*2.1. Experimental Site and Environmental Conditions:*

Pot experiments were carried out during the wheat growing season in 2020–2021 (2021) at the Agricultural Experiment Station (32◦39 N, 119◦42 E) of Agricultural College, Yangzhou University, in China. Winter wheat (Yangmai 25) was grown in the pot field. Each experiment consisted of five developmental phases (overwintering, jointing, booting, flowering, and maturity), with 6 seeds of Yangmai 25 genotype grown in individual pots (Figure S2). Four stresses were chosen: waterlogging, salt stress, heat, and the combined effect of these three stresses, which were monitored at different growth stages (Figure S3). Due to the abundant rainfall in this area, we did not need to irrigate during the wheat growing season. However, if necessary, the pots were irrigated with tap water accordingly to retain the field capacity required for healthy wheat growth.

The experiment was a completely randomized design with SCU treatment (control— SCU only) as the main plot and stress as the subplot. There were four stress treatments (waterlogging, salt stress, heat, and combined). There were five plots in the experiment (Figure S2). Each treatment was conducted in triplicate and was subjected to the same field management. The N rate adopted in the experiment was 130 kg ha<sup>−</sup>1, consistent with the optimum N rate in all the treatments, including control (CK). Phosphate (114 kg ha−<sup>1</sup> P2O5) and potassium (62 kg ha−<sup>1</sup> K2O) fertilizers were applied once before sowing conferring to the pre-soil analysis report. Basal fertilizer was applied at a depth of 10–15 cm [22]. A total of six seeds of Yangmai 25 were sown in a 10 kg pot filled with a standard potting mixture [25] (Table S2).

The slow-release sulfur-coated urea (SCU; release time 120 days) was used as a stressalleviation substance at a recommended dose of 130 kg ha−<sup>1</sup> in all treatments, including the control. Seeds were sown on 8 November 2020, while sampling was performed at the overwintering stage (28 December 2020), jointing stage (12 March 2021), booting stage (30 Mar 2021), flowering stage (17 April 2021), and maturity stage (28 May 2021). The setups for the different abiotic stress applications were established as follows.

For the heat stress, plants were upraised with control plants until the flowering stage and then moved to the heat stress chamber (cryogenic room) for the remainder of the growth period (up to maturity). The plants were kept under a 16 h photoperiod duration and provided a light intensity of 350 μmol m−<sup>2</sup> s−<sup>1</sup> generated by metal halide lamps. The temperature treatment was as follows: the night temperature was kept at 20 ◦C, whereas the day temperature was gradually increased to 33 ◦C and held for 8 h, then subsequently decreased to 20 ◦C. The relative humidity (%RH) was kept at 64–68% and 76% during the day and night, respectively, in the stress chamber (Figures S1 and S3).

For waterlogging stress, plants were grown with control plants, and stress was applied from germination to the overwintering stage (35 days). Waterlogging was applied using water from a nearby water service by flooding the pots allocated for the waterlogging treatments. The soil was moisturized using water above field capacity using incessant flooding, generally every day, to produce an oxygen-deficient atmosphere. For this purpose, pots were placed in a water basin (i.e., used for nursery rice growing). There was a storage tank on one side and a drainage valve on the other side. The standing water level was maintained at ~12 cm. Water was replaced after 4–7 days according to weather and water conditions. For replacing water, a drainage valve was opened according to the storage tank valve so that the water level could be maintained. The soil moisture content was measured by an oven-drying method using 1 g of soil sample at 105 ◦C overnight [26]. In control, the soil moisture content was <85%, while it was from 85 to 100% for the stressed plants (Figures S1 and S3).

For salt stress, a 15 mM sodium chloride (NaCl) solution was used as a source, while plants were grown with control plants under the same conditions. The salt stress was applied after the jointing stage and continued until maturation (Figures S1 and S3).

For combined stress, plants were grown in waterlogged stress, and after the jointing stage, salt stress was applied. After the flowering stage, these plants were transferred to the heating chamber, and they continued to grow there until the maturation stage (Figure S3). In total, the experimental setup consisted of 1 genotype × 3 pots × 4 abiotic stresses × 5 developmental stages × 1 fertilizer (SCU: for all treatments including control) × 6 seeds per pot.

A control treatment was also established in triplicate in a separate plot containing the same SCU fertilizer but at a recommended dose of 130 kg ha−<sup>1</sup> (Figure S2). A separate pot experiment without any stress and fertilizer was also conducted under the same conditions to compare the nitrogen accumulation. Seeds were sown on 8 November 2020, and the wheat crop was harvested on 28 May 2021. During this study period, samples were collected at 5 stages: (1) overwintering stage: 28 December 2020; (2) jointing stage: 12 March 2021; (3) booting stage: 30 March 2021; (4) flowering stage: 17 April 2021; and (5) maturity stage: 28 May 2021.

#### *2.2. Procedure/Protocols for Growth and Yield Parameters*

Each experimental unit was measured for yield and yield-related characteristics, such as plant height, seeds per spike, total dry matter (kg ha−1), number of tillers per plant, grain yield (kg ha−1), average seeds weight per spike, and harvest index. Portable chlorophyll meters (SPAD-502, Konica Minolta, Osaka, Japan) and mobile photosynthesis systems (LI-6400, LI-COR Biosciences, Lincoln, NE 68504, USA) were used to collect data on physiological parameters, including chlorophyll content percent and net photosynthetic rate [26,27]. Wheat plants were harvested at various stages of development to measure fresh and dry biomass. An electrical weight balance was used to measure the fresh weight of leaves and stems. Then, oven drying of leaves and stems was done for 48 h (up to constant weight) at 70 ◦C, and the dry weight was calculated [24]. A leaf area meter (Model, CI-202, CID Bio-Science, Inc., 1554 NE 3rd Avenue, Camas, WA 98607, USA) was used to calculate the leaf area. At maturity, plants from three pots were collected from each experimental component, and various yield components were quantified. The final yield and biomass of the entire experimental unit were assessed separately, and on the rationale of dry biomass production, transformed into kg ha−1. The activity of photosynthetic properties, fluorescence, photosynthetic rate, stomatal conductance, the intercellular CO2 concentration of the plants, transpiration rate, and water use efficiency were all measured

with a portable system (LI-6400, Li-Cor Inc., USA). Water use efficiency was also calculated (photosynthetic rate divided by transpiration rate) following the methodology of a previous study [24]. All analyses were performed in triplicate, and mean values were calculated.
