3.1.1. Waterlogging Stress and Wheat Growth during the Study

The waterlogging stress was applied up to the overwintering stage; initially, stress did not affect plant growth significantly (*p* ≤ 0.05). It was evident in the change of florescence value and photosynthetic rate (Figure 1a,b), which were 0.794 and 14.58 μmol CO2 m−<sup>2</sup> s<sup>−</sup>1, respectively, at the start of the experiment. At the flowering stage, a significant (*p* ≤ 0.05)

change of ~5% was observed in the florescence value, and the photosynthetic rate was decreased by 7%, compared to the control. This was also related to the number of tillers and leaf area of the plants (Figures 2 and 3), which were also significantly (*p* < 0.05) lower than the control. At the flowering stage, the plant had four tillers in the case of stress, while the control had five; the leaf area of the control plant was 1898 cm2, while it was 1330 cm2 in stress conditions. The photosynthetic rate corresponded to the SPAD value, which showed a significant (*p* < 0.05) decrease at the flowering stage (Figure 4). At the flowering stage, it was ~57 in the case of the control and ~50 once waterlogging stress was applied, i.e., a decrease of 10% was observed. The SPAD value is a measure of the chlorophyll value. Both leaf area and photosynthetic rate were negatively affected by stress, consequently reducing total dry matter accumulation rates and final yields. The same trend of fresh and dry biomass was observed in our study, where stress application considerably (*p* ≤ 0.05) reduced the biomass content of the wheat plant (Figures 5 and 6). This significant (*p* ≤ 0.05) decrease in the photosynthetic rate was also correlated with the stomatal conductance (Figure 7b), transpiration rate (Figure 7a), and water use efficiency (Figure 7c). In April 2021, stressed wheat plants showed 9, 10, 8.8, and 9.6% lower stomatal conductance, transpiration rate, intercellular CO2, and water use efficiency, respectively, compared to the control plant.

**Figure 1.** Change in the (**a**) fluorescence and (**b**) photosynthetic activity of the wheat plants from 15 April 2020 to 22 April 2021 (flowering stage) grown under different abiotic stresses. (**c**) The difference in the grain sizes after harvest. Note: reported values are the means and standard deviations of triplicates for each treatment (exact values are given in Table S1). Lowercase letters show the significant differences among treatments according to one-way ANOVA and DMRT, while the significance level was *p* ≤ 0.05. CK: control; WL: waterlogging; SS: salt stress; HS: heat stress; CS: combined stress.

**Figure 2.** Number of tillers during five-stage growth of wheat plants grown under different abiotic stresses. Reported values are the means and standard deviations of triplicates for each treatment. Note: sampling date at overwintering stage was 28 December 2020; at jointing stage was 12 March 2021; at booting stage was 30 March 2021; at the flowering stage was 17 April 2021; and at maturity stage was 28 May 2021. Lowercase letters show the significant differences within treatments according to one-way ANOVA and DMRT, while the significance level was *p* ≤ 0.05.

**Figure 3.** Leaf area of wheat plants during the five-stage plant growth (until flowering stage) grown under different abiotic stresses. Reported values are the means and standard deviations of triplicates for each treatment. Note: sampling date at overwintering stage was 28 December 2020; at jointing stage was 12 March 2021; at booting stage was 30 March 2021; at the flowering stage was 17 April 2021; and at maturity stage was 28 May 2021. Lowercase letters show the significant differences among treatments according to one-way ANOVA and DMRT, while the significance level was *p* ≤ 0.05.

**Figure 4.** SPAD value of wheat plants during the five-stage growth of plants grown under different abiotic stresses. Reported values are the means and standard deviations of triplicates for each treatment. Note: sampling date at overwintering stage was 28 December 2020; at jointing stage was 12 March 2021; at booting stage was 30 March 2021; at the flowering stage was 17 April 2021; and at maturity stage was 28 May 2021. Lowercase letters show the significant differences among treatments according to one-way ANOVA and DMRT, while the significance level was *p* ≤ 0.05.

**Figure 5.** Fresh biomass of wheat plants during five-stage growth of plants grown under different abiotic stresses. Reported values are the means and standard deviations of triplicates for each treatment. Note: sampling date at overwintering stage was 28 December 2020; at jointing stage was 12 March 2021; at booting stage was 30 Mar 2021; at the flowering stage was 17 April 2021; and at maturity stage was 28 May 2021. Lowercase letters show the significant differences within treatments according to one-way ANOVA and DMRT, while the significance level was *p* ≤ 0.05.

**Figure 6.** Dry biomass of wheat plants during the five-stage growth of plants grown under different abiotic stresses. Reported values are the means and standard deviations of triplicates for each treatment. Note: sampling date at overwintering stage was 28 December 2020; at jointing stage was 12 March 2021; at booting stage was 30 Mar 2021; at the flowering stage was 17 April 2021; and at maturity stage was 28 May 2021. Lowercase letters show the significant differences among treatments according to one-way ANOVA and DMRT, while the significance level was *p* ≤ 0.05.

**Figure 7.** (**a**) Transpiration rate; (**b**) stomata conductance; and (**c**) water use efficiency of the wheat plants from 15 April 2020 to 22 April 2021 (flowering stage) grown under different abiotic stresses. Water use efficiency was measured in μmol CO2 m−<sup>2</sup> s−1/mmol H2O m−<sup>2</sup> s−1. Note: Reported values are the means and standard deviations of triplicates for each treatment (exact values are given in Table S1). Lowercase letters show the significant differences among treatments according to one-way ANOVA and DMRT, while the significance level was *p* ≤ 0.05.

#### 3.1.2. Salt Stress and Wheat Growth during the Study

The salt stress was applied after the jointing stage; initially, it was less disturbing for the plant, but the wheat growth was significantly (*p* ≤ 0.05) reduced after the booting stage. It was evident in the change in fluorescence value and photosynthetic rate (Figure 1a,b), which were 0.794 and 14.58 μmol CO2 m−<sup>2</sup> s<sup>−</sup>1, respectively, at the start of the experiment in control. A significant decrease of 2 and 4% was observed in the case of florescence value

and photosynthetic rate, respectively. It was also correlated with the number of tillers. Tillers and leaf area of the plant (Figures 2 and 3) were 6.8 and 3655 cm2 at the booting stage, respectively, and both were significantly (*p* ≤ 0.05) reduced at the flowering stage. The plant had four tillers in case of stress while the control had 5; the leaf area at this stage was 1898 cm2, while it was 1590 cm2 in salt stress conditions. The photosynthetic rate corresponded to the SPAD value, which showed a significant (*p* ≤ 0.05) decrease at the flowering stage (Figure 4). It was ~57 in the case of the control at the flowering stage, while it was reduced to ~46 once salt stress was applied. SPAD value is the measure of chlorophyll value. Both leaf area and photosynthetic rate were decreased significantly (*p* ≤ 0.05) by stress, resulting in significant reductions in total dry matter accumulation rates and final yields. The same trend of fresh and dry biomass was observed in our study, in which the application of stress considerably (*p* ≤ 0.05) reduced the biomass content of the wheat plant (Figures 5 and 6). This trend of photosynthetic rate was also correlated with the stomatal conductance (Figure 7b), transpiration rate (Figure 7a), and water use efficiency (Figure 7c). In April 2021, stressed wheat plants showed 8.9, 12, 9.8, and 8.9% lower stomatal conductance, transpiration rate, intercellular CO2, and water use efficiency, respectively than control plants.
