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Article

The Effects of Phased Warming during Late Winter and Early Spring on Grain Yield and Quality of Winter Wheat (Triticum aestivum L.)

by
Haiwang Yu
1,
Zhen Gao
1,
Jingshan Zhao
2,
Zheng Wang
2,
Xiaoyu Li
1,
Xinyan Xu
1,
Huajian Jian
1,
Dahong Bian
1,
Yanhong Cui
1 and
Xiong Du
1,*
1
State Key Laboratory of North China Crop Improvement and Regulation/Key Laboratory of North China Water-Saving Agriculture, Ministry of Agriculture and Rural Affairs/Key Laboratory of Crop Growth Regulation of Hebei Province/College of Agronomy, Hebei Agricultural University, Baoding 071001, China
2
Agricultural Project Monitoring Center of Hebei Province, Shijiazhuang 050052, China
*
Author to whom correspondence should be addressed.
Agronomy 2023, 13(7), 1909; https://doi.org/10.3390/agronomy13071909
Submission received: 21 June 2023 / Revised: 16 July 2023 / Accepted: 17 July 2023 / Published: 19 July 2023
(This article belongs to the Section Farming Sustainability)
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Abstract

:
Phased warming in late winter and early spring can increase winter wheat grain yield. However, the effects of different durations of warming during this period on winter wheat grain yield and quality are not yet clear. Therefore, this study conducted field warming experiments in a movable polyethylene greenhouse during the late winter and early spring stages of the three wheat growing seasons from 2019 to 2022. The results showed that the accumulated growing degree days (GDD) of the warming treatment during the warming period were increased by 87.3–215.7 °C d compared to the control (CK). The warming treatment advanced and prolonged the duration of vegetative growth and spike differentiation after regreening, promoted spike and flower development, and increased grain length, grain width, and grain area. During the three growing seasons, the longer the warming duration (WD) of the warming treatment, the more obvious were the observed promoting effects on the kernel number per spike and 1000-kernel weight. From 2019 to 2021, compared to the CK, the spike number per unit area and grain yield of the warming treatments increased with the prolongation of WD. However, in the 2022 growing season the spike number per unit area and grain yield of the warming treatment were increased with longer WD, reaching the maximum at WD of 56 days and then gradually decreasing with longer WD. Compared to CK, the grain protein content, wet gluten content, and sedimentation value of the warming treatment decreased with the prolongation of WD. The promotion effect of longer WD on grain starch content and protein yield was more significant. In summary, the accumulated GDD during the warming period compared to CK was 155.8–181.2 °C d, and at WD of 50–56 days a relatively higher grain yield and protein yield could be obtained.

1. Introduction

The IPCC report indicates that the global warming trend remains unchanged. Compared to the period of 1850–1900, the global mean surface temperature increased by 1.1 °C in the past decade (2011–2022), and is predicted to continue to rising by 1.4 °C to 4.4 °C within this century [1]. Global warming exhibits asymmetric features, with higher temperature increases in winter and spring than in summer and autumn [2]. The temperature in China has shown an upward trend [3]. The North China Plain was the most significant region in China where climate warming was apparent, with a higher tendency of warming in winter and spring than in summer and autumn [4]. This led to a rapid and brief warming in the spring and frequent high-temperature and dry winds after wheat anthesis, which shortened the grain filling time and hindered the formation of grain yield components and grain quality [5,6]. Wheat (Triticum aestivum L.) is one of the world’s essential food crops, and the North China Plain, as the main wheat-producing area in China, accounts for 6.2% and 10.6% of the world’s wheat harvest area and production, respectively [7]. Wheat yield has a vital role in China’s food security as well as globally.
Climate warming will alter the growth and development process of wheat [8,9,10]. Studies have indicated that, for every 1 °C increases in the minimum temperature on the North China Plain, wheat regreening advances by 10.5 days [11]. Tao et al. [12] suggested that during the period from 1981 to 2018 climate warming resulted in a reduction in the duration of winter wheat growth by 4.2 days per decade. The spike differentiation stage is a critical period for the formation of wheat reproductive organs as well as a key period in determining wheat yield. The influence of spikelet differentiation on wheat yield formation is mainly achieved through the kernel number per spike [13]. Li et al. [14] conducted a study and found that winter warming advanced the single-ridge stage by 5–28 days, the double-ridge stage by 3–24 days, and the floret differentiation stage by 1–18 days. Therefore, winter warming advanced and prolonged the spike differentiation stage of wheat during the overwintering period [15]. However, the effects of periodic warming during late winter and early spring on spikelet development and morphological changes remain unclear.
High temperatures lead to reduced wheat yields [16,17]. Previous research has shown that for each 1 °C increase in mean annual temperature above 15 °C, yields decrease by 3–4% [18]. However, under sufficient moisture conditions climate warming could benefit wheat yield [19]. One study has found that with an increase of 1.5 °C in the daily mean temperature during the entire growth period of wheat there was a significant increase in both the kernel number per spike and the 1000-grain weight, as well as an increase in the filling rate of inferior grains, resulting in a significant increase in grain yield [8]. The frequency and duration of global high temperatures has gradually increased, and the response of plants to temperature is influenced by the duration and intensity of exposure [20]. Although the promoting effect of late winter and early spring warming on wheat yield has been proven [21], limited research had been carried out on the effects of the duration of late winter and early spring warming on wheat. Therefore, investigating the impact of different durations of late winter and early spring warming on winter wheat yields can provide important evidence for evaluating potential changes in wheat yield under climate warming.
Protein content and starch content are important indicators determining wheat quality. Previous studies have found that post-anthesis warming significantly reduces winter wheat grain weight, grain length, grain width, and grain starch content while significantly increasing grain protein content, sedimentation value, and wet gluten content [22]. A longer duration of post-anthesis warming resulted in higher grain protein content and lower starch content [23]. However, the longer the duration of high-temperature conditions after anthesis, the greater the decrease in grain weight [24]. Research has shown that compared to nighttime warming during winter and spring, continuous nighttime warming during winter and spring has a greater promoting effect on grain weight and grain protein formation in winter wheat [25]. However, while increasing grain weight during the entire growth period, warming reduced grain protein content and increased grain starch content [26]. This indicates that the effects of different warming periods and durations on grain quality vary. Therefore, it is of great significance to clarify the effects of different durations of warming during late winter and early spring on grain quality.
Previous studies have evaluated the effects of climate warming on the growth and development of wheat through winter–spring warming, post-anthesis warming, or whole growing season warming [8,27,28]. However, there are few reports on the effects of different durations of winter–spring warming on winter wheat grain yield and quality. Therefore, this study used a movable polyethylene greenhouse to conduct field warming experiments, aiming to explore the relationship between different durations of winter-spring warming and grain yield and quality. Our study can provide support for exploring the potential yield and quality improvement of winter wheat in the North China Plain against the background of climate warming.

2. Materials and Methods

2.1. Site Description

The field experiments were conducted at the Shenzhou (Shenzhou, China) Experimental Station of Dry Farming and Water-Saving Agriculture, Hebei Academy of Agricultural and Forestry Sciences (115.71° E, 37.91° N, altitude 20 m) in the wheat growing seasons from 2019 to 2022. During the 2019–2022 growing seasons, the rainfall and daily average temperature from sowing to maturity were 204.6 mm and 8.6 °C, 125.0 mm and 8.2 °C, and 160.6 mm and 7.3 °C, respectively (Figure 1). The topsoil (0–20 cm) was a typical loamy soil with an organic matter content of 12.53 g kg−1, total nitrogen content of 65.8 g kg−1, available potassium content of 121.9 g kg−1, and available phosphorus content of 15.3 mg kg−1. The ecological and production conditions of the experimental station represented those of the northern part of the North China Plain.

2.2. Experimental Design and Field Management

The winter wheat variety “Hengguan 35” (semi-winter) was used in the field experiment. The sowing dates for the 2019–2020 and 2020–2021 growing seasons were both 12 October, with a sowing rate of 187.5 kg ha−1. In the 2021–2022 season, excessive rainfall (precipitation during the period of 1 October 2021 to 20 October 2021) amounted to 83.0 mm before sowing, which delayed the sowing date to 22 October 2021, with a sowing rate of 280 kg ha−1. The plot area was 16 m2 (4 m × 4 m, row spacing of 15 cm). Prior to sowing wheat, all the previous crop maize straw was crushed and returned to the field and base fertilizer was applied with N 135 kg ha−1, P 135 kg ha−1, and K 180 kg ha−1. Quantitative irrigation of 75 mm was applied at the stem elongation, anthesis, and grain filling stages to ensure no drought stress during the wheat growing season. Nitrogen fertilizer (N) of 135 kg ha−1 was applied with irrigation during stem elongation. Weeds, pests, drought, and diseases were well controlled by seed coating, herbicides, irrigation, etc.
A randomized block experimental design with three replicates for each treatment was used in this study. Four warming treatments were set during the 2019–2021 (2020 and 2021) growing season, with natural condition as the control (CK); the start dates of the other three warming treatments were 25 January (WT1), 1 February (WT2), and 8 February (WT3), and the end date of warming was 20 March for all treatments. Based on the experimental results of the wheat growing seasons from 2019 to 2021, we believe that the most suitable start date for warming in the late winter and early spring stage was 25 January. To verify the effects of different warming end dates on wheat under the condition of the most suitable warming start date, five warming treatments were set in the 2021–2022 (2022) growing season, with natural conditions as the control (CK); the start date of warming was 25 January for all treatments, and the end dates of warming were 5 April (WTI), 28 March (WTII), 20 March (WTIII), and 12 March (WTIV), respectively.
The present study conducted field warming experiments using a simple polyethylene-covered steel frame greenhouse which had dimensions of 4 m in length, 4 m in width, and 0.85 m in height. To control the air temperature and relative humidity inside the greenhouse, ventilation was conducted from 9:00 a.m. to 4:00 p.m. every day (with the ventilation opening located on the shaded side), and the other three sides were sealed by compacted soil to prevent excessive temperature rise inside the greenhouse.

2.3. Sampling and Measurements

2.3.1. Growth Period and Spike Differentiation Period of Wheat

When 50% of the spring leaves of all plants in the field reached 1–2 cm in length, this was recorded as the regreening stage (regreening). When the first node was detectable, this was recorded as the stem elongation (Z31) stage. When the flag leaf sheath was extending, this was recorded as the booting (Z41) stage. When anthesis was beginning, it was recorded as the anthesis (Z61) stage. Finally, when the caryopsis was hard (difficult to divide with the thumbnail), this was recorded as the maturity (Z91) stage. [29]. Each treatment was observed using a stereomicroscope (OLYMPUS-SZX10, OLYMPUS, Tokyo Metropolis, Japan) and a digital camera (OLYMPUS-EP50, OLYMPUS, Tokyo Metropolis, Japan) for spikelet development every three days starting from 25 January 2022. The developmental characteristics of the spikelets were observed according to the criteria of Waddington et al. [30] (Table A1). The total number of florets (TNF) and the number of fertile florets (NFF) were recorded.

2.3.2. Temperature Monitoring

Each treatment used an automatic temperature datalogger (Model MicroLite5008, Fourtec, Rosh HaAyin, Israel) placed inside a louver box to automatically record the canopy air temperature every 10 min. Growing degree days (GDD) were calculated by accumulating the daily mean temperature above 0 °C during the growing season [27]. Daily mean temperature (DMT) was the mean of all daily temperature data in 10 min intervals. Meteorological data were obtained from an automatic weather station at the experimental station.

2.3.3. Grain Filling and Yield Determination

During the anthesis, 30 wheat spikes that bloomed simultaneously in each plot were marked and three spikes were sampled every five days from the seventh day after anthesis, with three replicates. The grains were stripped and dried to measure their dry weight and calculate the grain filling rate. After wheat maturation, an area of 1 m × 0.9 m in the center of each plot was selected and harvested, the grains were threshed after drying to 14% moisture content, and the yield per unit area was calculated. Before harvesting, a double row of 1 m was selected at the center of each plot, the number of effective spikes was counted, and the spike number per unit area was calculated based on the row spacing. Additionally, 50 spikes were randomly harvested from each plot to examine the total number of spikes (TNS), number of fertile spikelets (NFS), kernel number per spike, and 1000-kernel weight.

2.3.4. Determination of Grain Quality

After natural air-drying of grains harvested during three growing seasons, grain protein content, wet gluten content, and sedimentation value were determined using a near-infrared grain quality analyzer (Perten-DA7250, Perten Instruments AB, Segeltorp, Sweden). Grain length, grain width, and grain area were measured using a high-speed HD doc scanner (S500A3B, Eloam, China). Dried grain samples were ground and sieved through a 40-mesh sieve to obtain the test sample. The starch content of the grain was determined using an anthrone colorimetric method [31]. Specifically, 50 mg of dried powder was placed in a centrifuge tube with 10 mL of 3 mol/L HCl and heated in a 100 °C water bath for 45 min. After cooling to room temperature, the liquid and residue were transferred to a 50 mL volumetric flask and 8 mL of 3 mol/L NaOH was added before filling with distilled water. A diluted test solution of 200 μL was taken and mixed with 800 μL of 0.2% anthrone (prepared with 98% H2SO4) and shaken. The mixture was heated in a 100 °C water bath for 5 min, cooled, and the absorbance was measured at 620 nm using a microplate reader (Epoch 2 Microplate Spectrophotometer, Bio Tek Corporation, Winooski, VT, USA).

2.3.5. Data Analysis

The data were collected and statistically analyzed using Microsoft Excel 2021 and SPSS 25.0 (SPSS Inc., Chicago, IL, USA). Graphs were created using SigmaPlot 14.0, Adobe Illustrator CC 2021 (Adobe, San José, CA, USA), and ChiPlot (https://www.chiplot.online, accessed on 21 March 2023).

3. Results

3.1. Growing Degree Days (GDD) and Daily Mean Temperature (DMT)

In the 2020 and 2021 growing seasons, the warming duration (WD) and warming increase magnitude (WM) of the warming treatment were 22–56 days and 2.6–4.2 °C, respectively. In the 2021 growing season, the WM showed a decreasing trend with the extension of the WD. Meanwhile, for every 14 days of advance in the warming start date, the GDD between 21–38.5 °C during the warming period was higher in the warming treatment than that in the control (CK) (Table 1). In the 2022 growing season, the WD and WM of the warming treatment were 48–71 days and 3.7–4.7 °C, respectively, and the WM showed a decreasing trend with the extension of the WD. During the warming period of the 2020 and 2021 growing seasons, the DMT of the warming treatment decreased with the advance of the warming start date, while in the 2022 growing season the DMT of the warming treatment increased with the advance of the warming end date.
In the three growth seasons the warming treatment advanced the regreening date by 0–23 days compared with CK, and the subsequent growth stages were advanced as well (Table A2). In the 2020 and 2021 growing seasons, with every 14 day advance in the warming start date from the regreening to maturity, GDD increased by 10.3–34.8 °C d. However, there was no change in GDD among the warming treatments in the 2022 growing season. During the three growing seasons, the DMTs of the warming treatments were lower than that of CK in the stages of booting to anthesis and anthesis to maturity (Table 2).

3.2. Growth Duration (GD)

During the 2020 growing season, the growing duration (GD) of WT3 under warming treatment was the same as that of CK, while in 2021 it was shortened by 3 days compared to CK (Table 2). In contrast, during the 2020 and 2021 growing seasons WT1 and WT2 showed an extended GD of 4–17 days from regreening to maturity compared to CK. In the 2022 growing season, the GD under warming treatment from regreening to maturity was extended by 18–19 days compared to CK. This indicates that there are differences in the effects of different warming start and end dates on wheat growth and GD.
During the 2020 and 2021 growing seasons, compared to CK, the warming treatment extended the GD from stem elongation to booting and from anthesis to maturity by 9–12 days and 1–7 days, respectively, and showed a trend of longer GD with earlier warming start date and longer WD. Interestingly, in the 2022 growing season, the warming treatment again showed an extension in the GD from stem elongation to booting and from anthesis to maturity compared to CK while showing a trend of longer GD with earlier warming end date and shorter WD from stem elongation to booting (Table 2).

3.3. Spike Differentiation

In the 2022 growing season the warming treatment advanced the single-ridge stage (W2) by 18 days compared with CK, the floret primordium differentiation stage (W3.5) advanced by 16 days, and the stigma feather formation stage (W9.5) advanced by 8–12 days. At the same time, warming treatment had lower DMT than CK at each spike differentiation stage owing to advancing growth stage. Correspondingly, warming treatment extended the grain filling duration (GD) by 2 days from W2 to W3.5 and by 4–8 days from W3.5 to W9.5 (Table 3). The spike differentiation process is shown in Figure 2. Meanwhile, the length of young spikes at different spike differentiation stages under warming treatment was higher than that of CK, and showed a trend of increasing with the prolongation of WD (Figure 3).

3.4. Spike Length, Total Number of Spikelets (TNS), Number of Fertile Spikelets (NFS), Total Number of Florets (TNF), and Number of Fertile Florets (NFF)

In the three growing seasons the warming treatment significantly increased the spike length of wheat compared to the CK (Figure 4) as well as significantly increasing the total number of spikelets (TNS), number of fertile spikelets (NFS), total number of florets (TNF), and number of fertile florets (NFF) (Figure 5). Meanwhile, the promotional effect of warming treatment on spike length, TNS, NFS, TNF, and NFF of winter wheat was greater with a larger increase in GDD and longer WD during the warming period compared to CK.

3.5. Grain Weight and Filling Rate during Grain Filling Process

In all three growing seasons, the time when different treatments reached their maximum grain filling rate was effectively the same. The final grain weight and average grain filling rate during the grain filling process were higher in the warming treatment than in CK. Compared with CK, the final grain weight and average grain filling rate with the different warming treatments showed an increasing trend with the prolongation of WD in different growing seasons (Figure 6).

3.6. Yield and Yield Components

In the 2020 and 2021 growing seasons, compared with CK, the grain yield with warming treatment increased by 3.1–24.6% and 4.9–28.3%, respectively. At the same time, the promotional effect of phased warming in late winter and early spring on grain yield, spike number per unit area, kernel number per spike, and 1000-grain weight of winter wheat were increased with the extension of WD (Table 4). During the growing season of 2022, the grains yield and spike number in the warming treatments showed an increasing trend compared to the CK with the extension of the WD, reaching the maximum increase at a WD of 56 days (WTIII), and gradually decreased with the extension of the WD; the minimum increase was observed at a WD of 71 days (WTI) (Table 4 and Figure 7A). During the 2022 growing season, the promotional effect of the warming treatment on the kernel number per spike and 1000-kernel weight increased with the extension of WD.
The kernel number per spike was negatively correlated with the daily mean temperature (DMT) from stem elongation to anthesis stage during all three growing seasons. During the stem elongation to anthesis stage in the 2022 growing season, the DMT with the warming treatments increased with earlier termination dates of warming. However, the kernel number per spike continued to exhibit an increasing trend with the extension of WD (Figure 7B). From 2019 to 2022, the 1000-kernel weight decreased with increasing DMT from anthesis to the maturity stage, reaching a significant level in the 2020 growing season. For every 1 °C increase in DMT from anthesis to maturity stage the 1000-kernel weight decreased by 2.3 g, 1.4 g, and 2.7 g, respectively (Figure 7C). In the 2020 and 2021 growing seasons, the greater the GDD accumulated during the warming period compared to the control (CK), the greater the increase in grain yield. In the 2022 growing season, the maximum grain yield was observed at a GDD increase of 181.2 °C d during the warming period, which then declined with further increases in GDD (Figure 7D).

3.7. Grain Quality

In the 2019–2022 seasons, warming treatments resulted in a decrease of 0.4–5.9%, 0.3–4.6%, and 0.2–5.8% in grain protein content, wet gluten content, and sedimentation value, respectively, as compared to CK, and showed a trend of greater reduction with prolonged of WD (Figure 8 and Figure 9). In the 2020 and 2021 growing seasons, warming treatments increased grain protein yield and starch content by 2.7–22.4% and 1.7–10.2% compared to CK, respectively. In the 2022 growing season warming treatments increased the grain protein yield and starch content by 1.3–18.1% and 1.3–6.3%, respectively, compared to CK, with starch content increasing with the extension of WD. The grain protein yield showed a trend of increasing first and then decreasing with the extension of WD. Meanwhile, phased warming in late winter and early spring increased the grain length, grain width, and grain area in all three growing seasons (Figure 10).

3.8. Relationship between Grain Quality and Temperature

Correlation analysis showed that the accumulated difference in growing degree days (GDD) between the warming treatment and CK during the warming period was significantly negatively correlated with grain protein content (PC), wet gluten content (WGC), and sedimentation value (SV) and was significantly positively correlated with the grain starch content (SC), grain length (GL), grain width (GW), and grain area (GA), while it was positively correlated with grain protein yield, though there was no significant difference. On the contrary, the DMT during anthesis to the maturity stage exhibited a significant positive correlation with PC, WGC, and SV, while it displayed a significant negative correlation with SC, GL, GW, and GA (Figure 11).

4. Discussion

4.1. Phased Warming in Late Winter and Early Spring Increased Grain Number per Spike by Prolonging the Spikelet Differentiation Period

Climate warming has a significant promotional effect on the growth and development of wheat [11]. In this study, late winter and early spring temperature increases raised the canopy temperature of winter wheat during the warming period by 2.6–4.7 °C compared to the CK at ambient temperature (Table 1), while shortening the overwintering period, advancing regreening, and extending the subsequent active growth periods (Table A2), thereby favoring the accumulation of assimilates in wheat plants. Previous studies have indicated that wheat spike differentiation occurs during the stem elongation stage [32]; thus, the extension of this stage (i.e., from terminal spikelet initiation to anthesis) is beneficial for spikelet development (Table 2). In the 2022 growing season, we found that the kernel number per spike with the warming treatments was positively correlated with the duration of the period from stem elongation to anthesis (DMT), contrary to the trends observed in the 2020 and 2021 growing seasons. This may be due to the relatively low temperature environment caused by the termination of warming, which slows spike development. Specifically, as the termination date of warming is delayed, the DMT (from stem elongation to anthesis) increases and the impact of the relatively low temperature environment on spike development rate decreases, favoring spikelet development in winter wheat and ultimately increasing the kernel number per spike.
Rapid spring warming in the North China Plain has been shown to shorten the spike differentiation period, which is unfavorable for the kernel number per spike [33]. However, previous studies have suggested that early spring warming extends the spike differentiation period by exposing the post-regreening growth stage of wheat to a relatively low-temperature environment. This prolongation promotes spikelet development by increasing the photosynthetic area and providing sufficient assimilates for young spikes [21]. Our experiment demonstrates that late winter and early spring warming can advance the spike differentiation period and lower the environmental temperature during spike differentiation (Table 3), resulting in significantly increased length of both young and final spikes (Figure 3 and Figure 4) while markedly enhancing the NFS and NFF (Figure 5), thereby significantly increasing the kernel number per spike (Table 4). These results are consistent with previous research findings [9,27,34].

4.2. Excessively Prolonged Duration of Artificial Warming in Late Winter and Early Spring Is Unfavorable for Increasing Grain Yield

The grain filling stage is a critical period for wheat yield formation, with both the rate and duration of grain filling being highly susceptible to environmental temperature [35]. Previous studies have shown that high temperatures after anthesis shorten the duration of grain filling and increase the abortion rate of inferior grains, reducing the kernel number per number and grain weight [36]. However, phased warming during late winter and early spring has been found to advance the growth and development of wheat by placing the wheat in a relatively lower environmental temperature during the grain filling stage [21]. In this experiment, the warming treatment reduced the daily mean temperature during the anthesis to maturity stage by 0.9 °C–2.1 °C compared to the CK, extended the duration of grain filling, and increased the grain filling rate (Figure 6), providing sufficient time and resources for grain weight accumulation [37]. Concurrently, a negative correlation was observed between the DMT during the anthesis-to-maturity stage and grain traits (Figure 11), indicating that lower post-anthesis temperatures favor increased grain length, grain width, and grain area (Figure 10). There was a significant correlation between grain traits and grain weight [38]. In summary, phased warming during late winter and early spring extended the duration of grain filling and increased the grain filling rate by lowering the environmental temperature during the post-anthesis stage of wheat, thereby improving grain characteristics, increasing grain storage capacity, and ultimately promoting grain weight increase. Previous studies have suggested that early spring warming significantly increases the flag leaf area after anthesis in wheat and delays flag leaf senescence [21], ensuring an ample supply of assimilates for grain filling and significantly increasing grain weight (Table 4).
An appropriate warming duration during late winter and early spring can increase the effective tiller number of winter wheat, while an excessively long duration of warming leads to premature differentiation and death of weak tillers, resulting in a significant decrease in the number of spikes [39]. In this study, the spike number of wheat increased with the extension of the WD in the 2020 and 2021 growing seasons. However, in the 2022 growing season the spike number exhibited a similar increasing trend within an appropriate warming duration (WD ≤ 56 days) while showing a declining trend with further extension of the WD (Figure 7A). This indicates that an excessively long duration of warming during the late winter and early spring stage reduces the effective tiller number of wheat, leading to a decrease in spike number and adversely affecting yield formation.
Our study demonstrates that lower environmental temperatures during the stem elongation to anthesis stage promote the formation of kernel number per spike (Figure 7B), resulting in a significant increase in kernel number per spike, which is consistent with previous research findings [34]. Winter warming can significantly increase wheat yield [40]; however, an excessively long duration of winter warming during the overwintering period has been found to be detrimental to grain yield formation [39]. In the 2020 and 2021 growing seasons, the warming treatment showed a positive correlation between the accumulated growing degree days (GDD) during the warming period and grain yield compared to the control (CK). However, in the 2022 growing season grain yield exhibited a trend of first increasing and then decreasing with the increase in GDD (Figure 7D), indicating that excessive GDD (prolonged warming duration) was unfavorable for grain yield improvement. By analyzing the grain yield trends across the three growing seasons, in this study the increase in GDD during the warming period compared to CK ranged from 155.8–181.2 °C d, and a warming duration of 50–56 d resulted in relatively higher grain yield (Figure 8D). Thus, it is evident that an appropriate duration of warming during the late winter and early spring stage is crucial for enhancing grain yield in winter wheat.

4.3. Effects of Phased Warming in Late Winter and Early Spring on Grain Quality of Winter Wheat

Extensive research has been conducted by previous scholars on the impact of warming on wheat grain quality [41,42,43]. High temperatures during the grain filling stage can significantly increase sedimentation value and wet gluten content while reducing amylose starch content [44]. Warming throughout the entire growth period can significantly increase the nitrogen, protein, and carbon content of winter wheat grains while decreasing the carbon-to-nitrogen ratio [45]. However, studies have additionally suggested that warming throughout the entire growth period can enhance the activities of sucrose synthase (SS), ADP-glucose pyro phosphorylase (AGPase), and starch branching enzyme (SBE) during grain filling, promoting the conversion of sucrose to starch, thereby increasing starch content and grain weight while reducing protein content [46,47]. Wet gluten content and sedimentation value are important indicators reflecting wheat protein quantity and quality, and serve as crucial criteria for evaluating grain quality [48]. In our study, the warming treatment resulted in a decrease in grain protein content, wet gluten content, and sedimentation value while increasing grain starch content (Figure 9 and Figure 10). This may be attributed to the greater promoting effect of the warming treatment on starch-synthesizing enzymes, leading to an increase in the carbon-to-nitrogen ratio of the grains and consequently reducing the relative protein content. Elevated post-anthesis temperatures in wheat can inhibit sucrose synthesis and suppress SS activity, impeded the conversion of sucrose to starch [49]. However, winter and spring nighttime warming could enhance SS activity in grains [25]. Our correlation analysis indicates a significant positive correlation between DMT from anthesis to maturity and grain protein content and a significant negative correlation with starch content (Figure 11). This could be attributed to the relatively lower environment temperature after anthesis, which enhanced SS activity in grains, thereby promoting starch accumulation. Similar to findings in previous studies [50], although the warming during late winter and early spring led to a decrease in grain protein content, the significant increase in grain yield contributed to an increase in grain protein yield (Figure 8). However, further in-depth investigations are required to elucidate the physiological effects of late winter and early spring warming on grain quality formation. This study makes conjectures about the future trends in grain yield and quality of winter wheat in the North China Plain under an asymmetrical warming scenario while offering empirical data to substantiate these speculations.

5. Conclusions

Phased warming during late winter and early spring caused wheat to regreen earlier and extended the duration of subsequent growth stages, benefiting spikelet development and floret differentiation. This promoted accumulation of assimilates in winter wheat plants, significantly increased spikelet length, and significantly improved the number of fertile spikes and florets, providing the time and material foundation for kernel number formation. The warming treatment significantly enhanced grain length, grain width, and grain area, resulting in expanded grain capacity. Phased warming during late winter and early spring significantly increased the kernel number per spike and 1000-kernel weight in winter wheat. However, a prolonged warming duration led to earlier differentiation of tiller polarities, resulting in a changing pattern of an initially increasing and then decreasing spike number per unit area and grain yield. Warming caused a decrease in grain protein content, wet gluten content, and sedimentation value, while increasing the starch content and protein yield.

Author Contributions

Conceptualization, H.Y. and Z.G.; Data curation, H.Y. and X.L.; Resources, H.Y.; Investigation, H.Y., X.L. and X.X.; Software, H.Y.; Visualization, H.Y.; Writing—original draft, H.Y. and Z.G.; Formal analysis, Z.G., Z.W., H.J. and D.B.; Writing—review and editing, Z.G., J.Z. and X.D.; Supervision, Y.C. and X.D.; Funding acquisition, X.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Key Research and Development Program of Hebei Province (grant number: 20326414D and 21327001D), State Key Laboratory of North China Crop Improvement and Regulation (grant number: NCCIR2021ZZ-09 and NCCIR2022ZZ-12), Natural Science Research Project of Higher Education in Hebei Province (grant number: BJK2022009), and Startup Fund of Hebei Agricultural University (grant number: YJ201827).

Data Availability Statement

The data included in this research are available upon request by contact with the corresponding author.

Acknowledgments

This work was supported by the Key Research and Development Program of Hebei Province (grant number: 20326414D and 21327001D), State Key Laboratory of North China Crop Improvement and Regulation (grant number: NCCIR2021ZZ-09 and NCCIR2022ZZ-12), Natural Science Research Project of Higher Education in Hebei Province (grant number: BJK2022009), and Startup Fund of Hebei Agricultural University (grant number: YJ201827). Financial support from the above sources is gratefully acknowledged.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Table
Table A1. Spike developmental score of wheat.
Table A1. Spike developmental score of wheat.
Spike Developmental Stage and Its CharacteristicDevelopmental Phase
Single ridge stageW2
Double ridge stageW2.5
Glume primordium presentW3
Lemma primordium presentW3.25
Floret primordium differentiation stageW3.5
Pistil primordium presentW4.25
Carpel primordium presentW4.5
Carpel extending round three sides of ovuleW5
Stylar canal closing; ovarian cavity enclosed on all sides but still open aboveW5.5
Stylar canal remaining as a narrow opening, two short round style primordia presentW6
Style begin elongationW6.5
Stigmatic branches just differentiating as swollen cell on stylesW7
Single-celled villi differentiate on ovary wall: stigma branches elongateW7.5
Stigmatic branches and hairs on ovary wall elongationW8
Stigmatic branches and hairs on ovary wall continue to elongate, stigmatic branches from a tangled massW8.5
Styles and stigmatic branches erect, stigmatic hairs differentiatingW9
Styles and stigmatic branches spreading outwards, stigmatic hairs well developed (stigma feather formation stage)W9.5
Styles curved outwards and stigmatic branches spread wide, pollen grains and well-developed stigmatic hairsW10
Table
Table A2. Dates of different growth stages in this experiment.
Table A2. Dates of different growth stages in this experiment.
Y 1T 2Growth Period (Day/Month)
RegreeningZ31 3Z41 4Z61 5Z91 6
2020WT131 January8 March6 April22 April4 June
WT212 February9 March7 April25 April5 June
WT319 February12 March8 April28 April6 June
CK21 February24 March11 April3 May8 June
2021WT129 January9 March8 April23 April3 June
WT211 February10 March9 April25 April4 June
WT320 February12 March9 April29 April6 June
CK20 February25 March12 April3 May9 June
2022WTI30 January12 March7 April24 April4 June
WTII30 January12 March9 April24 April4 June
WTIII30 January12 March10 April25 April5 June
WTIV30 January12 March12 April25 April5 June
CK22 February28 March18 April2 May9 June
1 Y: year; 2 T: treatment; 3 Z31, 4 Z41, 5 Z61 and 6 Z91 indicated stem elongation, booting, anthesis and maturity, respectively.

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Agronomy 13 01909 g001 550
Figure 1. Daily maximum temperature, average temperature, minimum temperature, and precipitation during the winter wheat growing seasons of 2019–2020 (2020), 2020–2021 (2021), and 2021–2022 (2022).
Figure 1. Daily maximum temperature, average temperature, minimum temperature, and precipitation during the winter wheat growing seasons of 2019–2020 (2020), 2020–2021 (2021), and 2021–2022 (2022).
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Figure 2. Effect of phased warming in late winter and early spring on spike differentiation process in 2022 growing season.
Figure 2. Effect of phased warming in late winter and early spring on spike differentiation process in 2022 growing season.
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Figure 3. Effects of phased warming in late winter and early spring on young spike length (2021–2022). W2, W3.5, and W5 refer to glume primordium present, floret primordium present, and carpel extending around three sides of the ovule, respectively. Means were compared by Tukey’s test, and the different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
Figure 3. Effects of phased warming in late winter and early spring on young spike length (2021–2022). W2, W3.5, and W5 refer to glume primordium present, floret primordium present, and carpel extending around three sides of the ovule, respectively. Means were compared by Tukey’s test, and the different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
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Agronomy 13 01909 g004 550
Figure 4. Effects of phased warming in late winter and early spring on spike length (maturity). Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
Figure 4. Effects of phased warming in late winter and early spring on spike length (maturity). Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
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Agronomy 13 01909 g005 550
Figure 5. Effects of phased warming in late winter and early spring on spike traits of winter wheat. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
Figure 5. Effects of phased warming in late winter and early spring on spike traits of winter wheat. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
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Agronomy 13 01909 g006 550
Figure 6. Effects of phased warming in late winter and early spring on grain dry matter accumulation and grain filling rate. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05; ns means non-significant. Error bars indicate the standard error (n = 3).
Figure 6. Effects of phased warming in late winter and early spring on grain dry matter accumulation and grain filling rate. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05; ns means non-significant. Error bars indicate the standard error (n = 3).
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Agronomy 13 01909 g007 550
Figure 7. (A) Relationship between warming duration and spike number; (B) relationship between daily mean temperature (Z31–Z61) and kernel number per spike; (C) relationship between daily mean temperature (Z61–Z91) and 1000-kernel weight; (D) relationship between growing degree days and grain yield. GDD: growing degree days (the difference between the growing degree days of warming treatments and CK during the warming period).
Figure 7. (A) Relationship between warming duration and spike number; (B) relationship between daily mean temperature (Z31–Z61) and kernel number per spike; (C) relationship between daily mean temperature (Z61–Z91) and 1000-kernel weight; (D) relationship between growing degree days and grain yield. GDD: growing degree days (the difference between the growing degree days of warming treatments and CK during the warming period).
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Agronomy 13 01909 g008 550
Figure 8. Effects of phased warming in late winter and early spring on grain protein content, protein yield, and starch content. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
Figure 8. Effects of phased warming in late winter and early spring on grain protein content, protein yield, and starch content. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
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Agronomy 13 01909 g009 550
Figure 9. Effects of phased warming in late winter and early spring on wet gluten content and sedimentation value of grains. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
Figure 9. Effects of phased warming in late winter and early spring on wet gluten content and sedimentation value of grains. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
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Agronomy 13 01909 g010 550
Figure 10. Effects of phased warming in late winter and early spring on grain traits. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
Figure 10. Effects of phased warming in late winter and early spring on grain traits. Means were compared by Tukey’s test. The different letters above each bar indicate a significant difference at p < 0.05. Error bars indicate the standard error (n = 3).
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Figure 11. Correlation analysis of temperature change, grain quality, and grain traits (2019–2022). GDD: growing degree days (the difference between the growing degree days of warming treatments and CK during warming period), DMT: daily mean temperature, PC: protein content, PY: protein yield, SC: starch content, WGC: wet gluten content, SV: sedimentation value, GL: grain length, GW: grain weight, GA: grain area. The number above each box is the correlation coefficient; *, **, and *** indicate significant differences at the p < 0.05, <0.01, and <0.001 probability levels, respectively. The colors reflect the changes in the correlation coefficient: red represents the correlation coefficients with high and positive correlation, while green indicates high and negative correlation.
Figure 11. Correlation analysis of temperature change, grain quality, and grain traits (2019–2022). GDD: growing degree days (the difference between the growing degree days of warming treatments and CK during warming period), DMT: daily mean temperature, PC: protein content, PY: protein yield, SC: starch content, WGC: wet gluten content, SV: sedimentation value, GL: grain length, GW: grain weight, GA: grain area. The number above each box is the correlation coefficient; *, **, and *** indicate significant differences at the p < 0.05, <0.01, and <0.001 probability levels, respectively. The colors reflect the changes in the correlation coefficient: red represents the correlation coefficients with high and positive correlation, while green indicates high and negative correlation.
Agronomy 13 01909 g011
Table
Table 1. The changes in daily mean temperature and warming magnitude between warming treatments during the treatment period.
Table 1. The changes in daily mean temperature and warming magnitude between warming treatments during the treatment period.
Y 1T 2Treatment Date (Day/Month)GDD 3
(°C d)		WD 4 (d)WT-
DMT 5 (°C)		CK-
DMT 6 (°C)		WM 7
(°C)
2020WT125 January–20 March155.8567.14.32.7
WT28 February–20 March125.8428.55.53.0
WT322 February–20 March87.3338.45.72.6
2021WT125 January–15 March156.1509.05.83.2
WT28 February–15 March135.13610.97.13.8
WT322 February–15 March93.02211.87.64.2
2022WTI25 January–5 April214.3718.64.93.7
WTII25 January–28 March215.7648.03.94.1
WTIII25 January–20 March181.2567.23.14.1
WTIV25 January–12 March176.5487.12.44.7
1 Y: year; 2 T: treatment; 3 GDD: growing degree days (The growth degree day of warming treatment increased compared with CK during warming period); 4 WD: warming duration; 5 WT-DMT: The daily mean temperature of warming treatment during warming period; 6 CK-DMT: The daily mean temperature (field ambient temperature) of CK during warming; 7 WM: warming increase magnitude (The increased daily mean temperature of warming treatment compared with CK during warming period).
Table
Table 2. Growth duration (GD), growing degree days (GDD), and daily mean temperature (DMT) of warming treatments and CK.
Table 2. Growth duration (GD), growing degree days (GDD), and daily mean temperature (DMT) of warming treatments and CK.
Y 1T 2Regreening-Z31 3Z31-Z41 4Z41-Z61 5Z61-Z91 6
GDGDDDMTGDGDDDMTGDGDDDMTGDGDDDMT
(d)(°C d)(°C)(d)(°C d)(°C)(d)(°C d)(°C)(d)(°C d)(°C)
2020WT137210.95.729344.011.916215.113.444945.421.5
WT226174.86.729348.712.018236.713.142933.522.2
WT322173.47.927326.512.120271.513.640912.022.8
CK32232.47.318194.910.822366.516.737851.723.0
2021WT139329.28.430443.514.815235.215.742868.820.7
WT227281.110.430442.914.816251.215.741866.721.1
WT321223.011.028411.814.720319.616.039854.721.9
CK33306.79.318288.216.021333.415.938867.522.8
2022WTI41298.47.326300.511.617290.317.142908.821.6
WTII41299.77.328332.611.915256.117.142908.821.6
WTIII41281.46.929338.011.715258.217.242915.121.8
WTIV41307.97.531356.611.513213.816.442915.121.8
CK34272.18.021304.114.514249.817.839899.823.1
1 Y: year; 2 T: treatment; 3 Z31, 4 Z41, 5 Z61 and 6 Z91 indicated stem elongation, booting, anthesis and maturity, respectively.
Table
Table 3. The spike differentiation date, growth duration (GD), growing degree days (GDD), and daily mean temperature (DMT) of WT and CK in the 2022 growing season.
Table 3. The spike differentiation date, growth duration (GD), growing degree days (GDD), and daily mean temperature (DMT) of WT and CK in the 2022 growing season.
T 1W2 2–W3.5 3W3.5–W9.5 4
DateGDDGDDMTDateGDDGDDMT
(Day/Month)(°C d)(d)(°C)(Day/Month)(°C d)(d)(°C)
WTI8 February–12 March264.2328.312 March–20 April534.74013.4
WTII8 February–12 March264.9328.312 March–24 April612.84414.0
WTIII8 February–12 March255.1328.012 March–24 April596.24413.6
WTIV8 February–12 March279.8328.712 March–24 April570.34413.0
CK26 February–28 March264.0308.828 March–2 May572.33615.9
1 T: treatment; 2 W2, 3 W3.5, and 4 W9.5 corresponded to the single ridge stage, floret primordium differentiation stage, and stigma feather formation stage.
Table
Table 4. Effects of phased warming in late winter and early spring on grain yield and yield components of winter wheat.
Table 4. Effects of phased warming in late winter and early spring on grain yield and yield components of winter wheat.
Y 1T 2Spike Number
(×104 ha−1)		Kernel Number
per Spike		1000-Kernel
Weight (g)		Grain Yield
(kg ha−1)
2020WT1395.56 a46.20 a48.82 a6932.03 a
WT2387.78 ab44.33 ab47.19 ab6406.1 ab
WT3373.33 ab42.15 b46.22 b5735.00 bc
CK365.56 b38.59 c45.16 b5562.50 c
2021WT1384.44 a45.60 a48.41 a6830.17 a
WT2374.44 a43.40 ab46.15 a6255.85 a
WT3362.22 a40.75 b45.83 a5582.46 b
CK357.78 a37.95 c44.99 a5323.16 b
2022WTI483.33 b47.48 a50.71 a10,254.71 bc
WTII542.22 a46.67 a49.74 a10,634.64 abc
WTIII573.33 a44.98 a48.86 ab11,718.47 a
WTIV554.44 a44.88 a47.56 ab10,890.33 ab
CK527.78 ab38.40 b45.78 b9532.04 c
1 Y: year; 2 T: treatment. Means were compared by Tukey’s test, and Means were compared by Duncan’s test, and different letters after the values indicate a significant difference at p < 0.05.
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Yu, H.; Gao, Z.; Zhao, J.; Wang, Z.; Li, X.; Xu, X.; Jian, H.; Bian, D.; Cui, Y.; Du, X. The Effects of Phased Warming during Late Winter and Early Spring on Grain Yield and Quality of Winter Wheat (Triticum aestivum L.). Agronomy 2023, 13, 1909. https://doi.org/10.3390/agronomy13071909

AMA Style

Yu H, Gao Z, Zhao J, Wang Z, Li X, Xu X, Jian H, Bian D, Cui Y, Du X. The Effects of Phased Warming during Late Winter and Early Spring on Grain Yield and Quality of Winter Wheat (Triticum aestivum L.). Agronomy. 2023; 13(7):1909. https://doi.org/10.3390/agronomy13071909

Chicago/Turabian Style

Yu, Haiwang, Zhen Gao, Jingshan Zhao, Zheng Wang, Xiaoyu Li, Xinyan Xu, Huajian Jian, Dahong Bian, Yanhong Cui, and Xiong Du. 2023. "The Effects of Phased Warming during Late Winter and Early Spring on Grain Yield and Quality of Winter Wheat (Triticum aestivum L.)" Agronomy 13, no. 7: 1909. https://doi.org/10.3390/agronomy13071909

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