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Article

Straw Mulching Combined with Phosphorus Fertilizer Increases Fertile Florets of Wheat by Enhancing Leaf Photosynthesis and Assimilate Utilization

by
Wei Xie
1,2,
Peng He
1,2,
Hongliang Ma
1,2,
Xiulan Huang
1,2,
Gaoqiong Fan
1,2,3 and
Hongkun Yang
1,2,3,*
1
Agricultural College, Sichuan Agricultural University, Chengdu 611130, China
2
Crop Ecophysiology and Cultivation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
3
State Key Laboratory of Crop Gene Exploration and Utilization in Southwest China, Ministry of Science and Technology, Chengdu 611130, China
*
Author to whom correspondence should be addressed.
Agronomy 2023, 13(9), 2342; https://doi.org/10.3390/agronomy13092342
Submission received: 17 August 2023 / Revised: 5 September 2023 / Accepted: 7 September 2023 / Published: 8 September 2023
Browse Figures
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Abstract

:
Lack of soil moisture and phosphorus deficiency limits wheat grain yield in dryland areas. However, the moisture-conserving effect of straw mulching combined with phosphor fertilization on fertile florets per spike (FFS) and grain yield remains unclear. During the 2020–2021 and 2021–2022 growing seasons, we investigated the combined effects of straw mulching (0 and 8000 kg ha−1) and phosphorus fertilization (0, 75, and 120 kg P2O5 ha−1) on spike development, assimilates’ availability, and the photosynthetic properties of flag leaves by conducting a field experiment. Compared with no straw mulch control, straw mulching increased fertile spike, grain number per spike (15.6%), and grain yield (22.6%), and grain number per spike was the most important contribution to increasing wheat grain yield (46%). An increase in grain number per spike is associated with FFS. Compared with no straw mulch control, straw mulching increased FFS by 19.5%, and it increased with increasing phosphorus fertilization levels. Moreover, straw mulching combined with phosphorus fertilization promoted the light compensation point (LCP), light saturation point (LSP), net photosynthetic rate (Pn), Chl b, and the maximal photochemical efficiency of photosystem II (Fv/Fm) of flag leaves to produce carbohydrates. Our study has shown that the primary factor for the divergence in FFS under straw mulching and phosphorus application was the efficiency of assimilate utilization in the spike, which ultimately led to increased grain number per spike and grain yield.

1. Introduction

Wheat (Triticum aestivum L.) consumption is projected to increase exponentially to meet the demand of population growth [1]. Significant reductions in yield were associated with phosphorus deficiency and drought, which can be attributed to the reduction in grain number per unit land area [2], which is related to grain number per spike [3]. Soil drought during the stem extension stage of wheat accelerated the degradation and abortion of floret primordium, significantly decreasing the quality and quantity of floret development [4,5] and ultimately decreasing grain number per spike and grain yield. Phosphorus deficiency from the stage of anther septa formation to the stage of tetrad formation increased the number of degenerated florets [6,7]. Recent studies have shown that straw mulching conserves soil moisture for alleviating drought stress before anthesis and increases Olsen-P content during straw decomposition [8]. Many studies [9,10] have focused on the effects of P fertilization and straw mulching on fertile spikes. However, the combined effects of straw mulching and phosphorus fertilizer on grain number per spike and the underlying mechanism remain unclear.
Floret development can be divided into the differentiation and abortion of florets [11,12]. The maximum number of floret primordia (MFS) was usually observed at the W7.5 and was influenced by the genetic background of the cultivar and cultivation management, such as the nitrogen fertilization rate [13] and sowing date [2]. Fertile florets per spike (FFS) at anthesis presented a significant positive correlation with grain number per spike at maturity [14], which increases depending on the reduction in the degradation and abortion of floret primordium and the improvement in the survival of the floret primordium [1,15,16]. It has been shown that promoting MFS is a crucial way to increase floret survival [14].
The degradation and abortion of florets are closely related to carbohydrates, and most of the processes of floret development coincide with rapid stem and spike growth [13,14,17], which means rapid stem and spike growth probably competes with floret development for carbohydrates [2,5]. In addition, recent studies revealed that FFS significantly correlates with spike dry matter weight (DMW) at flowering [18,19]. Carbohydrates come from plant photosynthesis, and the flag leaf has generally been recognized as a significant contributor of photoassimilate to the developing stem, spike, and floret [20], mainly affecting source–sink relationships by influencing carbon assimilation and respiration rates, as well as the allocation and redistribution of carbon within the plant [21]. It has been proposed that straw mulching increases the net photosynthetic rate (Pn), maximum carboxylation rate, and stomatal conductance (Gs) in flag leaves [22], which are closely related to carbohydrates. Spike and floret development requires carbohydrates to remobilize from the source organ to the sink organ. However, the regime by which the photosynthesis and coordinate assimilate allocation relationship with floret development is established has yet to be clarified.
Our previous results revealed that straw mulching conserved soil moisture and alleviated drought stress before flowering. It also improved phosphorus availability and aboveground phosphorus uptake, finally increasing grain number per spike [23,24,25]. However, the mechanism underlying how straw mulching with phosphorus fertilization affects grain number per spike through floret development remains unclear. The present study aimed to: (a) evaluate the combined effects of straw mulching and phosphorus fertilizer on floret differentiation and degeneration; (b) examine the responses of flag leaf photosynthesis and carbohydrate competition between spike and stem on floret development. Our research was conducted based on the hypothesis that straw mulching combined with phosphorus improves the Pn of flag leaf and the utilization efficiency of assimilates in the spike, promoting floret development and increasing the number of grains set.

2. Materials and Methods

From 2020 to 2022, field experiments in Southwest China have been carried out at the Renshou experimental station (33°19′ N, 120°45′ E). The research station was established in the typical dryland farming system. According to official recommendations, the soil nutrition of wheat was found to be high in mineral K (138 mg kg−1), but poor in organic matter (15.8 g kg−1), alkali–hydrolyzable N (56.5 mg kg−1), and Olsen–P (6.4 mg kg−1) in the 0–20 cm layer. The mean air temperature and precipitation were 17.9 °C and 292.6 mm during wheat growth (Figure 1). As shown in Figure 1, the rainfall from sowing to anthesis was continuously low. In the experiment region, winter wheat–summer maize were the most typical rotation systems, and maize straw was utilized to cover fields where wheat is grown. Therefore, straw mulching was employed to alleviate soil drought and improve fertility [23,24,25].

2.1. Experimental Design and Field Management

Straw mulch was used as the primary factor in the split-plot experiment, while the phosphorus level was used as a subplot factor, with three 10.2 m2 (3 m × 3.4 m) duplications per treatment. Crop residue removal was used for no straw mulch control. After the maize harvest in late August, crushed stalks were used as mulch. Application rates for straw mulch were 0 (NSM, no straw mulching) and 8000 (SM, straw mulching) kg ha−1. Wheat was grown at three P levels: 0 (P0), 75 (P75), and 120 (P120) kg P2O5 ha−1. Chuanmai39 (CM–39), known as a high-yield winter wheat, was sown on Oct–30. Standard urea was used as the nitrogen fertilizer (N 46.2%), calcium superphosphate as the phosphorus fertilizer (P2O5 12.5%), and potassium chloride as the potash fertilizer (K2O 60.0%). The nitrogen and potash fertilizers levels were 150 and 75 kg ha−1, respectively. The basal fertilizers included 60% of the nitrogen fertilizers and all of the phosphorus and potash fertilizers, and the remaining nitrogen fertilizers were used at the stem extension stage. This experiment did not use irrigation to reflect the straw mulching effect. In order to reduce yield loss, commercial herbicides, insecticides, and fungicides were applied proactively each month after tillering, which was performed according to local management procedures.

2.1.1. Grain Yield and Yield Components

Fertile spike, grain number, and grain weight were measured at mature stage. We harvested all plants within a tested area of 0.6 m2 × 6 rows (3.6 m2) to estimate the grain yield.

2.1.2. Spike Differentiation Characteristics

At the floret development stage of W5.5, W6.5, W7.5, W8.5, W9.5, and W10 based on Waddington’s scale, five main shoots with similar growth and development from each subplot were picked in 2021–2022, and their young spikes were separated and examined with a microscope (SOPTOP SZN71). The growth of the first floret in the center of the spikelets can be used to estimate the period of floret development, and the number of living floret primordia (NFS) was recorded [12]. Usually, NFS at W10 were considered FFS (florets with whole stigmatic hair and green anthers).

2.1.3. DMW and Carbohydrate Contents

Fifteen main shoots with similar growth were picked in each subplot at each floret development stage to separate into leaf, stem, and spike, which were afterward dried at 75 °C to constant weight. The anthrone method measured the water-soluble carbohydrates (WSC) [26]. The KOH-resorcinol method measured the sucrose content [27].

2.1.4. Photosynthetic Parameters, Chlorophyll Fluorescence Parameters, and Chlorophyll Content

At the W10 stage, a photosynthesis system Li–6800 (Li–COR, Lincoln, NE, USA) was applied to measure photosynthetic parameters and photosynthetic light-response curves on the flag leaf. Photosynthetic light-response curves were fitted using a nonlinear hyperbolic model as follows:
( P n I = α I + P n m a x − α I + P n m a x α I + P n m a x   −   4 α I P n m a x 2 θ   −   R n )  
where α is the apparent quantum yield (AQY), I denotes the photosynthetic photon flux density (PPFD), and maximum net photosynthetic rate (Pnmax) is the maximum net photosynthesis rate. Rn is the rate of dark respiration [28]. The conditions were 1200 μmol m−2 s−1 quantum flux and 400 ± 5 μmol m−2 s−1 CO2 concentration. Pn (net photosynthetic rate) was recorded at PPFD values of 2000, 1800, 1600, 1400, 1200, 1000, 800, 600, 400, 200, 100, 50, and 0 μmol m−2 s−1.
At the same time, a PAM–2500 fluorometer (Heinz Walz GmbH, Effeltrich, Germany) was applied to measure chlorophyll fluorescence parameters of the same leaves. Photochemical efficiency, photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were measured according to Zou [29]. After completing the above steps, the leaves were quickly cut and used Anhydrous ethanol to extract chlorophyll [30]. The ratio of Pn to Transpiration rate (E) was employed for calculating the instantaneous WUE (WUEins) from the gas exchange date from the flag leaf [31].

2.2. Statistical Analysis

IBM SPSS statistics (version 26.0, IBM Corp., Armonk, NY, USA) was applied to analyze variance (ANOVA) for the split-plot design. A least-significant difference (LSD) at a probability threshold of p < 0.05 or p < 0.01 was used to evaluate mean values for significant differences. We used Stata MP 17 to analyze the contribution of yield composition to yield. All figures shown in our study were generated in Origin (2021 b, Origin Lab, Northampton, MA, USA).

3. Results

3.1. Grain Yield and Yield Components

The ANOVA revealed that grain yield and grain number per spike were significantly affected by year, phosphorus, straw mulching, and the interaction of phosphorus fertilizer and straw mulching (Table 1). Compared with no straw mulch control, straw mulching increased grain yield by 22.6%. Grain yield increased by 17.9–23.1% at different phosphorus fertilizer levels compared with no phosphorus control. Grain yield increased with increasing phosphorus fertilizer, and phosphorus application exceeding 75 kg ha−1 did not increase grain yield. Compared with no straw mulch control, straw mulching increased grain number per spike by 15.6%. At different phosphorus fertilizer levels, grain number per spike increased by 9.1–11.6%. Moreover, the 1000-kernel weight is not affected by straw mulching and phosphorus fertilizer. Dominant analysis showed that fertile spikes and grain number per spike contribute to 89% of total yield variations (Figure 2). Grain yield increased with increasing grain number per spike (R2 = 0.98 **).

3.2. Spike Differentiation Characteristics

The patterns of floret primordium differentiation and degradation are shown in Figure 3. The trend was similar among all treatments; the living floret primordium numbers increased quickly until they reached W7.5 and peaked (W5.5–W7.5), followed by a rapid degeneration and abortion of various florets (W8.5–W10). In contrast, only the rest of the florets progressed normally to achieve fertility. From W7.5 to W8.5, living floret primordium decreased by 60.2–66.4%. Compared with the no straw mulch control, straw mulching increased FFS by 19.5%, and FFS increased with increasing phosphorus levels. NFS and FFS were positively related to grain number per spike (R2 = 0.66 **, R2 = 0.86 **, Figure 4).

3.3. Water-Soluble Carbohydrate and Sucrose Contents

To explore how stem growth affects spike development, the WSC and sucrose content of the leaf, stem, and spike were measured at W7.5 and W10 (Figure 5). The spike and stem DMW showed a more rapid increase at W10 than at W7.5 (Figure 5A,B), while the WSC and sucrose content of spike showed opposite trends (Figure 5G,H), but stem remained almost unchanged (Figure 5E,F). Compared with the no straw mulch control, spike and stem DMW were significantly higher in straw mulching. Moreover, spike DMW increased with increasing levels of phosphorus application (Figure 5A,B). However, compared with no straw mulch control, straw mulching decreased the WSC and sucrose content and decreased with increasing phosphorus fertilizer (Figure 5C–H). These results indicated that spike development was the primary physiological activity in wheat during W7.5 and W10. A large portion of the WSC and sucrose in the spike were utilized to form spike morphology, thereby reducing the availability of assimilates for floret development and increasing floret degeneration and abortion with programmed cell death.
The dry matter weight of the spike and stem related to the WSC and sucrose content were further analyzed. The WSC and sucrose content of the leaf were not related to stem and spike DMW (Figure 6A,B). Moreover, there was a significant negative correlation between the WSC and sucrose content of the stem and stem DMW, and the spike showed the same trend. The WSC and sucrose content of the stem was not related to spike DMW, but the WSC and sucrose content of the spike were more related to stem DMW (Figure 6C–F), which also proved a competitive relationship between stem elongation and rapid spike growth. In addition, NFS was significantly positively correlated with spike and stem DMW (Figure 6G,H).

3.4. Photosynthetic Parameters, Chlorophyll Content, and Chlorophyll Fluorescence Parameters

Results based on the rectangular hyperbolic curve are shown in Figure 7. As with the results in Table 2, straw mulching and phosphorus application significantly affected the Pnmax, light compensation point (LCP), and light saturation point (LSP), but no interaction was observed. Compared with the no straw mulch control, Pnmax was higher in straw mulching and increased with increasing phosphorus levels. Straw mulching and phosphorus application significantly affected the Pn and E of the flag leaf. WUEins were not affected by phosphorus application. In contrast, the Gs of flag leaves were hardly affected by straw mulching, but increased dramatically in the phosphorus application treatment and were higher in the 120 kg P2O5 ha−1 treatment. Compared with the no straw mulch control, intercellular CO2 concentration (Ci) was higher in straw mulching. The flag leaf Chl a and Chl b contents were increased by 5.3–6.4% and 3.8–6.3%, respectively, under phosphorus application treatments. The photochemical efficiency of photosystem II (ΦPSII) and the maximal photochemical efficiency of photosystem II (Fv/Fm) of flag leaves were significantly reduced in the 0 kg P2O5 ha−1 treatment and increased by 25.0–27.9% and 9.9–10.4% under phosphorus application (Table 3).
We analyzed the relationship between photosynthetic parameters, FFS, and grain number per spike based on the above photosynthetic characteristics. FFS was significantly positively related to LCP, LSP, Pn, Chl b, Fv/Fm, and grain number per spike; significantly positively related to LSP, E, and Chl a; but there was a negative correlation with WUEins (Table 4).

4. Discussion

4.1. The Utilization Efficiency of Assimilates Was Mainly a Limiting Factor for the FFS

Soil drought and phosphorus deficiency decrease grain number per spike and grain yield [32,33], which are typically related to sink restrictions [34]. Our study showed that straw mulching with phosphorus application fertilizer increased wheat yield, mainly attributed to increased grain number per spike (Table 1, Figure 2), agreeing with the results obtained for delayed sowing [17] and nitrogen fertilization [14]. Increased grain number per spike can be attributed to the soil-moisture-conserving effect of straw mulching, which alleviates dough stress during spike differentiation and ultimately increases the survival of florets and grain number per spike [35]. Another possible explanation is that straw decomposition increased P availability in the soil, promoting phosphorus uptake by wheat root [36], with increasing dry matter accumulation and grain yield [37]. MFS and FFS are critical in determining the grain number per spike [2,38]. Our study found that straw mulching and phosphorus application significantly increased MFS and FFS, positively related to grain number per spike (Figure 3 and Figure 4). These results are consistent with previous studies [15,39].This may be because of increasing the number of florets with green anthers and floret survival [14]. Another possible explanation is extending the period of the double ridges stage of spike differentiation duration, which will form more spikelet positions and NFS. Previous studies have proved that straw mulching can delay wheat fertility [40], which benefits from prolonging the duration of the double ridges stage to form more spikelets. In addition, straw mulching makes wheat plants thrive [41], which benefits providing a sufficient carbohydrate supply for the development of florets.
A novel finding is that the WSC and sucrose contents in spikes were higher in the no straw mulch control (Figure 6). However, they did not promote increased FFS and grain number per spike (Figure 3, Table 1). This may be because more soluble nonmetabolic sugars are produced and entered into vacuoles to maintain cell osmotic potential to resist drought [42,43]. These results showed that the utilization efficiency of assimilates was mainly a limiting factor for the FFS during stem elongation and rapid spike growth.

4.2. Increased Photosynthetic Efficiency of Flag Leaves, Which Promoted the Supply of Sources for Spike Development

The photosynthesis of flag leaves is crucial in grain number per spike [44]. Previous studies have proved that drought and phosphorus deficiency reduced photosynthesis [29], thereby affecting photoassimilate production [20], which may limit spike growth and development, including spike formation and floret development. As a significant source of sucrose, photosynthesis is one of the critical processes affected by straw mulching with phosphorus application, and this is because any reduction in CO2 diffusion or utilization will directly lead to a reduction in the rate of photosynthesis [45,46,47].
A novel finding is that Ci and Pn were reduced in the no straw mulch control, indicating that the reduction in Pn was mainly caused by the stomata (Table 3). This may be because porosity is reduced owing to drought, which limits the diffusion of CO2 into the interstitial space, reducing stomatal conductance and Pn [48]. Interestingly, the Fv/Fm and photosystem II of flag leaves were significantly reduced in the 0 kg P2O5 ha−1 treatment, indicating that the decrease in Fv/Fm and photosystem II quantum efficiency was also a nonstomatal factor contributing to the decrease in Pn. (Table 3) Thus, drought and phosphorus deficiency reduced the proportion of photosystem II reaction centers and lowered the level of photosynthetic activity [49,50]. The correlation analysis showed that straw mulching and phosphorus application promoted the LCP, LSP, Pn, Chl b, and Fv/Fm of flag leaves to affect the development of FFS (Table 4). This may be because these indicators promote the photosynthesis of flag leaves to increase carbohydrates [20]. Most of the research focused on flag leaf photosynthesis in wheat after flowering. However, understanding and assessing earlier photosynthetic efficiency might be of greater importance to optimize spikelet and floret fertility [44].

5. Conclusions

Straw mulching combined with phosphate fertilizer increased the fertile spikes, grain number per spike (15.6%), and grain yield (22.6%) of wheat, and grain number per spike had the most important contribution to increasing wheat grain yield (46%). Straw mulching with phosphorus application promotes the Pn of flag leaves to increase carbohydrates and improve the utilization efficiency of assimilates in spike for floret development, finally increasing FFS and grain yield (Figure 8). These results showed that the utilization efficiency of assimilates was mainly a limiting factor for the FFS during stem elongation and rapid spike growth. The results of this study could provide a new theoretical basis and technical support to achieve high-yield cultivation of dryland wheat. However, it remains to be verified whether straw mulching combined with phosphate fertilizer affects nitrogen absorption and accumulation and carbon and nitrogen metabolism enzymes during floret development.

Author Contributions

W.X.: conceptualization, methodology, field management, data collection, curation, and writing. P.H.: field management, data collection, and curation. H.M.: conceptualization, methodology, field management, and data collection. X.H.: writing—review and editing and management. G.F. and H.Y.: funding acquisition, conceptualization, methodology, writing—review and editing, and supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Nature Science Foundation of China (32201904), the Sichuan Science and Technology Support Program (2022ZDZX0014), the Crops Breeding Project in Sichuan Province (22ZDZX0018), and the Sichuan Key Research and Development Program (2021YFYZ0002).

Data Availability Statement

All data supporting the findings of this study are available within the paper.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Abbreviations

SM: straw mulching; NSM: no straw mulching; P0: 0 kg P2O5 ha−1; P75: 75 kg P2O5 ha−1; P120: 120 kg P2O5 ha−1; NFS: the number of living floret primordia; MFS: the maximum number of living floret primordia; FFS: fertile florets per spike; WSC: water-soluble carbohydrates; DMW: dry matter weight; AQY: apparent quantum yield; PPFD: photosynthetic photon flux density; Pn: net photosynthetic rate; Pnmax: maximum net photosynthetic rate; Gs: stomatal conductance; qP: photochemical quenching coefficient; qN: non-photochemical quenching coefficient; E: Transpiration rate; LCP: light compensation point; LSP: light saturation point; Ci: intercellular CO2 concentration; ΦPSII: photochemical efficiency of photosystem II; Fv/Fm: maximal photochemical efficiency of photosystem II; WUEins: instantaneous WUE.

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Figure 1. Daily air temperature (°C) and precipitation (mm) recorded during two growing seasons (2020–2021 and 2021–2022) of winter wheat.
Figure 1. Daily air temperature (°C) and precipitation (mm) recorded during two growing seasons (2020–2021 and 2021–2022) of winter wheat.
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Figure 2. Analysis of the contribution of yield components to yield (A) and the relationship between grain number per spike and yield (B). n = 36. **, p < 0.01.
Figure 2. Analysis of the contribution of yield components to yield (A) and the relationship between grain number per spike and yield (B). n = 36. **, p < 0.01.
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Figure 3. Effect of no straw mulch (A) and straw mulching (B) combined with phosphorus fertilizer on number of living floret primordia (NFS). Data in each treatment present all values for 2021–2022. n = 18. Vertical bars denote standard error (n = 3). Significance was only compared using P0 versus P75. *, p < 0.05; **, p < 0.01; *** p < 0.001.
Figure 3. Effect of no straw mulch (A) and straw mulching (B) combined with phosphorus fertilizer on number of living floret primordia (NFS). Data in each treatment present all values for 2021–2022. n = 18. Vertical bars denote standard error (n = 3). Significance was only compared using P0 versus P75. *, p < 0.05; **, p < 0.01; *** p < 0.001.
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Figure 4. Number of living floret primordia at W7.5 correlated with W10 (A), number of living floret primordia at W7.5 (B) and W10 (C) correlated with grain number per spike. Data in each treatment present all values for 2021–2022. n = 18. **, p< 0.01.
Figure 4. Number of living floret primordia at W7.5 correlated with W10 (A), number of living floret primordia at W7.5 (B) and W10 (C) correlated with grain number per spike. Data in each treatment present all values for 2021–2022. n = 18. **, p< 0.01.
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Figure 5. Effect of straw mulching combined with phosphorus fertilizer on the dry matter weight (A,B), water-soluble carbohydrates, and sucrose contents in leaf (C,D), stem (E,F), and spike (G,H) at W7.5 and W10. Different letters indicate significant differences (p < 0.05) among treatments according to LSD. Data in each treatment present all values for 2021–2022.
Figure 5. Effect of straw mulching combined with phosphorus fertilizer on the dry matter weight (A,B), water-soluble carbohydrates, and sucrose contents in leaf (C,D), stem (E,F), and spike (G,H) at W7.5 and W10. Different letters indicate significant differences (p < 0.05) among treatments according to LSD. Data in each treatment present all values for 2021–2022.
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Figure 6. Dry matter weight correlated with water-soluble carbohydrates, sucrose, and number of living floret primordia at W7.5 (MFS) and W10 (FFS). Data in each treatment present all values for 2021–2022. n = 36 for (A–F) and n = 18 for (G,H). **, p < 0.01.
Figure 6. Dry matter weight correlated with water-soluble carbohydrates, sucrose, and number of living floret primordia at W7.5 (MFS) and W10 (FFS). Data in each treatment present all values for 2021–2022. n = 36 for (A–F) and n = 18 for (G,H). **, p < 0.01.
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Figure 7. Effect of no straw mulch (A) and straw mulching (B) combined with phosphorus fertilizer on Pn in response to PPFD in the flag leaf at W10 in 2021. Data in each treatment present all values for 2021–2022. Each point represents the mean value of three replications ± standard error.
Figure 7. Effect of no straw mulch (A) and straw mulching (B) combined with phosphorus fertilizer on Pn in response to PPFD in the flag leaf at W10 in 2021. Data in each treatment present all values for 2021–2022. Each point represents the mean value of three replications ± standard error.
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Figure 8. Cause and effect model illustrating how straw mulch and P fertilizer regulate utilization efficiency of assimilates and flag leaf photosynthesis in developing spike. Red arrows represent rising.
Figure 8. Cause and effect model illustrating how straw mulch and P fertilizer regulate utilization efficiency of assimilates and flag leaf photosynthesis in developing spike. Red arrows represent rising.
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Table 1. Effects of straw mulching, P fertilizer, year, and their combination on yield components and yield during wheat growth periods in 2020–2022.
Table 1. Effects of straw mulching, P fertilizer, year, and their combination on yield components and yield during wheat growth periods in 2020–2022.
YearTreatmentFertile Spike
(×104 ha−1)		Grain Number
per Spike		1000-Kernel Weight
(g)		Grain Yield
(kg ha−1)
2020–2021NSMP0288 ± 8 d35.6 ± 0.9 d48.3 ± 0.2 a4209 ± 215 c
P75303 ± 9 bc37.7 ± 0.7 c48.4 ± 0.2 a4701 ± 160 b
P120312 ± 3 b39.1 ± 0.6 bc48.5 ± 0.1 a5039 ± 94 b
SMP0300 ± 3 c39.8 ± 1.1 b48.4 ± 0.3 a4915 ± 142 b
P75338 ± 2 a44.7 ± 1.0 a48.3 ± 0.2 a6199 ± 121 a
P120339 ± 7 a44.9 ± 0.7 a48.7 ± 0.1 a6292 ± 190 a
2021–2022NSMP0284 ± 9 d34.3 ± 0.2 d48.4 ± 0.3 a4006 ± 103 d
P75300 ± 8 cd36.1 ± 0.4 c48.5 ± 0.9 a4453 ± 157 c
P120308 ± 2 bc38.1 ± 0.7 b48.3 ± 0.1 a4825 ± 61 bc
SMP0292 ± 7 d38.8 ± 0.7 b48.2 ± 0.1 a4644 ± 172 bc
P75314 ± 2 ab43.5 ± 0.6 a48.2 ± 0.2 a5596 ± 84 a
P120322 ± 4 a43.6 ± 0.6 a48.0 ± 0.1 a5730 ± 154 a
Year (Y)** ** ns **
Straw mulch (S)** ** ns **
P fertilizer (P)** ** ns **
Y × S** ns ns *
Y × Pns ns ns ns
S × P* ** ns **
Y × S × Pns ns ns ns
Note: Values represent means ± SD (n = 3). Different letters indicate significant differences (p < 0.05) among treatments according to LSD. SM, straw mulching; NSM, no straw mulching; P0, 0 kg P2O5 ha−1; P75, 75 kg P2O5 ha−1; P120, 120 kg P2O5 ha−1. *, p < 0.05; **, p < 0.01. ns, non-significant.
Table 2. Effects of straw mulch, P fertilizer, and their combination on photosynthetic light-response curve parameters in wheat flag leaves in 2021–2022.
Table 2. Effects of straw mulch, P fertilizer, and their combination on photosynthetic light-response curve parameters in wheat flag leaves in 2021–2022.
TreatmentPnmax
(μmol CO2 m–2 s−1)		AQY
(mol mol−1)		LCP
(μmol m–2 s−1)		LSP
(μmol m–2 s−1)
NSMP024.1 ± 0.3 d0.066 ± 0.002 a16.0 ± 1.5 d1206 ± 28 c
P7525.4 ± 0.2 c0.067 ± 0.003 a18.0 ± 0.0 c1341 ± 81 b
P12025.9 ± 0.5 bc0.068 ± 0.001 a20.4 ± 1.7 bc1385 ± 78 b
SMP025.6 ± 0.4 c0.070 ± 0.005 a21.7 ± 0.1 b1397 ± 42 b
P7526.7 ± 0.6 b0.067 ± 0.002 a26.4 ± 1.5 a1716 ± 49 a
P12028.8 ± 0.5 a0.068 ± 0.001 a27.7 ± 0.4 a1717 ± 31 a
Significance of factors
Straw mulch (S)**ns****
P fertilizer (P)* ns * **
S × Pns nsnsns
Note: Values represent means ± SD (n = 3). Different letters indicate significant differences (p < 0.05) among treatments according to LSD. *, p < 0.05; **, p < 0.01. ns, non-significant.
Table 3. Effect of straw mulch, P fertilizer, and their combination on photosynthetic characteristics in wheat flag leaves at W10 in 2021–2022.
Table 3. Effect of straw mulch, P fertilizer, and their combination on photosynthetic characteristics in wheat flag leaves at W10 in 2021–2022.
TreatmentPn
(µmol m−2 s−1)		E
(µmol m−2 s−1)		Gs
(mol m−2 s−1)		Ci
(µmol m−2 s−1)		Chl a
(mg/g)		Chl b
(mg/g)		ΦPSIIFv/FmWUEins
(µmol/mmol)
NSMP022.5 ± 0.2 c4.55 ± 0.26 c0.32 ± 0.00 c247 ± 4.3 d1.69 ± 0.07 b0.57 ± 0.04 c0.31 ± 0.00 f0.69 ± 0.00 d4.97 ± 0.31 a
P7523.0 ± 0.2 c4.73 ± 0.15 bc0.37 ± 0.00 b251 ± 3.8 cd1.87 ± 0.05 a0.62 ± 0.01 b0.42 ± 0.00 c0..76 ± 0.00 c4.86 ± 0.16 a
P12023.8 ± 1.2 bc4.77 ± 0.10 bc0.38 ± 0.03 ab253 ± 1.9 bc1.91 ± 0.01 a0.66 ± 0.04 ab0.44 ± 0.00 b0.76 ± 0.00 c4.99 ± 0.35 a
SMP023.4 ± 0.7 c4.95 ± 0.11 b0.36 ± 0.03 b257 ± 2.5 ab1.88 ± 0.02 a0.66 ± 0.03 ab0.40 ± 0.00 d0.77 ± 0.01 d4.79 ± 0.09 a
P7524.9 ± 0.3 ab6.06 ± 0.02 a0.38 ± 0.01 ab258 ± 0.6 a1.89 ± 0.01 a0.70 ± 0.00 a0.47 ± 0.00 a0.84 ± 0.00 a4.11 ± 0.05 b
P12025.3 ± 0.7 a6.15 ± 0.12 a0.41 ± 0.00 a262 ± 1.3 a1.89 ± 0.05 a0.71 ± 0.00 a0.48 ± 0.00 a0.85 ± 0.01 a4.12 ± 0.19 b
Significance of factors
Straw mulch (S)*** ns ************
P fertilizer (P)**** ns* * ** **ns
S × Pns ns ns ns *ns ** nsns
Note: Values represent means ± SD (n = 3). Different letters indicate significant differences (p< 0.05) among treatments according to LSD. *, p < 0.05; **, p < 0.01. ns, non-significant.
Table 4. Correlation between photosynthetic parameters and fertile florets and grain number per spike for growing seasons of 2021–2022.
Table 4. Correlation between photosynthetic parameters and fertile florets and grain number per spike for growing seasons of 2021–2022.
VariablePnmaxAQY LCPLSPPnEGsCiChl aChl bΦPSIIFv/FmWUEins
Fertile florets0.89 *0.27 *0.99 **0.99 **0.97 **0.94 *0.88 *0.94 *0.760.97 **0.93 *1.00 **−0.93
Grain number per spike0.78−0.940.981.00 **0.981.00*0.810.671.00 *0.990.990.99−1.00 *
Note: *, p < 0.05; **, p < 0.01.
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Xie, W.; He, P.; Ma, H.; Huang, X.; Fan, G.; Yang, H. Straw Mulching Combined with Phosphorus Fertilizer Increases Fertile Florets of Wheat by Enhancing Leaf Photosynthesis and Assimilate Utilization. Agronomy 2023, 13, 2342. https://doi.org/10.3390/agronomy13092342

AMA Style

Xie W, He P, Ma H, Huang X, Fan G, Yang H. Straw Mulching Combined with Phosphorus Fertilizer Increases Fertile Florets of Wheat by Enhancing Leaf Photosynthesis and Assimilate Utilization. Agronomy. 2023; 13(9):2342. https://doi.org/10.3390/agronomy13092342

Chicago/Turabian Style

Xie, Wei, Peng He, Hongliang Ma, Xiulan Huang, Gaoqiong Fan, and Hongkun Yang. 2023. "Straw Mulching Combined with Phosphorus Fertilizer Increases Fertile Florets of Wheat by Enhancing Leaf Photosynthesis and Assimilate Utilization" Agronomy 13, no. 9: 2342. https://doi.org/10.3390/agronomy13092342

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