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Article

Effects of Deficit Irrigation on Spring Wheat Lignification Process, Yield Productivity and Stalk Strength

by
Yaoyuan Zhang
1,
Haojie Yin
2,
Rongrong Wang
1,
Fangfang He
1 and
Guiying Jiang
1,*
1
College of Agronomy, Shihezi University, Shihezi 832003, China
2
Agricultural and Rural Bureau, Deyang 618500, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(11), 2647; https://doi.org/10.3390/agronomy14112647
Submission received: 28 September 2024 / Revised: 5 November 2024 / Accepted: 7 November 2024 / Published: 10 November 2024
(This article belongs to the Section Water Use and Irrigation)
Browse Figures
Versions Notes

Abstract

:
Moderate deficit irrigation can improve lignin metabolism, thereby increasing wheat yield and lodging resistance. The moisture-sensitive variety Xinchun 22 (XC22) and drought-resistant variety Xinchun 6 (XC6) were used as experimental materials. We set mild drought (T1, J1 and 60–65% FC, where FC is the field capacity) and moderate drought (T2, J2 and 45–50% FC) during the tillering stage (T) and the jointing stage (J). We used conventional drip irrigation as a control (CK and 75–80% FC). The results show that the activity of lignin synthesis-related enzymes decreased with the growth process, while the accumulation and monomer content of lignin increased under different water treatments. The lignin metabolism and morphological characteristics of XC6 were higher than those of XC22. Under the same processing conditions, the indicators of XC22 showed more significant changes and were more sensitive to changes in the moisture content. Compared with other treatments, the stem thickness and wall thickness of the J1 treatment increased by 0.86–23.49% and 1.72–23.58%. The yield of the T1 treatment was the highest, increasing by 3.05–44.06% compared to other treatments. In addition, by improving PAL, H-type lignin monomers, S-type lignin monomers, stem thickness and lignin metabolism, grain yield can be increased. After mild drought during the jointing stage, J1 significantly improved the lignin metabolism capacity of the stem, increased stem thickness and wall thickness, and was beneficial for improving lodging resistance. The T1 treatment favored the improvement of the production capacity of assimilates, thus promoting a high yield of spring wheat.

1. Introduction

The Xinjiang region is known for its diverse agriculture, growing a wide range of crop species, including cotton, wheat and maize [1,2]. In recent years, wheat production has reached a record high [3]. However, lodging is one of the main factors limiting wheat yield and quality and increasing harvest costs [4,5]. According to a survey, lodging will reduce the yield of drip-irrigation wheat by 20–30%. In severe cases, the yield will be reduced by more than 40% [6,7]. In addition, agricultural activities consume a large amount of water. Limited water resources have become an important constraint to agricultural development in arid and semi-arid zones [8]. Several modern irrigation methods have been proposed to address this issue, such as mobile drip irrigation and center pivot irrigation [9,10]. Current drip-irrigation technology to achieve the integration of water, fertilizers and pesticides with high irrigation efficiency has become the main technology for the green production of wheat in Xinjiang [11,12]. The high irrigation quantity mode of close planting and “a small number of times” is adopted in the wheat production of drip irrigation in Xinjiang. However, the excessive amount of irrigation under the condition of close planting makes the internodes at the base of the wheat stalk longer. The height of its center of gravity is higher, the stalk wall is thinner, and the mechanical strength declines, increasing lodging danger, which is not conducive to a high and stable yield of wheat [13,14,15]. Therefore, under integrated water and fertilizer management, it is important to explore water regulation during the growth period to improve stalk quality. Specifically, enhancing the mechanical strength of the basal internodes can increase crop lodging resistance. This approach has significant practical implications for realizing the water-saving and high-yield potential of drip-irrigated wheat in arid regions.
The lodging resistance of wheat is closely related to the mechanical strength of the stalk. Lignin is one of the main secondary metabolites that determines the cell wall strength and the mechanical strength of the stalk. The stiffness and mechanical strength of the stalk are given by cross-linking with lignin monomers [16,17], and it is this fundamental factor that determines the lodging resistance of crop stalks [18,19]. Lignin is polymerized from lilac-based lignin (S), guaiacyl lignin (G) and p-hydroxyphenyl lignin (H) [20], among which the S-type lignin plays the main mechanical supporting role [21]. A high content of G and S monomers and a low proportion of H monomers are typical characteristics of lodging resistance in wheat [22,23]. However, Muhammad et al. [24] thought that the lower the proportion of S monomers and the higher the ratio of H monomers and G monomers, the more beneficial to improve the folding resistance of wheat. PAL, 4CL, TAL and CAD are important regulatory enzymes in the pathway of lignin biosynthesis [25]. The higher the expression of the lignin synthase gene, the stronger the enzyme activity and increased lignin synthesis [26,27]. The lignin content and activities of the PAL, TAL, CAD and 4CL of lodging-resistant wheat varieties were higher than those of lodging-sensitive wheat varieties [28]. Irrigation reduced the lignin content. Reducing the amount of irrigation increased the lignin content by 13.0–27.5% [29], while the wheat stalk lignin content decreased under flooded conditions, and the PAL activity also significantly decreased [30]. Ma et al. [31] found that through moderate regulated deficit irrigation in the early growth stage, wheat could shorten the length of the first and second internodes of the stalk, which was beneficial to the synthesis and distribution of lignin in the basal internodes, improve the mechanical strength of the stalk and enhance the lodging resistance. Therefore, appropriate water management measures can regulate the activities of key enzymes in lignin metabolism, promote lignin synthesis and reduce the risk of lodging.
Rational irrigation is the key to ensuring a high yield of wheat. At present, most studies have focused on the effects of the nitrogen application rate and ratio and the water–nitrogen interaction on stalk lignin metabolism and lodging resistance [5,32]. However, there is a lack of systematic research on the regulation of stalk lignin metabolism by drought–rewatering during crop growth. In particular, the relationship between lignin metabolism and stalk lodging resistance in drip-irrigation wheat is not clear. We assume that adaptive deficit irrigation can regulate wheat lignin metabolism to a certain extent and improve stem strength, as well as enhance the physiological function of the basal internodes of spring wheat stalks and ultimately improve the lodging resistance and yield of spring wheat. Therefore, we applied varying levels of drought stress at the tillering and jointing stages of wheat under drip irrigation. We analyzed the characteristics of the accumulation and distribution of lignin in the second internode of stalk bases. Meanwhile, we clarified the changes in lignin and its monomer content regulated by the activities of the key enzymes in lignin metabolism, and we elucidated the intrinsic mechanism of lignin metabolism that regulates stalk strength and yield formation. This paper provides a theoretical basis for exploring the water-saving potential, high-yield, stable-yield, and stress-resilient cultivation of drip-irrigated wheat in arid regions.

2. Materials and Methods

2.1. Overview of the Experimental Site

This experiment was conducted from April to July of 2022–2023 at the experimental station of the School of Agriculture, Shihezi University. The daily highest temperature occurred from June to July during the wheat growth period. The total solar radiation in the region was 1588.6 kWh·m−2 (2022) and 1579.9 kWh·m−2 (2023). The meteorological indicators are shown in Figure 1. The basic fertility characteristics of the soil at 0–40 cm before sowing are shown in Table 1.

2.2. Experimental Design

This experiment adopted a split-plot design. Spring wheat varieties were set as the main zone, and moisture treatments were set as the secondary zone. Xinchun22 (XC22, moisture-sensitive, medium tillering capacity, medium resistance to inversion and good stability of yield) and Xinchun6 (XC6, moisture-insensitive, tolerant to salinity, resistant to disease and high productivity) were test materials. Three degrees of water deficit (maximum field holding capacity, FC) were set for each fertility period: normal water (75–80% FC), mild deficit (60–65% FC) and moderate deficit (45–50% FC). To ensure that the rewatering time of the mild and moderate drought was the same, water control was carried out 10 d earlier for the moderate drought compared to the mild drought at the tillering stage. Water control was carried out 6 d earlier for the moderate drought compared to the mild drought at the jointing stage, and the drought treatment time was 7 d after the corresponding soil moisture content was reached. When the drought was over, the drip rate was increased to 75–80% FC (called rewatering). The specific design is shown in Table 2. All treatments were performed in triplicate.
The test plot area was 12 m2. The field plots were planted in a “one tube for four rows” planting system. The nitrogen fertilizer used in the experiment was urea (N = 46%), the phosphorus fertilizer was superphosphate (P2O5 = 12%), and the nitrogen fertilizer base to top dressing ratio was 3:7. A total of 120 kg·ha−1 P2O5 and 255 kg·ha−1 pure N was applied during the growth period. Before this, sowing, plowing, raking and sunning the ground were carried out. Then, we mixed all the phosphorus fertilizers and basal N fertilizers into the soil. The top dressing was applied at 20%, 40%, 35% and 5% along with water through drip-irrigation belts during the tillering, jointing, booting, flowering and filling stages. The plots were buried with a 60 cm deep and 20 cm wide impermeable membrane to prevent water infiltration. According to the pattern of the “one tube for four rows” planting system, we determined the spacing of wheat sowing and the position of the drip-irrigation tape. Then, we determined the position of the watermark (Figure 2). After the preliminary work of sowing was completed, we used a trencher to manually sow seeds and installed the drip-irrigation system (drip-irrigation tape, nutrient tube and fertilizer irrigation) (Figure 2). After the sowing work was completed, we observed the developmental stage of the wheat every day to determine the irrigation time and amount. We planted on 1 April 2022 and 3 April 2023. We harvested on 6 July 2022 and 7 July 2023.
Soil moisture changes were monitored using a watermark resistive moisture tension sensor (model 200 SS; Irrometer Co., River-side, CA, USA). The sensor was buried vertically in the soil (Figure 2). Soil was taken near the watermark. We divided the soil into two parts and measured the soil moisture content and maximum field water-holding capacity separately, thus calculating the proportion of soil moisture content to the maximum field water-holding capacity. We obtained a fitting curve between the watermark readings and the proportion of soil moisture to the maximum field capacity (Figure A1). Finally, the current soil water content was calculated from the curve, and the irrigation volume was calculated using Equation (1). The amount of irrigation water was calculated using the following equation [33]:
m = 10ρb H(βI − βj)
where m is the irrigation water volume (mm); ρb is the soil bulk weight (g·cm−3); H is the soil depth (cm), and the depth of water control is 40 cm; βI is the target water content (field water-holding capacity × target relative water content); and βj is the current soil water content.

2.3. Measurement Items and Methods

We picked ten single stalks from each replicate of each treatment at the flowering (days 60–65), milk ripening (days 72–78) and wax ripening stages (days 83–88) of the wheat. We removed the spikes and leaves and then cut different internodes and classified them. The second internode of the stalk base (I2) of 5 plants was used to measure stalk thickness and wall thickness. Then, the I2s were quickly frozen in liquid nitrogen and stored in a refrigerator at −80 °C for the determination of lignin accumulation and its key enzymes in the wheat stalks. The I2s of the other 5 samples were dried at 105 °C for 30 min, followed by 80 °C, to a constant weight for the determination of the lignin monomer content.

2.3.1. Phenylalanine Ammonia-Lyase (PAL) Activity

The onset and end absorbance values at 290 nm were determined using a UV spectrophotometer, with a 0.02 mol·L−1 phenylalanine solution as the substrate. Enzyme-specific activity was calculated based on a 0.01 change in the OD290 nm value per hour as the enzyme activity unit (U). Please refer to the method of Assis et al. [34] for specific details.

2.3.2. Tyrosine Ammonia-Lyase (TAL) Activity

The onset and end absorbance values at 315 nm were determined using a UV spectrophotometer, with a 0.02 mol·L−1 tyrosine solution as the substrate. Enzyme-specific activity was calculated based on a 0.01 change in the OD315 nm value per hour as the enzyme activity unit (U). Please refer to the method of Wajahatullah et al. [35] for specific details.

2.3.3. Cinnamyl Alcohol Dehydrogenase (CAD) Activity

The onset and end absorbance values at 340 nm were determined using a UV spectrophotometer, with a 1 mol·L−1 trans-cinnamic acid solution as the substrate. Enzyme-specific activity was calculated based on a 0.01 change in the OD340 nm value per hour as the enzyme activity unit (U). Please refer to the method of Morrison et al. [36] for specific details.

2.3.4. Peroxidase (POD) Activity

The onset and end absorbance values at 470 nm were determined using a UV spectrophotometer, with guaiacol as the substrate. Enzyme-specific activity was calculated based on a 0.01 change in the OD470 nm value per hour as the enzyme activity unit (U). Please refer to the method of Moerschbacher et al. [37] for specific details.

2.3.5. Lignin Content

Determination referred to the method of Cheng et al. [38]. Lignin accumulation was indicated as an absorbance value per unit mass of fresh samples at 280 nm (OD·g−1 FW).

2.3.6. Lignin Monomer Content

Determination referred to the method of Zheng et al. [39]. The samples were qualitatively and quantitatively determined using an ultra-high-performance liquid chromatography-triple quadrupole mass spectrometer (Xevo TQ-S, Waters, Milford, MA, USA).

2.3.7. Morphological Characteristics

We used a vernier caliper to measure the inner and outer diameters of the middle section of the joint. The outer diameter was the stalk thickness. Wall thickness = outer diameter-inner diameter.

2.3.8. Yield and Its Composition

Wheat plants of 1 m2 were selected in each plot at maturity and harvested by hand. The number of wheat ears per unit area was measured, 20 spikes were randomly selected from them, and the number of grains per spike was determined. All harvested wheat spikes were threshed, dried and weighed. A thousand-kernel weight was determined, and the yield was calculated. All treatments were performed in triplicate.

2.4. Data Analysis

The analysis of variance (ANOVA) and Duncan’s multiple range test were performed using SPSS 20. software. The Pearson correlation coefficient was used to analyze the degree of correlation between the indicators. Regression analyses were used to establish functional relationships between the different indicators. On the SSPSRO (www.spsspro.com) platform, a structural model was built using partial least squares regression to reflect the linkage between different latent variables. We used Origin software for drawing.

3. Results

3.1. Effects of Drought Stress on Lignin Metabolism of Basal Internodes of Spring Wheat Stalks Under Drip Irrigation

3.1.1. Key Enzymes of Lignin Metabolism

As shown in Figure 3A–D, PAL, TAL, CAD and POD enzyme activities decreased with the progress of the growth process. Drought stress had a significant effect on the four types of enzyme activities (p < 0.05). Drought treatment at the tillering stage and the jointing stage can significantly increase the four types of enzyme activities, which increased by 0.95–44.58% and 1.53–57.78% compared with the CK treatment, respectively, and they began to decrease gradually after rewatering. After all treatments were rehydrated, the changes in the four types of enzyme activities of the two varieties were the same, which showed that J1 > J2 > T2 > T1 > CK. J1 of XC6 increased by an average of 1.53–73.46%, and the J1 of XC22 increased by an average of 0.58–88.80% compared to the other treatments. The PAL, TAL, CAD and POD enzyme activities of XC6 increased by an average of 10.95–34.23%, 8.97–28.09%, 12.53–55.21% and 12.44–29.67% compared to those of XC22 under the J1 treatment.
Based on the above analysis, mild drought during the jointing stage (J1) and rehydration was more conducive to the increase and maintenance of PAL, TAL, CAD and POD enzyme activities in the later stages of growth and promoted lignin metabolism. In addition, the interaction between drought treatment and variety had a significant impact on PAL and TAL enzyme activity during the flowering, milk ripening and maturity stages (p < 0.01), CAD enzyme activity during the flowering and milk ripening stages, and POD enzyme activity during the flowering and maturity stages (Table 3).

3.1.2. Lignin Content

As shown in Figure 4, the lignin content increased with the growth process. Compared with the flowering stage, the lignin content of XC6 increased by 14.62–33.37% and 34.62–45.65%, respectively, in the milk stage and the mature stage. XC22 increased by 11.40–20.22% and 24.88–31.15%. The lignin content was significantly affected by drought stress. Drought treatment can significantly increase the lignin content. Compared with CK, the average increase in the lignin content at the tillering stage and the jointing stage was 2.21–12.00% and 9.19–25.13%, respectively. The lignin content of the two varieties behaved consistently, with J1 > J2 > T2 > T1 > CK. The lignin content of J1 of the two varieties increased by 3.68–23.13% and 6.79–25.45%, respectively, compared with other treatments, and XC6 was 0.75–11.89% higher than XC22. Mild drought during the jointing stage (J1) and rehydration were favorable to the post-flowering lignin content and increased wheat yield. The effect of drought treatment on the lignin content was highly significant (Table 3).

3.1.3. Lignin Monomers

As shown in Figure 5, G- and S-type monomers are the main types in the composition of wheat stalk lignin monomers, accounting for the proportions of G at 47.77–55.24% and S at 39.39–47.68% and are significantly higher than the H type (4.42–5.58%). With the advance of the growth process, the content of three kinds of lignin monomers, the proportion of the S-type monomer and the G + S monomers increased. The response of the three monomer contents to drought–rewatering at the different growth stages was the same as lignin. The H, G and S monomer contents of the drought treatments at the tillering stage and the jointing stage, respectively, increased by 0.63–29.45%, 0.21–16.72% and 0.13–20.52%, and 7.95–39.28%, 3.54%–44.64% and 5.45–41.18% compared with the CK treatment. After drought–rewatering, the changes in content among the three monomers were the same. Both for XC6 and XC22, the content variation among the three monomers was consistent, with J1 > J2 > T2 > T1 > CK, and the best performance was achieved under the J1 treatment. Under the J1 treatment of XC6, the average increase of H, G and S monomers was 3.19–39.28%, 2.52%–44.64% and 1.28–41.28% compared with the other treatments. Under the J1 treatment of XC22, the average increase of H, G and S monomers was 1.73–36.85%, 0.27–42.09% and 2.03–25.16% compared with the other treatments. Therefore, mild drought (J1) and rehydration at the jointing stage were more helpful for post-flowering lignin monomer content and promoted lignin synthesis, which, in turn, increased wheat yield and stalk mechanical strength. The effects of drought treatments and cultivars on the lignin monomer content were highly significant (Table 3).

3.2. Effects of Drought Stress on Stalk Diameter and Wall Thickness of Basal Internode of Spring Wheat Under Drip Irrigation

Stalk Diameter and Wall Thickness

Within the growth process, the stem thickness and wall thickness showed a decreasing trend and an initial increase followed by a decrease (Table 4). The two indexes were affected by drought stress, and the stalk diameter and wall thickness decreased with the increase of drought stress. Changes in the stalk thickness and wall thickness after rehydration in all treatments differed between the two varieties, but both of them showed the best performance under J1. XC6 showed that J1 > J2 > T1 > T2 > CK. Compared with CK, the stalk diameter and wall thickness of XC6 at T1, T2, J1 and J2 increased by 9.12–12.94%, 2.73–8.57%, 21.16–23.49%, 12.86–22.11% and 8.50–16.26%, 3.82–11.38%, 16.34–23.58%, 10.81–17.65%, respectively. The stalk diameter and wall thickness of the J1 treatment increased by 0.86–18.18% and 2.98–15.55% compared with the other treatments. XC22 showed J1 > T1 > J2 > T2 > CK. Compared with CK, the stalk diameter and wall thickness of XC22 at T1, T2, J1 and J2 increased by 6.43–17.79%, 2.25–7.96%, 12.62–19.57%, 3.86–9.34% and 11.79–22.11%, 2.34–15.15%, 15.87–24.24%, 3.97–15.91%, respectively. Compared with other treatments, the stalk diameter and wall thickness of the J1 treatment increased by 1.51–12.58% and 1.72–20.61%, respectively. Under J1 processing, XC6 was, on average, 8.66–11.21% and 2.01–9.49% higher than XC22, respectively. At the same time, the compensatory effect of mild drought during the jointing stage (J1) and rehydration was the greatest. Drought (J1)–rewatering in the middle growth stage promoted an increase in stalk diameter and wall thickness after anthesis and enhanced the grain yield of the wheat stalks. In addition, varieties and drought treatments had significant effects on the stalk diameter and wall thickness of the spring wheat stalks.

3.3. Effects of Drought Stress on Yield and Components of Spring Wheat Under Drip Irrigation

3.3.1. Changes in Yield and Its Components

The yield and its composition were affected by drought (Table 5). Among all the drought stress treatments, the yield and composition of mild drought at the tillering stage (T1) were the best (except for the spike number). The spike number was the best at the jointing stage (J1). However, for different varieties, the changes in the trend of the yield and composition were different. For XC6, the trends in yield, grain number per spike, and thousand-grain weight for each treatment were T1 > J1 > CK > T2 > J2, and the T1 treatment showed an average increase of 3.05–24.77%, 2.15–16.61% and 1.27–12.69% compared to the other treatments. The drought treatment during the tillering stage mainly reduced the number of spikes, with an average decrease of 0.61–3.70% compared to CK. The yield compensation effect generated by the T1 treatment was higher than that of other treatments. The yield, grain number per spike, and thousand-grain weight of XC22 decreased in the order of T1 > CK > J1 > T2 > J2, and T1 was, on average, 3.13–44.06%, 0.03–17.05% and 1.20–19.23% higher than the other drought treatments. From the perspective of yield composition, drought stress reduced the number of spikes in XC22, and it decreased in the order of CK > J1 > T1 > J2 > T2. Compared to the different growth stages, the recovery degree of mild drought–rewatering in the tillering stage was larger, and the yield of XC6 was higher than that of XC22 by 0.85–23.46% under the T1 treatment. Drought treatments and varieties had significant effects on yield (p < 0.05). Based on the results, the T1 treatment can increase the yield and compensate for yield loss caused by drought by increasing the number of grains per ear and 1000-grain weight.

3.3.2. Correlation Analysis of Yield and Its Components

A path analysis of the yield and its components under water stress at different stages was carried out. With the spike number (X1), grain number per spike (X2) and 1000-grain weight (X3) as independent variables and yield (Y) as a dependent variable, a fitting equation was established using stepwise regression. XC22 was Y = 356.85X2 − 6524.28 (R2 = 0.959 **), and the independent variables X1 and X3 were eliminated by stepwise regression. The result shows that the effects of XC22’s spike number and 1000-grain weight on yield were lower than that of the grain number per spike (X2, p = 0.979 **) under drought stress in different periods. TXC6 was Y = 249.10X3 − 4623.52 (R2 = 0.924 **), and the independent variables X1 and X2 were eliminated by stepwise regression. The result shows that the effects of XC6’s spike number and grain number per spike on yield were lower than that of the 1000-grain weight (X3, p = 0.961 **) under drought stress in different periods. Under the conditions of this experiment, the number of grains per ear of XC22 had a positive impact on yield, while the 1000-grain weight of XC6 had a greater positive effect on yield. Therefore, grain yield can be increased by increasing the number of grains per spike and 1000-grain weight.

3.4. Correlation and Path Analyses Between Stalk Lignin Metabolism, Stalk Diameter, Wall Thickness and Yield

Correlation analyses were made between the SC metabolic parameters; PAL, TAL, CAD and POD enzymes; H, G, and S lignin monomers; total lignin content (LIG); stalk diameter (X1); wall thickness (X2) and yield (Y) in the second internodes of stalks (Figure 6). There was a significant negative correlation between the yield (Y1) and H-type lignin monomer content, indicating that the goal of high yield can be achieved by reducing the H-type lignin monomer content.
Taking yield (Y1), spike number (Y2), grain number per ear (Y3) and 1000-grain weight (Y4) as dependent variables and PAL (X1), TAL (X2), CAD (X3), POD (X4), H-type lignin (X5), G-type lignin (X6), S-type lignin (X7), LIG (X8), stalk diameter (X9) and wall thickness (X10) as independent variables, path analysis was carried out to determine the indexes that had more significant effects on yield (Y1), spike number (Y2), grain number per spike (Y3) and 1000-grain weight (Y4) (Table 6). According to the absolute value, the direct effect of the independent variables on yield (Y1) was the H-type lignin monomer (X5, p = |−0.314|); the direct effects of the independent variables on the spike number (Y2) were stalk diameter (X9, p = 0.719) > PAL (X1, p = |−0.398|) > S-type lignin monomer (X7, p = |−0.318|); the direct effects of independent variables on the grain number per ear (Y3) were in the order of the H-type lignin monomer (X5, p = |−0.296|) > stalk diameter (X9, p = 0.251); and the direct effect of independent variables on 1000-grain weight (Y4) was the H lignin monomer (X5, p = |−0.312|). Therefore, improving the activities of the key enzymes of lignin metabolism, PAL, the content of H-type and S-type lignin monomers and stalk diameter played a positive role in increasing yield and its composition.

4. Discussion

4.1. Effects of Drought Stress on Lignin Metabolism of Spring Wheat Stalks Under Drip Irrigation

PAL, TAL, CAD and POD enzymes are all important enzymes involved in lignin biosynthesis. An increase in their activity will lead to an increase in the total amount of lignin, resulting in stronger stalk rigidity [40]. Drought stress induction can increase the activity of key enzymes in lignin biosynthesis and significantly increase the content of lignin [41]. This study reaches the same conclusion that the enzyme activities of the four key enzymes of lignin metabolism increased in varying degrees under drought stress. However, they decreased significantly after rehydration. The activities of the four enzymes all reached their peak at J1. It may be that the drought treatment at the jointing stage accelerated the lignification process of the stalks and made the enzyme activity decrease rapidly in the later stages. The activities of four enzymes in XC6 were higher than those in XC22 after rehydration. Lignin is an important component of structural carbohydrates in wheat stalks, which can enhance the mechanical strength of wheat stalks [42]. Studies have shown that varieties with strong lodging resistance have a higher lignin content in their stalk tissue. Higher lignin accumulation is more helpful in enhancing plant stalk lodging resistance [43], and reducing irrigation during the growth period can increase the lignin content [29]. This study shows that the lignin content of wheat stalks after anthesis increased with the growth process, and each drought treatment increased the lignin content. Drought at the jointing stage significantly increased the lignin content of the stalks. However, the accumulation rate of lignin became slower after rewatering, which may be due to the decomposition of the storage material in wheat stalks at the late growth stage and the damage of the material transport, which led to the slowdown of lignin synthesis. After all the treatments were rehydrated, the stalk lignin content of XC6 and XC22 was the highest under the J1 treatment, and the lignin content of XC6 increased by 0.75–11.89% compared with XC22 under the J1 treatment. In summary, mild drought at the jointing stage (J1) and rewatering are more beneficial to the increase in the stalk lignin content after the flowering stage and, subsequently, enhance stalk strength.
Stalk lignin is mainly divided into G-type, S-type and H-type, and G-type and S-type monomers [44]. It was found that the content and total amount of three kinds of lignin monomers in lodging-resistant varieties were higher than those in lodging-sensitive varieties [45]. The proportion and structure of lignin monomers can affect the folding resistance of wheat stalks. The lignin content of XC6 increased by 0.75–11.89% compared with XC22 under the J1 treatment. This study shows that the content and total amount of these three kinds of lignin monomers gradually increased with the progress of the growth process, the proportion of H-type monomers decreased, and the proportion of G+S increased. The content of these three kinds of lignin monomers was higher than those in the CK treatment under different drought stress. After rehydration in all the treatments, the changes in the contents of these three kinds of lignin monomers were the same. XC6 and XC22 had the highest content of the three kinds of lignin under the J1 treatment. This study shows that rewatering at the jointing stage with mild drought (J1) was more beneficial to the accumulation of lignin monomers in wheat stalks after anthesis. In addition, the activities of key enzymes in the lignin metabolism, lignin content and lignin monomer content of the water-insensitive variety XC6 were higher than those of the water-sensitive variety XC22 after drought and rewatering. It is possible that water-sensitive wheat varieties have a weaker physiological regulation of lignin synthesis pathways under drought stress, which affects the activity of the key enzymes involved in lignin metabolism. Ultimately, it leads to the inhibition of lignin synthesis. Therefore, mild drought during the jointing stage (J1) and rehydration are more conducive to the metabolism of lignin and the accumulation of monomers in wheat stems after flowering. However, further in-depth research is needed on the interaction mechanisms between various physiological indicators of different drought-resistant wheat varieties in response to drought stress at different growth stages, as well as the molecular regulatory mechanisms related to different physiological characteristics.

4.2. Effects of Drought Stress on Stalk Diameter, Wall Thickness and Yield of Spring Wheat Under Drip Irrigation

The stalk diameter and wall thickness of wheat stalks are important morphological characteristics of stalk lodging resistance. Increasing wheat stalk thickness can effectively improve the lodging resistance of wheat plants [46,47,48]. It was found that compared to traditional flood irrigation, the water-saving irrigation model was effective in increasing rice stem thickness, stem wall thickness, and internode fullness, which, in turn, resulted in higher bending resistance and lowering the rate of collapse [49]. Within the growth process, the stem thickness and wall thickness showed a decreasing trend and an initial increase followed by a decrease. In the later stage of different drought treatments, the stalk diameter and wall thickness of the basal internodes of the wheat stalks decreased continuously. This may be caused by the gradual decomposition of the storage matter in the wheat stalks and the continuous transportation to the grains, resulting in the decrease of matter accumulation in the wheat stalks. The reason for the increase in wall thickness under the J1 treatment may be that light water stress recovered faster than moderate water stress at the jointing stage, and the photosynthetic assimilates, which wheat plants can transport to the internodes, increased, which increased the accumulation of stalk assimilates and promoted an increase in the wall thickness. After the J1 treatment, the stalk diameter and wall thickness of XC 6 and XC 22 were the largest, and the stalk diameter and wall thickness of XC6 were higher than those of XC22 by 8.66–11.21% and 2.01–9.49%. This indicates that drought-resistant varieties have a strong ability to adapt to adversity, and even after rehydration under drought stress, they can still maintain strong stem strength at all stages, thus resisting the effects of drought stress on wheat. The correlation analysis shows that there was a significant positive correlation between morphological characteristics and G and S lignin monomers and the key enzyme activity in lignin metabolism. In summary, drought treatment at the jointing stage promoted an increase in stalk diameter and wall thickness, which was more beneficial to improve the process of lignin metabolism in the later growth stage, and it improved the lodging resistance and yield of stalks. However, the effect of deficit irrigation intensity and duration on morphological characteristics needs to be studied in more detail to improve the system of regulating the effect of deficit irrigation on morphological characteristics.
Under drought stress, the grain yield, biomass and tiller number per plant were significantly affected [50,51,52]. Moderate deficit irrigation can promote the retransportation of dry matter stored in pre-anthesis vegetative organs to the grains after anthesis and optimize the yield structure, thus promoting the formation of the final yield. This can make up for the yield loss caused by a drought environment to a certain extent [53,54]. In addition, the optimization of deficit irrigation for maize was investigated, and it was found that reduced irrigation at specific stages can increase grain yield by up to 20% compared to constant deficit irrigation throughout the growth cycle [55,56]. However, even if the dry matter is transported to the grain in the nutrient organ, severe water stress cannot make up for the loss of grain yield [57,58]. In this study, different degrees of drought treatments at the tillering stage and the jointing stage had significant or extremely significant effects on the yield and its components, and the yield, grain number per spike and 1000-grain weight were the highest under mild drought treatment at the tillering stage (T1). The yield compensation effect of the T1 treatment was higher than that of other treatments, and the improvement in the drought-tolerant wheat variety XC6 was more significant. The spike number of the two wheat varieties reached its maximum under CK, followed by J1. Although the T1 treatment reduced the number of spikes, it increased the number of grains per spike and 1000-grain weight. It made up for the yield loss caused by the decrease in spike number and, finally, increased the yield of wheat. The jointing stage is the key period of stalk elongation and matter accumulation. Stress treatment at the jointing stage reduced the accumulation of storage matter before anthesis, especially for the water-sensitive varieties at the jointing stage [58]. In this study, we found that after moderate drought treatment at the tillering stage and the jointing stage, the yield decreased and did not increase after rewatering, and the yield loss of the water-sensitive variety XC22 was much higher than that of the drought-tolerant variety XC6. Further correlation and path analyses show that the activities of CAD and POD, the H-type lignin monomer content and stalk diameter had different effects on the yield and its composition. Therefore, the goal of increasing yield and resisting lodging can be achieved by improving lignin metabolism and morphological characteristics. Different degrees of drought stress can regulate lignin metabolism and morphological characteristics, thus affecting the stalk quality and grain yield (Figure 7). To sum up, regulated deficit irrigation–rewatering in the appropriate growth period is helpful to give full play to the physiological water-saving potential of wheat, and it achieves high-utility water under the premise of high and stable yield in arid areas. However, under deficit-regulated irrigation treatments, further investigations and analyses are still needed on how to exploit the characteristics of wheat at various fertility stages and thus balance high yield and high lodging resistance.
The water and nitrogen management system for crops may vary depending on soil conditions and crop stage growth characteristics. Increasing irrigation and fertilization during critical periods of crop fertilization can enhance water- and nitrogen-use efficiency [59]. Applying sufficient water during periods when plants are sensitive to water scarcity and applying water deficit during periods when plants are more resistant to water scarcity can alleviate concerns about yield decline. The impact of water deficit on crop yield depends on the specific phenological stage of the crop [60,61,62]. In addition, research has found that water and nitrogen inputs can be appropriately reduced while ensuring a maximum yield of 95% [63]. Combining the nitrogen application rate during the jointing stage with the irrigation lower limit of 65% and 70% of the irrigation rate during the jointing and late jointing stages can improve water- and nitrogen-use efficiency and increase wheat yield in North China [64]. In summary, researching deficit irrigation to maximize target benefits has become one of the hot topics today.

5. Conclusions

Appropriate deficit irrigation can regulate wheat lignin metabolism, thereby increasing yield and lodging resistance. In the farmland environment of the experimental area, the key enzyme activity, lignin content, three types of lignin monomer content, stem diameter and wall thickness of XC6 and XC22 were highest after rehydration under mild drought (J1 and 60–65% FC) during the jointing stage. All indicators of XC22 are lower than XC6. In addition, under different deficit irrigation treatments, XC22 showed more significant changes than XC6 and was more susceptible to changes in the moisture content. Therefore, mild drought treatment during the jointing stage (J1) is more conducive to promoting lignin metabolism in wheat straw. The J1 treatment also promoted an increase in wheat stem diameter and wall thickness, which is beneficial for improving the lodging resistance of wheat stems. Under mild water stress during the tillering stage (T1 and 60–65% FC), these two wheat varieties can ensure the number of grains per spike per unit area and increase grain weight. Therefore, it can achieve high yield. In addition, under T1 treatment, the water-sensitive variety XC22 can recover and maintain at the CK level to achieve stable yield. However, the water-insensitive variety XC6 can achieve high yields after rehydration, which are higher than the CK. In addition, farmers can adjust the irrigation volume and frequency of deficit-regulated irrigation appropriately according to the growth characteristics of different crops at different growth stages and soil moisture conditions.

Author Contributions

Conceptualization, Y.Z., G.J. and H.Y.; methodology, H.Y. and G.J.; software, Y.Z.; validation, Y.Z., H.Y. and R.W.; formal analysis, Y.Z., G.J. and H.Y.; investigation, F.H.; resources, R.W.; data curation, Y.Z.; writing—original draft preparation, Y.Z. and H.Y.; writing—review and editing, Y.Z. and G.J.; visualization, Y.Z.; supervision, R.W.; project administration, F.H.; funding acquisition, H.Y. and G.J. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the National Natural Science Foundation of China (32060422).

Data Availability Statement

The datasets generated for this study are available upon request to the corresponding authors.

Acknowledgments

The authors would like to thank the reviewers for their valuable comments and suggestions for this work. And the authors expressed their most sincere gratitude to the teachers and classmates at Shihezi University for their technical support during the experiment.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

4CL4-coumarate CoA ligase
CADCinnamyl alcohol dehydrogenase
GGuaiacyl lignin
Hp-hydroxyphenyl lignin
I2The second internode of stalk base
LIGLignin
PALPhenylalanine ammonia-lyase
PODPeroxidase
SLilac-based lignin
SCStructural carbohydrate
TALTyrosine ammonia-lyase

Appendix A

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Figure A1. Proportion of soil moisture content to maximum field capacity and watermark reading curve.
Figure A1. Proportion of soil moisture content to maximum field capacity and watermark reading curve.
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Figure 1. The temperature and precipitation for the spring wheat in 2022 and 2023.
Figure 1. The temperature and precipitation for the spring wheat in 2022 and 2023.
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Figure 2. Schematic diagram of drip tape and watermark layout.
Figure 2. Schematic diagram of drip tape and watermark layout.
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Figure 3. Effects of drought stress at different growth stages on the activities of PAL (A), TAL (B), CAD (C) and POD (D) enzymes in the second internodes of spring wheat stalk bases under drip irrigation. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period. Different lowercase letters indicate that different treatments of the variety have remarkable differences at 0.05 level.
Figure 3. Effects of drought stress at different growth stages on the activities of PAL (A), TAL (B), CAD (C) and POD (D) enzymes in the second internodes of spring wheat stalk bases under drip irrigation. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period. Different lowercase letters indicate that different treatments of the variety have remarkable differences at 0.05 level.
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Figure 4. Effects of drought stress at different growth stages on lignin content in the second internode of spring wheat under drip irrigation. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period. Different lowercase letters indicate that different treatments of the variety have remarkable differences at 0.05 level.
Figure 4. Effects of drought stress at different growth stages on lignin content in the second internode of spring wheat under drip irrigation. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period. Different lowercase letters indicate that different treatments of the variety have remarkable differences at 0.05 level.
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Figure 5. Effects of drought stress at different growth stages on lignin monomer content in the second internodes of spring wheat stalks under drip irrigation. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period.
Figure 5. Effects of drought stress at different growth stages on lignin monomer content in the second internodes of spring wheat stalks under drip irrigation. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period.
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Figure 6. Correlation between stalk SC metabolic parameters, stalk diameter, wall thickness and yield of spring wheat under drip irrigation and drought stress. Note: X1: stalk diameter; X2: wall thickness. * and ** demonstrate remarkable differences at the 0.05 and 0.01 standards.
Figure 6. Correlation between stalk SC metabolic parameters, stalk diameter, wall thickness and yield of spring wheat under drip irrigation and drought stress. Note: X1: stalk diameter; X2: wall thickness. * and ** demonstrate remarkable differences at the 0.05 and 0.01 standards.
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Figure 7. Adjusting deficit irrigation and drip irrigation to regulate lodging resistance and yield of spring wheat at different growth stages. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period. The red arrow (pointing upwards) represents the percentage increase in indicators under J1 treatment compared to other treatments.
Figure 7. Adjusting deficit irrigation and drip irrigation to regulate lodging resistance and yield of spring wheat at different growth stages. Note: FS: flowering stage, MS: milk ripening stage, MA: maturity period. The red arrow (pointing upwards) represents the percentage increase in indicators under J1 treatment compared to other treatments.
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Table 1. The major chemical characteristics of the experimental soil.
Table 1. The major chemical characteristics of the experimental soil.
YearTotal N (g·kg−1)Avail. N (mg·kg−1)Avail. P (mg·kg−1)Avail. K (mg·kg−1)Organic (g·kg−1)Soil Capacity
(g·cm−3)		Electrical Conductivity
(ds·m−1)		PH
20221.2653.3416.39147.0514.721.27 0.447.6
20231.3156.2716.25138.6316.211.280.447.8
Table 2. Drought stress test settings.
Table 2. Drought stress test settings.
TreatmentTillering StageJointing Stage
CK75–80% FC75–80% FC
T160–65% FC75–80% FC
T245–50% FC75–80% FC
J175–80% FC60–65% FC
J275–80% FC45–50% FC
Table 3. ANOVA of structural carbohydrate (SC) metabolic indicators of drip-irrigated spring wheat at different stages of drought stress.
Table 3. ANOVA of structural carbohydrate (SC) metabolic indicators of drip-irrigated spring wheat at different stages of drought stress.
TraitPALTALCADPOD
FSMSMAFSMSMAFSMSMAFSMSMA
C************************
T************************
C*T****************ns**ns**
TraitHGSLIG
FSMSMAFSMSMAFSMSMAFSMSMA
C**********ns******ns****
T************************
C*Tnsnsnsnsnsnsnsnsnsnsnsns
Note: C: cultivar; T: treatment; LIG: lignin; FS: flowering stage; MS: milk ripening stage; MA: maturity period. The ** indicate significant differences at 0.01 levels; ns indicates no statistical difference.
Table 4. Effects of drought stress at different growth stages on yield, stalk diameter and wall thickness of spring wheat under drip irrigation.
Table 4. Effects of drought stress at different growth stages on yield, stalk diameter and wall thickness of spring wheat under drip irrigation.
YearCultivarTreatmentThe Diameter of Internode (mm)Wall Thickness (mm)
Flowering StageMilk Maturity StageMaturity StageFlowering StageMilk Maturity StageMaturity Stage
2022XC22CK3.01 a2.81 b2.71 b1.26 ab1.32 b1.02 b
T13.31 a3.31 a2.99 ab1.42 ab1.51 a1.14 ab
T23.14 a3.02 ab2.87 ab1.23 b1.52 a1.12 ab
J13.39 a3.36 a3.16 a1.46 a1.64 a1.21 a
J23.18 a3.07 ab2.86 ab1.31 ab1.53 a1.11 ab
XC6CK3.11 b3.07 b2.85 b1.31 b1.53 b1.11 b
T13.41 ab3.37 ab3.11 ab1.48 ab1.66 ab1.24 ab
T23.23 b3.32 ab2.97 b1.36 ab1.61 ab1.22 b
J13.77 a3.72 a3.51 a1.56 a1.78 a1.31 a
J23.51 ab3.68 a3.48 a1.47 ab1.70 ab1.23 a
2023XC22CK3.11 b2.89 b2.79 b1.21 c1.28 b0.95 b
T13.31 ab3.38 a3.18 a1.43 ab1.55 ab1.16 a
T23.18 ab3.12 ab3.01 ab1.33 abc1.31 ab1.07 ab
J13.58 a3.45 a3.23 a1.49 a1.58 a1.18 a
J23.23 ab3.16 ab3.04 ab1.28 bc1.38 ab1.09 a
XC6CK3.15 c3.09 b2.93 b1.23 b1.47 b1.02 c
T13.50 b3.49 ab3.22 ab1.43 ab1.65 ab1.18 ab
T23.42 c3.28 ab3.01 ab1.37 ab1.61 ab1.11 bc
J13.89 a3.79 a3.55 a1.52 a1.73 a1.25 a
J23.63 b3.54 ab3.42 ab1.42 ab1.68 ab1.20 ab
FC************
T************
C*Tnsns*nsnsns
Note: C: cultivar; T: treatment. The * and ** indicate significant differences at 0.05 and 0.01 levels; ns indicates no statistical difference. Different lowercase letters indicate that different treatments of the variety have remarkable differences at 0.05 level.
Table 5. Effects of water stress at different growth stages on yield and composition of spring wheat under drip irrigation.
Table 5. Effects of water stress at different growth stages on yield and composition of spring wheat under drip irrigation.
YearCultivarTreatmentSpike Number
/(×104·ha−1)		Grain Number
per Spikes		1000-Grain
Weight (g)		Actual Yield
/(kg·ha−1)
2022XC22CK417.95 a36.21 a45.82 a6728.54 a
T1411.47 ab37.28 a46.37 a6920.70 a
T2376.87 b33.42 b44.36 a5283.62 b
J1413.20 a35.93 a45.17 a6453.69 a
J2408.74 a31.85 b39.82 b4663.67 c
XC6CK420.29 a36.73 ab46.25 ab6947.80 a
T1417.72 a38.40 a47.08 a7155.05 a
T2410.71 a35.60 b44.14 b6522.98 a
J1423.94 a37.59 ab46.49 ab6990.89 a
J2416.53 a32.93 c41.78 c5707.83 b
2023XC22CK424.38 a39.05 a46.42 ab7250.39 a
T1420.43 a39.06 a48.48 a7340.39 a
T2400.14 a36.64 b43.41 b6410.48 b
J1421.40 a38.13 ab46.01 bc6975.22 a
J2416.14 a34.32 c40.66 c5870.91 c
XC6CK430.13 a38.68 ab47.34 ab7149.28 a
T1425.73 a40.73 a48.44 a7577.03 a
T2414.21 a37.98 ab46.84 ab6649.24 b
J1428.82 a39.85 a47.49 a7231.34 a
J2419.08 a35.83 b43.12 b6162.95 c
Cns****
Tns******
C*Tnsnsnsns
Note: * and ** demonstrate remarkable differences at the 0.05 and 0.01 standards. ns indicates no statistical difference. Different lowercase letters indicate that different treatments of the variety have remarkable differences at 0.05 level.
Table 6. Path analysis of SC metabolism parameters, stalk diameter, wall thickness and wheat yield and its components at filling stage under different drought stress treatments at different stages.
Table 6. Path analysis of SC metabolism parameters, stalk diameter, wall thickness and wheat yield and its components at filling stage under different drought stress treatments at different stages.
Dependent VariableAction FactorCorrelation CoefficientPath CoefficientIndirect Path CoefficientsTotal
X1X5X7X9
Y1X5−0.314−0.314
Y2X1−0.054−0.398 −0.0540.1290.183
X7−0.135−0.318−0.043 0.1420.185
X90.3250.7190.234 0.321 0.555
Y3X5−0.269−0.296 0.0320.032
X90.2190.251 0.027 0.027
Y4X5−0.312−0.312
Notes: Y1: yield; Y2: spike number; Y3: grain number per spike; Y4: 1000-grain weight; X1: PAL; X5: H-type lignin; X7: S-type lignin; X9: stalk diameter. Action factor: The indicators with the highest impact on the dependent variables were filtered out by performing a linear regression on all indicators.
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MDPI and ACS Style

Zhang, Y.; Yin, H.; Wang, R.; He, F.; Jiang, G. Effects of Deficit Irrigation on Spring Wheat Lignification Process, Yield Productivity and Stalk Strength. Agronomy 2024, 14, 2647. https://doi.org/10.3390/agronomy14112647

AMA Style

Zhang Y, Yin H, Wang R, He F, Jiang G. Effects of Deficit Irrigation on Spring Wheat Lignification Process, Yield Productivity and Stalk Strength. Agronomy. 2024; 14(11):2647. https://doi.org/10.3390/agronomy14112647

Chicago/Turabian Style

Zhang, Yaoyuan, Haojie Yin, Rongrong Wang, Fangfang He, and Guiying Jiang. 2024. "Effects of Deficit Irrigation on Spring Wheat Lignification Process, Yield Productivity and Stalk Strength" Agronomy 14, no. 11: 2647. https://doi.org/10.3390/agronomy14112647

APA Style

Zhang, Y., Yin, H., Wang, R., He, F., & Jiang, G. (2024). Effects of Deficit Irrigation on Spring Wheat Lignification Process, Yield Productivity and Stalk Strength. Agronomy, 14(11), 2647. https://doi.org/10.3390/agronomy14112647

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