**Figure 1.** Effect of exogenously supplied 20-mM ethanol on soybean plants exposed to 8 days of water-withholding-induced drought stress. Photographs of soybean plants were taken before (**A**) and after (**B**) exposure to drought stress. (**C**) Close-up photographs of representative soybean leaves (first trifoliate from the bottom of the plant) from each treatment. (**D**) Shoot height, (**E**) shoot DW, (**F**) root DW, (**G**) total DW, (**H**) total leaf area per trifoliate, and (**I**) leaf succulence of soybean plants under different treatments. (**J**) Heatmap of the fold-change values of the aforementioned morphological parameters in soybean plants under different treatments. Bars represent means with standard errors (*n* = 4). Different letters shown above the bars are used to indicate significant differences among the treatments (*p* < 0.05). WW, Eth, D, and Eth + D indicate water-sprayed well-watered plants, ethanol-sprayed well-watered plants, water-sprayed drought-exposed plants, and ethanol-sprayed drought-exposed plants, respectively. DW, dry weight; FW, fresh weight.

#### *3.2. Ethanol Improved Gas Exchange Parameters of Soybean Plants Subjected to Drought Stress*

*Pn*, *gs*, *E*, LT, WUEint, and WUEins were determined to assess whether ethanol has any role in modulating gas exchange parameters under drought stress (Figure 2A–G). We observed that drought stress caused a significant reduction in *Pn*, *gs*, and *E*, and an increase in LT, WUEint, and WUEins in 'D' plants when compared with those of 'WW' plants (Figure 2A–G). By contrast, a noteworthy increase in *Pn*, *E*, WUEint, and WUEins, and a decrease in LT were observed in 'Eth + D' plants, relative to 'D' plants (Figure 2A,C–G). Nonetheless, 'Eth' plants displayed a substantial improvement in *Pn*, *gs*, and *E*, and a decrease in LT compared with 'WW' plants (Figure 2A–D,G).

**Figure 2.** Effect of exogenously supplied 20-mM ethanol on (**A**) photosynthetic rate (*Pn*), (**B**) stomatal conductance to H2O (*gs*), (**C**) transpiration rate (*E*), (**D**) leaf temperature (LT), (**E**) intrinsic WUE (WUEint), and (**F**) instantaneous WUE (WUEins) of soybean leaves subjected to drought stress for a period of 8 days. (**G**) Heatmap of the fold-change values of the aforementioned parameters in soybean plants under different treatments. Bars represent means with standard errors (*n* = 4). Different letters shown above the bars are used to indicate significant differences among the treatments (*p* < 0.05). WW, Eth, D, and Eth + D indicate water-sprayed well-watered plants, ethanol-sprayed well-watered plants, water-sprayed drought-exposed plants, and ethanol-sprayed drought-exposed plants, respectively. WUE, water-use-efficiency.
