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Article

Sink Strength Governs Yield Ceiling in High-Yield Cotton: Compensation Effects of Source–Sink Damage and Reproductive Stage Regulation

by
Zhenwang Zhang
1,
Kexin Li
1,
Qinghua Liao
1,
Zhijie Shi
1,
Keke Yu
2,*,
Junqi Zhu
3,
Xiyu Jia
1,
Guodong Chen
4,
Sumei Wan
4,
Shanwei Lou
5,
Mingfeng Yang
3,
Fangjun Li
1,
Xiaoli Tian
1,
Zhaohu Li
1 and
Mingwei Du
1,4,5,*
1
Engineering Research Center of Plant Growth Regulator, Ministry of Education, State Key Laboratory of Plant Environmental Resilience, College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, China
2
Key Laboratory of Tobacco Biology and Processing, Ministry of Agriculture and Rural Affairs, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao 266101, China
3
Wulanwusu Agrometeorological Experiment Station, Wulanwusu Ecology and Agrometeorology Observation and Research Station of Xinjiang, Wulanwusu Special Test Field base of National Integrated Meteorological Observation, Shawan 832199, China
4
Key Laboratory of Genetic Improvement and Efficient Production for Specialty Crops in Arid Southern Xinjiang of Xinjiang Corps, College of Agriculture, Tarim University, Alar 843300, China
5
Cotton Research Institute of Xinjiang Uyghur Autonomous Region Academy of Agricultural Sciences, National Cotton Engineering Technology Research Center, Urumqi 830091, China
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(9), 2099; https://doi.org/10.3390/agronomy15092099
Submission received: 29 July 2025 / Revised: 24 August 2025 / Accepted: 27 August 2025 / Published: 30 August 2025
(This article belongs to the Special Issue Crop Productivity and Management in Agricultural Systems)
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Abstract

Under refined management, high-yield cotton fields are approaching their maximum output. However, how to break this yield upper limit, specifically the source–sink relationship is still inadequately researched. This experiment was conducted to explore the interaction mechanism between yield formation and source–sink parameters (photosynthesis, nitrogen content, canopy structure and dry matter accumulation and distribution). The treatments consisted of a no cutting source and sink treatment (CK), cutting 1/2 leaves per plant (1/2L) and cutting 1/2 bolls per plant (1/2B) at the initial flowering stage (IFS), the flower and boll stage (FABS), and the full boll stage (FBS). The results showed that 1/2L treatment minimized yield losses to 2.3–5.9% by enhancing photosynthetic compensation, with FBS-1/2L showing the smallest reduction (2.3–2.9%) due to higher leaf N content and SPAD values, whereas, the 1/2B treatments resulted in significant yield losses attributable to fewer bolls, especially the FBS-1/2B treatments, which reduced yields by 35.7–41.9%, with a compensatory rate of only 8.1–14.3%. It is noteworthy that the compensation rates of IFS-1/2B and FABS-1/2B could reach 26.7–32.3% and 18.7–23.8% of their yields due to the higher leaf N content. In a word, the source damage can be buffered by physiological compensation, while the sink loss leads to yield collapse due to the irreversibility of reproductive development. Thus, the core regulator of high-yield cotton fields was sink strength. Accordingly, optimizing the sink quality was performed through moderate boll thinning at the IFS, enhancing water and fertilizer supply at the FABS and strengthening sink organ protection at the FBS in order to realize a breakthrough in yield limit.

1. Introduction

Xinjiang has become a major cotton-growing area and China’s largest cotton-producing region. Therefore, increasing cotton production in this region is of great significance [1]. As an important theoretical basis for crop yield physiology research, the source–sink theory has an important guiding value for yield formation [2]. The theory emphasizes the collaborative relationship between the source organs (photosynthetic product production), sink organs (product storage), and the material transport system between them. Specifically, this is reflected in the material supply capacity of the source organs, the storage capacity of the sink organs, and the efficiency of material transport between the source and sink [3]. It is noteworthy that the same organ may serve dual functions, such as developing leaves, which are both a source of carbon assimilation products and a sink for nitrogen assimilation [4]. Cotton, as a typical economic crop, has its seed cotton yield composed of both fiber and seed. Among them, fiber, as the primary harvesting organ, primarily depends on photosynthetic carbon metabolism for its formation, while cotton seeds are rich in protein (content ranging from 30% to 50%), making them an important source of plant protein [5]. The leaves, as the main source organs, require a large amount of nitrogen for the photosynthesis process: key proteins such as the Photosystem II complex and Rubisco enzyme account for approximately 50% of the nitrogen distribution in the leaf. This nitrogen investment strategy results in a significant positive correlation between the leaf’s photosynthetic capacity and its nitrogen content [6,7]. This metabolic characteristic determines the dual role of nitrogen in cotton growth and development—both as the essential element for constructing photosynthetic machinery and as a limiting factor in yield formation [8]. Therefore, the efficient use of nitrogen in cotton cultivation management has become a key regulatory target for achieving high-quality, high-yield production.
Cao et al. [9] categorized the source–sink types of rice varieties into three types in their study: source-limited, sink-limited, and source–sink-interaction types. The source–sink characteristics vary for each type. However, under stress conditions, crops may undergo a shift in their source–sink relationships. For instance, rice exhibits a shift toward a source-limited state under high-temperature stress [10], whereas wheat becomes sink-limited under similar conditions [11]. Similarly, cotton tends to shift to a source-limited state under salt stress [12,13], while drought stress often induces a sink-limited state in various crops [14]. In practical agricultural settings, crops are frequently exposed to unavoidable abiotic stresses, which disrupt the dynamic equilibrium of the source–sink relationship. Maintaining a balanced source–sink relationship is critical for achieving high crop yields [15]. Under the high-density planting pattern in Xinjiang cotton fields, excessive population leaf area readily induces mutual shading of canopy leaves [16], thereby reducing photosynthetic efficiency. Consequently, the conventional source–sink theory predominantly focuses on “source limitation” regulation, aiming to enhance canopy light distribution by optimizing morphological parameters such as leaf number, leaf area index (LAI), and leaf inclination angle (MTA) to achieve yield improvement [17,18]. However, studies have found that the number of bolls per plant and the weight of each boll in high-yield cotton fields were significantly higher than those low-yield fields [19]. Therefore, in order to maintain stable yield in high-yield cotton fields, more attention should be paid to “sink limitation”.
Leaves and bolls, as the main entities of the “source” and “sink” of cotton, this relationship reflects the coordinated role of cotton in the process of vegetative growth and reproductive growth [20]. During the growth and development of crops, the source–sink relationship continuously evolves and coordinates, with the final balance being fundamental to achieving high yield. The boll/leaf ratio can be used as an index to reflect the source–sink relationship of the cotton population [21]. In the study of the cotton source–sink relationship, traditional experimental methods primarily manipulate the source–sink ratio by artificially removing leaves or reproductive organs (e.g., fruit branches and bolls) [22,23]. It is important to note that plants exhibit nonlinear responses to defoliation stress, with different levels of stress intensity inducing differentiated compensatory growth effects. These compensatory effects can be classified into three categories: overcompensation, equal compensation, and under compensation [24]. The intensity of this effect is significantly negatively correlated with the degree of defoliation stress, and there are notable inter-species differences. For example, Mo et al. [25] found that removing 75% of the leaves did not significantly impact cotton yield. Wilson et al. [26] showed that when the main stem leaves were removed before the bud formation stage, cotton yield was not greatly affected, as the plant recovered well over time. Additionally, reproductive organs also exhibit compensatory plasticity [27]. Studies have shown that removing some of the early young buds could increase the fruit-set rate of the remaining fruit branches without reducing the yield [28,29]. This might be due to the fact that cotton removes the early fruit tissues, and compensates for it by increasing the number of buds and bolls on the upper main stem nodes [30]. Some studies have reported that the removal of the flower-bud and boll sink reduces the capacity of the sink, which in turn decreases the photosynthetic rate of cotton, obstructs the output of assimilates, reduces sucrose synthesis, and ultimately leads to a decrease in yield [31]. These findings highlight the complex compensatory regulatory mechanisms within the cotton source–sink system at the organ level. However, existing studies have largely focused on the compensatory mechanisms during a single developmental stage of cotton, while the dynamic changes in compensatory capacity across different growth stages and their regulatory effects remain unclear.
We hypothesize that the upper limit of the yield of high-yield cotton fields is the sink strength. Therefore, the objectives of this study were (a) to determine whether the regulation of source–sink in high-yield cotton fields has shifted from “source limitation” to “sink limitation” and (b) to explore the dynamic changes in cotton’s self-compensatory capacity across different growth stages under altered source–sink conditions.

2. Materials and Methods

2.1. Study Site

A two-year field experiment was conducted from 2023 to 2024 at the Wulanwusu Agrometeorological Station (44°17′ N, 85°49′ E) in Shihezi, Xinjiang Province, China. The soil in the experimental site was a clay loam with a total N concentration of 1.0 g·kg−1, available P of 15.9 mg·kg−1, available K of 162.8 mg·kg−1, a pH of 8.3 and organic matter of 15.5 g·kg−1 in the 0–30 cm soil layer. The daily mean air temperature and accumulated precipitation during the cotton growth period (April to October) in the two years of the trial were shown in Figure 1.

2.2. Experimental Design and Management

The field experiment was conducted in a randomized block design with three replicated groups. The source–sink processing method refers to Luo et al. [31] with some improvements. Including a no cutting source and sink treatment (CK), cutting 1/2 leaves per plant (1/2L) and cutting 1/2 bolls per plant (1/2B), which were applied at the initial flowering stage (IFS), flowering and boll stage (FABS) and full boll stage (FBS), respectively. Treatments were applied to all plots throughout the season. The specific time of treatment are listed in Table 1. The phenotypes were shown in Figure 2.
The cotton cultivar ‘Xinluzao 78’ (Xinjiang Jinfengyuan Seed Industry Co., Ltd., Wensu, China) was selected in this study. Cotton was cultivated using the wide-narrow row planting method commonly practiced in Xinjiang, with row spacing of 66 + 10 cm, and plant spacing of 10 cm. The theoretical seeding density was 26.3 × 104 plants ha−1. The sowing dates were 22 April 2023 and 21 April 2024. The total irrigation volumes were 3420 and 4050 m3·ha−1 in 2023 and 2024, respectively. Fertilizers were applied with water from June to August, with Urea (46% N) and potassium dihydrogen phosphate (52% P2O5, 34% K2O) each applied at 487.5 kg·ha−1 in 2023 and 532.5 kg·ha−1 in 2024. Pest, disease, and weed control measures followed standard field practices.

2.3. Sampling and Measurements

N content, SPAD, photosynthetic rate, leaf area index and dry matter accumulation were measured or sampled at 82 (initial flowering stage), 94 (full flowering stage), 104 (flowering and boll stage), 120 (full boll stage), 129 (later full boll stage) days after sowing in 2023 and 80 (initial flowering stage), 95 (full flowering stage), 106 (flowering and boll stage), 118 (full boll stage), 126 (later full boll stage) days after sowing in 2024.

2.3.1. Canopy Temperature and Humidity of Cotton

To accurately monitor the temperature and humidity within the cotton canopy and investigate the relationship between canopy temperature and humidity and cotton yield. A high-precision automatic temperature and humidity probe (RC-4HC, Jiangsu Jingchuang Electrical Co., Ltd., Nanjing, China) with precisions of 0.5 °C and 3% relative humidity, respectively, was installed before the sink-source treatment. Mainly through purchasing on the enterprise’s official website (www.e-elitech.com). To prevent damage to the instrument on rainy days while ensuring adequate ventilation for accurate sensing of external humidity and temperature changes, it was placed under an instrument shelter. The probe was installed in the center of the wide cotton rows and maintained a height of 30 cm above the ground. Temperature and humidity of the cotton canopy were recorded every 30 min [32]. Once the experiment was completed, the data were exported using the Jingchuang Data Center software (7.2.6).

2.3.2. Leaf Area Index (LAI) and Mean Leaf Inclination Angle (MTA)

The cotton canopy was divided into top, middle, and bottom parts. Due to the low number of leaves in the bottom canopy and their limited light exposure [17,33], data from the bottom canopy were excluded from subsequent analyses and discussions. The leaf area index (LAI) and mean inclination angle (MTA) of the leaves was measured using an LAI-2000 canopy analyzer (LI-Cor, Lincoln, NE, USA) at top (1/3) and middle (2/3) of the canopy in the late afternoon.

2.3.3. Photosynthetic Rate (Pn) and Relative Chlorophyll Content (SPAD)

On each sampling date, the net photosynthetic rate (Pn) and stomatal conductance (Gs) of the second-youngest main stem leaves were measured between 11:00 and 13:00 using a LI-6400 XT portable photosynthesis system (LI-COR, Lincoln, NE, USA). Environmental settings in leaf chamber included light intensity = 1800 μmol m−2 s−1, reference [CO2] = 400 μmol mol−1, relative humidity 60 ± 10%, and flow rate = 500 μmol s−1. The measured leaves were marked for subsequent measurements. In order to avoid the instantaneous interference caused by the photosynthetic “midday rest” phenomenon at noon due to strong light and high temperatures on the optical properties of leaves. On the same day, these marked leaves were measured by SPAD-502 plus chlorophyll analyzer from 18:00 to 19:00.

2.3.4. Dry Matter Accumulation, N Content and Yield

On the sampling date, five plants were randomly selected from each treatment and brought to the laboratory for decomposition. These samples were primarily divided into stems (flow), leaves (source), squares, flowers, and bolls (sink), which were placed in paper bags, then they dried at a controlled temperature of 105 °C for 30 min and then at 80 °C for 48 h to obtain a constant weight for the subsequent biomass determinations. Next, the stem, leaves, and sink were pulverized and total nitrogen was determined by Kjeldahl method.
Seed cotton was hand harvested on 1 October 2023 and 2 October 2024. Specifically, before harvest, a representative sample of 10 cotton plants was selected from each plot, the number of bolls per plant was recorded, and the boll opening of the 10 plants were weighed to calculate the average boll weight. A sub-sampling area of about 6.67 m2 (2.3 m wide × 2.9 m long) was designated in the plot, after which all the flocculated bolls in the area were harvested (if there were any sampling plants in the area, their yields would be incorporated) to calculate the seed cotton yield per unit area.

2.4. Statistical Analysis

The analysis of variance (ANOVA) and Duncan’s multiple range test were performed using SPSS 25.0 software (SPSS Inc., Chicago, IL, USA). All others figures and tables in the manuscript were drawn using Origin 2022b (Originlab, Northampton, MA, USA) and Microsoft Office 2016. The data in the figures and tables are the mean ± SD of three replicates. In order to reflect the differences between different treatments more clearly, we plotted the percentage change in SPAD, Pn and Gs, i.e., (Treatment-CK)/CK. The radar map was drawn by min-max normalization method.

3. Results

3.1. Cotton Yield and Its Components

Source–sink treatment showed significant difference on yield and its constituent factors, except for lint percentage. The boll weight and yield were all affected by treatment period and source–sink treatment. However, there was no significant difference in boll number and boll weight between the CK treatment and the 1/2L treatment. Compared with CK, under the 1/2B treatment, the number of bolls per plant was significantly reduced by 26.4–32.7%, 33.0–36.7%, and 37.4–52.0% at IFS, FABS and FBS, respectively, and the boll weight was significantly increased by 8.8–10.5% under 1/2B treatment at IFS. Eventually, the seed cotton yield was significantly decreased by 17.7–23.3%, 26.2–31.3% and 35.7–41.8% under 1/2B treatment at IFS, FABS, and FBS, respectively (Table 2). Compensation ratios for seed cotton yield under the 1/2B treatment were quantified as 26.7–32.3%, 18.7–23.8%, and 8.1–14.3% for IFS, FABS, and FBS, respectively. Contrastingly, the 1/2L treatment (The loss rate was lower than 6%) maintained yield parity with CK, showing no statistically significant differences (Figure 3).

3.2. Canopy Temperature and Humidity

The canopy average and maximal temperature in the leaf reduction treatment was significantly higher than that in the sink removal treatment, while the canopy humidity exhibited an opposite trend (Figure 4). Throughout the full boll stage to late full boll stage, the average temperature measured under the FABS-1/2L and FBS-1/2L treatment was 0.6–9.0% and 7.6–11.3% higher than IFS-1/2L treatment, with the same pattern observed for maximum canopy temperature. The sink removal treatment mainly manifested as IFS-1/2B < FABS-1/2B < FBS-1/2B (Figure 4A,B).
The earlier the source–sink treatment time, the higher the canopy humidity value. Specifically, during the full boll stage to late full boll stage, in the leaf reduction treatment, the average canopy humidity of the FBS-1/2L treatment decreased by 10.0–17.0% and 0.3–7.0%, compared to IFS-1/2L and FABS-1/2L, respectively. For boll reduction processing, IFS-1/2B increased by 0.7–3.9% and 8.9–20.0%, compared to FABS-1/2B and FBS-1/2B, respectively (Figure 4C,D).

3.3. Leaf Area Indices and Mean Leaf Inclination Angle

Throughout the cotton growth duration, the LAI of upper and middle canopies showed a parabolic variation, initially rising and then falling. The impact of different treatments on LAI varied significantly. In addition, the earlier the leaf reduction (1/2L) and sink removal (1/2B) treatment was conducted, the higher the LAI. Specifically, during the full boll stage to later full boll stage, compared with FABS-1/2L and FBS-1/2L treatments, IFS-1/2L treatment led to an increase in both upper and middle LAI. The upper LAI was elevated by 2.1–30.1% and 22.4–73.2%, whereas the middle LAI was enhanced by 0.7–2.7% and 1.9–10.4%, respectively. Under sink reduction treatments, the IFS-1/2B treatment exhibited pronounced advantages. Its upper canopy LAI surpassed that of the FABS-1/2B and FBS-1/2B treatment by 4.7–52.8% and 10.1–69.7%, respectively, while the middle canopy LAI increased by 1.8–9.1% and 17.3–22.9%, respectively (Figure 5A–D).
The study indicates that the MIA in the 1/2L and CK treatment was markedly smaller compared to that in the 1/2B treatment during the same growth stage. From the full boll stage to the late full boll stage, earlier leaf removal resulted in higher MIA of top canopy, while the MIA of middle canopy showed the opposite trend. Specifically, in the FBS-1/2L treatment, the MIA of the top canopy was elevated by 10.1–65.2% and 5.7–22.8%, compared to the IFS-1/2L and FABS-1/2L treatments, respectively. Conversely, the MIA of the middle canopy experienced a reduction of 6.7–20.2% and 6.7–18.2% in the FBS-1/2L treatment relative to the IFS-1/2L and FABS-1/2L treatments. In the boll removal treatment, the MIA of different treatment groups followed the order: FBS-1/2B > FABS-1/2B > IFS-1/2B, and this pattern was consistent in both the upper and middle canopies (Figure 5E–H).

3.4. Percentage Change in SPAD and Photosynthesis of Leaf

Source–sink treatment had a significant effect on SPAD values in both years of the current study, with 1/2B > CK > 1/2L at the same treatment period. In addition, earlier treatment timing was associated with higher SPAD values in 1/2B treatments, whereas a converse trend was observed in 1/2L treatments. Under the full boll stage to later full boll stage, compared to CK, the SPAD in IFS-1/2L, FABS-1/2L and FBS-1/2L treatments decreased by 6.0–8.2%, 4.4–5.5%, and 1.7–3.7%, respectively. Conversely, SPAD in IFS-1/2B, FABS-1/2B, and FBS-1/2B treatments increased by 3.0–7.5%, 1.0–4.2%, and 0.1–2.3%, respectively (Figure 6A,B).
Initially, the 1/2L treatment boosted the Pn, yet Pn decreased progressively as the treatment duration increased. In contrast, the 1/2B treatment led to a reduction in Pn in the early stages. However, as the reproductive process advanced and the leaves gradually senesced, the Pn of the 1/2B treatment eventually surpassed that of the CK. Under the full boll stage to later full boll stage, compared to CK, the Pn in IFS-1/2L, FABS-1/2L and FBS-1/2L treatments increased by −19.0–4.1%, −9.6–17.5%, and 7.2–32.7%, respectively. The Pn in IFS-1/2B, FABS-1/2B, and FBS-1/2B treatments increased by −10.1–5.0%, −7.6–29.5%, and −7.1–9.1%, respectively. The regulation of Gs was similar to the law of Pn (Figure 7A–D).

3.5. Cotton Biomass Accumulation and Allocation

As growth advanced, the dry matter accumulation in source (leaf) and flow (stem) organs initially increased and then decreased with the sink organs biomass showing a gradual increasing trend, and the distribution proportion of biomass in the sink (squares, flowers, and bolls) increasing gradually (Figure 8a,b). During the full boll stage to the late full boll stage, the measured flow organ (stem) biomass was increased by 11.0–34.3% and 8.6–16.5% in the FBS-1/2L treatment, compared to IFS-1/2L and FABS-1/2L, respectively, under the reduced-source treatments. Compared to IFS-1/2L and FABS-1/2L, the dry matter mass of FBS-1/2L sink organs (boll) increased by 5.0–18.0% and 0.8–13.5%, respectively. But, the dry matter mass of FBS-1/2L source organs (leaf) decreased by 20.2–27.2% and 0.9–19.3%. For the boll removal treatment, during the full boll stage to the late full boll stage, compared to FABS-1/2B and FBS-1/2B, the source organs in the IFS-1/2B treatment increased by 0.7–15.6% and 7.0–27.3%, respectively. The flow organs in IFS-1/2B increased by 3.9–6.1% and 5.0–11.8%, respectively. The sink organs in IFS-1/2B increased by 1.7–12.1% and 13.6–55.8%, respectively (Figure 8a, (A–N)).
In addition, the dry matter allocation of the source and flow organs decreased and that of the boll organs increased the later the treatment time during the full boll stage to the late full boll stage under the leaf reduction treatments. Compared with IFS-1/2L, the source organ dry matter allocation decreased by 4.9–28.7% and 24.0–36.1% in FABS-1/2L and FBS-1/2L treatments, respectively, and increased by 0.7–3.7% and 2.4–5.8% in the boll organ dry matter allocation, respectively. For the reduced boll treatments, FBS-1/2B boll organs had the lowest dry matter allocation (Figure 8b, (A–N)).

3.6. N Content in Organs of Cotton

The N content in organs of cotton differed significantly between the source–sink treatment and was affected by treatment time. In 1/2L treatment, the later the treatment time, the higher the N content of each organ (stem, leaf, and sink) in cotton, i.e., IFS-1/2L < FABS-1/2L < FBS-1/2L, and 1/2L treatment was less than CK. The 1/2B treatment was the opposite of this. During the period from the full boll stage to the late full boll stage, the FBS-1/2L and FABS-1/2L treatment than IFS-1/2L treatment, the stem N content was increased by 3.0–6.7% and 8.2–11.1%, respectively. The leaf N content was increased by 2.3–6.3% and 3.1–11.4%, respectively. The sink N content was increased by 3.1–9.5% and 10.8–15.2%, respectively. The FBS-1/2B and FABS-1/2B treatment than IFS-1/2B treatment, the stem N content was decreased by 3.1–6.8% and 13.1–18.6%, respectively. The leaf N content was decreased by 1.1–2.7% and 6.1–11.4%, respectively. The sink N content was decreased by 3.0–8.4% and 12.4–23.9%, respectively (Figure 9A–D).

3.7. Individual Effect on Sink Dry Weight

In 1/2L treatment, a strong positive correlation between N content, SPAD, and sink dry weight was observed during full boll stage in this study (Figure 10A). Moreover, during the full boll stage and later full boll stage, the sink dry weight was positively correlated with Pn and the top-canopy MTA was positively correlated with Pn (Figure 10B–C). In 1/2B treatment, the N content and sink dry weight were fitted separately according to the measurement period at the full boll and late full boll of cotton growth. N content was significantly correlated with the sink dry weight, but the increase in sink dry weight at the full boll stage contributed significantly more to N content than at the late full boll stage (Figure 10D). Thus, the variation in N content of leaf caused by source–sink regulation is of importance for determining the sink dry weight.

3.8. The Relationship Between the Various Factors

Figure 11 shows pairwise correlations between various factors and yield for cotton sampled on full boll stage and late full boll stage during the 2023 and 2024 growing seasons. In 1/2L treatment, The T-MIA, N content (leaf and stem), SPAD and sink dry weight exhibited a positive correlation with the yield. The significant associations were between leaf-N content, SPAD and Pn (Figure 11A). Figure 10 also shows that the Pn was significantly correlated with the dry matter weight of the sink under a single period of time. In 1/2B treatment, the MCH, M-LAI, N content (steam, leaf, and sink), SPAD and sink dry weight exhibited a positive correlation with the yield. But the T-MIA was negatively correlated with the yield. In addition, strong associations were observed between N content and sink dry weight (Figure 11B). Thus, the results indicate that variability in yield induced by source–sink regulation was predominately associated with the N content of leaf.
In addition, radar plots showed that N content of leaf, Pn, and boll weight were all FBS > FABS > IFS in the 1/2L treatment, but the pattern was reversed in the 1/2B treatment for N content of leaf and boll weight, and Pn was largest in FABS, further indicating the importance of the boll size for yield formation (Figure 11C,D).

4. Discussion

Achieving high crop yields is contingent upon the coordinated relationship between source and sink organs [21]. However, source–sink imbalances are prevalent under field production conditions. Previous research has established that optimizing canopy architecture significantly impacts light energy utilization, a combination of erect leaves in the upper canopy and horizontal leaves in the middle-to-lower canopy can markedly enhance population photosynthetic efficiency [17,34,35]. Maize breeding studies demonstrate that an erectophile leaf orientation coupled with a high leaf area index enhances light interception by up to 14%, facilitating yield breakthroughs [35,36,37]. In this study, although the 1/2B treatment theoretically optimized the canopy structure, as evidenced by an MTA in the upper canopy, a decreased MTA in the middle canopy, and a high LAI, no significant correlation was observed between the photosynthetic rate and yield. (Figure 5 and Figure 11B). Ultimately, the reduction in boll number resulted in a significant decrease in yield (Table 2). This suggests that even with optimized canopy architecture, the regulation of sink capacity remains the critical determinant for achieving high cotton yields.
Conventionally, sink capacity has been characterized based on quantitative (e.g., boll number per plant) and qualitative (e.g., single boll weight) traits of reproductive organs, including buds, flowers, and bolls [38,39]. Our findings reveal that de-bolling treatments implemented at various developmental stages consistently led to a significant reduction in the number of bolls per plant (Table 2).
Crop plants can initiate compensatory effects in response to leaf damage [40], and the optimization of photosynthetic performance is crucial for cotton dry matter accumulation and yield formation [41]. In the present study, while yields from 1/2L treatments were lower than those of the CK, the difference was not statistically significant (Table 2). This outcome can be attributed to several factors: (1) The 1/2L treatment altered the sink-source ratio, inducing premature plant senescence [42], the severity of which intensified when treatments were applied earlier in the growing season [36]. Concurrently, a significant reduction in the leaf area index diminished the canopy’s light interception capacity [18], ultimately contributing to lower yields [43]. (2) Following 1/2L treatment, the net photosynthetic rate (Pn) was transiently significantly higher than that of the CK (Figure 7A,B), indicating that plants utilized photosynthetic compensation mechanisms to enhance assimilate synthesis, thereby mitigating biomass loss. Notably, the extent of yield loss varied depending on the developmental stage at which 1/2L occurred, with the following order observed: FBS-1/2L < FABS-1/2L < IBS-1/2L (Table 2 and Figure 3). Specifically, the SPAD values of leaves at the FBS-1/2L treatment were the highest (Figure 6A,B), and the N content was also the highest (Figure 9A–D and Figure 11C). Moreover, both SPAD values and N content were significantly positively correlated with Pn, and Pn was further significantly correlated with the dry matter weight of storage organs (Figure 11A). This observed pattern shares similarities with the photosynthesis-source–sink regulatory mechanisms reported in rice [44], suggesting the potential existence of a conserved physiological regulatory pathway governing photosynthetic compensation across crop species.
The yield compensation effect induced by boll shedding has significant period differences in cotton production [30,45]. The present study showed that the number of bolls set per plant, boll weight, seed cotton yield, and compensation rate showed the pattern of IFS-1/2B > FABS-1/2B > FBS-1/2B under 1/2B treatment (Table 2), confirming that the time of sink organ removal was positively correlated with yield loss. Among them, the FBS-1/2B treatment resulted in the lowest yield due to the insufficient time for the reconstruction of the source–sink relationship and the limitation of the compensation effect [46], which provided a theoretical basis for the source–library synergistic regulation in the high-yield cultivation of cotton. Therefore, through the dynamic optimization of source–sink relationship between the IFS and FABS, a population structure conducive to boll development can be constructed, which in turn enhances the yield potential [47]. Correlation analysis and radar pattern analysis showed that leaf N content was significantly and positively correlated with yield, and its dynamics was consistent with treatment time (IFS-1/2B > FABS-1/2B > FBS-1/2B) (Figure 11B,D). Based on these findings, it is advised that rigorous water and fertilizer management be applied during the bud and boll shedding phases. This can bolster plant compensation mechanisms by boosting leaf N metabolism efficiency, thereby sustaining the development of sink organs.
Although this study was conducted in Xinjiang, China’s main cotton-growing region, its results are limited in terms of representativeness due to the fact that it was carried out at a single location. Considering the differences in climate conditions and variety distribution between southern and northern Xinjiang, future studies should be conducted at multiple locations and using different varieties for further validation. Additionally, while the current work primarily focuses on physiological analysis, future research could be expanded to include molecular mechanisms to provide a more comprehensive and in-depth understanding of the underlying mechanisms.

5. Conclusions

The boll removal treatment optimized the canopy light transmission structure (increased the MIA of the top canopy and LAI of the middle canopy). However, the number of bolls set per plant was 37.4–52.0% lower than that of the CK, which directly led to yield limitation. Thus, the core regulator of high-yield cotton fields was sink strength. In addition, the 1/2L treatments achieved yield parity with the CK by inducing photosynthetic compensation mechanisms. Where the 1/2B treatments, yield hinged on leaf N, giving compensation rates of 26–32 % (IFS-1/2B), 19–24 % (FABS-1/2B) and 8–14 % (FBS-1/2B). Based on this, a precise control strategy was proposed: optimizing the sink quality through moderate boll thinning at the IFS, enhancing water and fertilizer supply at the FABS and strengthening sink organ protection at the FBS to balance the source–sink relationship, so as to achieve a synergistic enhancement of the yield components.

Author Contributions

Conceptualization and supervision, K.Y., M.D. and Z.L.; methodology, M.D., F.L. and X.T.; validation, Z.Z. and Q.L.; formal analysis, Z.Z. and J.Z.; writing—original draft preparation and visualization, Z.Z.; data curation, Z.Z., K.L., Z.S. and X.J.; investigation, K.L., Q.L., Z.S., J.Z., X.J., and M.Y.; project administration, M.Y.; writing—review and editing, G.C., S.W., S.L., F.L., X.T., Z.L. and M.D.; resources, G.C., S.W. and S.L.; funding acquisition, M.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science and Technology Planning Projects of the Xinjiang Production and Construction Corps, grant number 2024AB030 and 2024ZD097, and the Tianshan Talent Training Program, grant number 2023TSYCTD004.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

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

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Precipitation (blue bar), daily maximum temperature (red line), and daily minimum temperature (black line) during cotton growth period in 2023 (A) and 2024 (B).
Figure 1. Precipitation (blue bar), daily maximum temperature (red line), and daily minimum temperature (black line) during cotton growth period in 2023 (A) and 2024 (B).
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Figure 2. Phenotype of cotton plants after different treatments in the sub-plot area. Characteristics in source–sink relationship are specifically indicated in the boxes. 1/2L represent the cutting 1/2 leaves per plant, CK represent the no cutting source and sink treatment, 1/2B represent the cutting 1/2 bolls per plant.
Figure 2. Phenotype of cotton plants after different treatments in the sub-plot area. Characteristics in source–sink relationship are specifically indicated in the boxes. 1/2L represent the cutting 1/2 leaves per plant, CK represent the no cutting source and sink treatment, 1/2B represent the cutting 1/2 bolls per plant.
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Figure 3. The percentage of yield loss (A,B) and compensation rate (C,D) of cotton under different source–sink treatments in 2023 and 2024. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively.
Figure 3. The percentage of yield loss (A,B) and compensation rate (C,D) of cotton under different source–sink treatments in 2023 and 2024. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively.
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Figure 4. Effects of the source–sink treatments on the cotton canopy temperature (A,B) and humidity (C,D) in the 2023 and 2024 growing seasons. The black column diagram, red column diagram, and line diagram represent the minimum temperature, maximum temperature, and average temperature of the canopy, respectively. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. Different lowercase letters indicate significant difference for a parameter between treatments at p < 0.05.
Figure 4. Effects of the source–sink treatments on the cotton canopy temperature (A,B) and humidity (C,D) in the 2023 and 2024 growing seasons. The black column diagram, red column diagram, and line diagram represent the minimum temperature, maximum temperature, and average temperature of the canopy, respectively. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. Different lowercase letters indicate significant difference for a parameter between treatments at p < 0.05.
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Figure 5. Dynamic change in LAI of top and middle canopy (A–D), MIA of top and middle canopy (E–H) for cotton grown under source–sink treatments during the 2023 and 2024 growing seasons. The IFS, FABS, and FBS are represented by initial flowering stage, flowering and boll stage, and full boll stage, respectively. The green dotted lines in the figure represent the processing times of the three source–sink, respectively.
Figure 5. Dynamic change in LAI of top and middle canopy (A–D), MIA of top and middle canopy (E–H) for cotton grown under source–sink treatments during the 2023 and 2024 growing seasons. The IFS, FABS, and FBS are represented by initial flowering stage, flowering and boll stage, and full boll stage, respectively. The green dotted lines in the figure represent the processing times of the three source–sink, respectively.
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Figure 6. Percentage change in SPAD (A,B) for cotton grown under six source–sink treatments (IFS-1/2L, IFS-1/2B, FABS-1/2L, FABS-1/2B, FBS-1/2L, FBS-1/2B) during the 2023 and 2024 growing seasons compared with CK. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. The green dotted lines in the figure represent the processing times of the three source–sink, respectively.
Figure 6. Percentage change in SPAD (A,B) for cotton grown under six source–sink treatments (IFS-1/2L, IFS-1/2B, FABS-1/2L, FABS-1/2B, FBS-1/2L, FBS-1/2B) during the 2023 and 2024 growing seasons compared with CK. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. The green dotted lines in the figure represent the processing times of the three source–sink, respectively.
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Figure 7. Percentage change in photosynthesis (A–D) for cotton grown under six source–sink treatments (IFS-1/2L, IFS-1/2B, FABS-1/2L, FABS-1/2B, FBS-1/2L, FBS-1/2B) during the 2023 and 2024 growing seasons compared with CK. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. The green dotted lines in the figure represent the processing times of the three source–sink, respectively.
Figure 7. Percentage change in photosynthesis (A–D) for cotton grown under six source–sink treatments (IFS-1/2L, IFS-1/2B, FABS-1/2L, FABS-1/2B, FBS-1/2L, FBS-1/2B) during the 2023 and 2024 growing seasons compared with CK. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. The green dotted lines in the figure represent the processing times of the three source–sink, respectively.
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Figure 8. Effects of the source–sink treatments on biomass accumulation (a) and allocation (b) of cotton in the 2023 and 2024 growth seasons. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively.
Figure 8. Effects of the source–sink treatments on biomass accumulation (a) and allocation (b) of cotton in the 2023 and 2024 growth seasons. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively.
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Figure 9. N content in organs of cotton at full boll stage (A,C) and later full boll stage(B,D) under different source–sink treatments in 2023 and 2024. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. Different lowercase letters indicate significant difference for a parameter between treatments within the same year at p < 0.05.
Figure 9. N content in organs of cotton at full boll stage (A,C) and later full boll stage(B,D) under different source–sink treatments in 2023 and 2024. The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. Different lowercase letters indicate significant difference for a parameter between treatments within the same year at p < 0.05.
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Figure 10. Correlation between sink dry weight, SPAD and N content under 1/2L treatment at FBS (A). Correlation between sink dry weight, SPAD and N content under 1/2L treatment at FBS and LFBS (B). Correlation between MIA of top canopy and Pn under 1/2L treatment at FBS and LFBS (C). Correlation between sink dry weight and N content under 1/2B treatment at FBS and LFBS (D).
Figure 10. Correlation between sink dry weight, SPAD and N content under 1/2L treatment at FBS (A). Correlation between sink dry weight, SPAD and N content under 1/2L treatment at FBS and LFBS (B). Correlation between MIA of top canopy and Pn under 1/2L treatment at FBS and LFBS (C). Correlation between sink dry weight and N content under 1/2B treatment at FBS and LFBS (D).
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Figure 11. Heat map showing the correlation analysis between the various factors. The correlation of each factor under 1/2L treatment (A); The correlation of each factor under 1/2B treatment (B); Asterisks (*) indicate the level of significance: * p < 0.05, ** p < 0.01. Radar plots indicating dry matter weight of the sink, N content of leaves and Pn changes under 1/2L (C) and 1/2B (D) treatments during full boll stage and later full boll stage. The initial flowering stage, flowering and boll stage and full boll stage are represented in the figure as IFS, FABS, and FBS, respectively.
Figure 11. Heat map showing the correlation analysis between the various factors. The correlation of each factor under 1/2L treatment (A); The correlation of each factor under 1/2B treatment (B); Asterisks (*) indicate the level of significance: * p < 0.05, ** p < 0.01. Radar plots indicating dry matter weight of the sink, N content of leaves and Pn changes under 1/2L (C) and 1/2B (D) treatments during full boll stage and later full boll stage. The initial flowering stage, flowering and boll stage and full boll stage are represented in the figure as IFS, FABS, and FBS, respectively.
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Table 1. The timing of the specific treatment periods and each treatment during the 2023 and 2024 growing season.
Table 1. The timing of the specific treatment periods and each treatment during the 2023 and 2024 growing season.
YearPeriodTimeTreatment
2023IFS6 JulyCK
1/2L
1/2B
FABS28 JulyCK
1/2L
1/2B
FBS15 AugustCK
1/2L
1/2B
2024IFS6 JulyCK
1/2L
1/2B
FABS28 JulyCK
1/2L
1/2B
FBS13 AugustCK
1/2L
1/2B
The IFS, FABS, and FBS are represented by initial flowering stage, flowering and boll stage, and full boll stage, respectively.
Table 2. Effects of different source–sink treatments on seed cotton yield and yield components from 2023 to 2024 in Shihezi, China.
Table 2. Effects of different source–sink treatments on seed cotton yield and yield components from 2023 to 2024 in Shihezi, China.
Year (Y)Period (P)Treatment (T)Boll Number (Bolls·Plant−1)Boll Weight (g)Lint Percentage (%)Seed Cotton Yield (kg·hm−2)
2023 CK9.1 ± 1.2 a5.7 ± 0.1 bc45.7 ± 0.5 a5875.5 ± 292.7 a
IFS1/2L7.7 ± 1.1 ab5.7 ± 0.3 bc45.5 ± 0.5 a5547.0 ± 70.0 a
1/2B6.7 ± 0.8 b6.3 ± 0.1 a44.8 ± 0.3 a4836.0 ± 153.1 b
FABS1/2L9.2 ± 0.3 a5.4 ± 0.2 c46.3 ± 0.5 a5618.5 ± 179.5 a
1/2B6.1 ± 0.3 b6.1 ± 0.1 ab43.9 ± 0.7 a4339.0 ± 134.1 b
FBS1/2L9.2 ± 1.5a5.5 ± 0.3 c45.8 ± 0.5 a5742.0 ± 409.6 a
1/2B5.7 ± 1.1b5.8 ± 0.2 bc44.1 ± 0.7 a3779.5 ± 353.8 c
2024 CK9.8 ± 0.4 a5.7 ± 0.1 bc44.4 ± 0.6 a5947.2 ± 91.7 a
IFS1/2L8.4 ± 0.3 b5.5 ± 0.1 cd43.7 ± 0.4 a5594.1 ± 466.0 a
1/2B6.6 ± 0.9 c6.2 ± 0.1 a43.8 ± 0.1 a4563.2 ± 144.2 b
FABS1/2L8.6 ± 0.9 ab5.3 ± 0.1 d45.1 ± 0.3 a5645.6 ± 124.0 a
1/2B6.2 ± 0.4 c5.9 ± 0.1 ab42.7 ± 1.0 a4087.6 ± 135.4 b
FBS1/2L9.5 ± 0.9 ab5.5 ± 0.1 cd44.8 ± 0.2 a5775.4 ± 306.8 a
1/2B4.7 ± 0.1 d5.7 ± 0.3 bc43.4 ± 1.4 a3457.5 ± 185.2 c
Source of variance
Ynsnsnsns
Pns*ns**
T****ns**
Y × Pnsnsnsns
Y × Tnsnsnsns
P × Tns*ns**
Y × P × Tnsnsnsns
The IFS, FABS, and FBS are represented initial flowering stage, flowering and boll stage and full boll stage, respectively. Different lowercase letters indicate significant difference for a parameter between treatments within the same year at p < 0.05. The ns indicates that results are not significant, whereas an asterisk (*) and (**) denote a significant difference.
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MDPI and ACS Style

Zhang, Z.; Li, K.; Liao, Q.; Shi, Z.; Yu, K.; Zhu, J.; Jia, X.; Chen, G.; Wan, S.; Lou, S.; et al. Sink Strength Governs Yield Ceiling in High-Yield Cotton: Compensation Effects of Source–Sink Damage and Reproductive Stage Regulation. Agronomy 2025, 15, 2099. https://doi.org/10.3390/agronomy15092099

AMA Style

Zhang Z, Li K, Liao Q, Shi Z, Yu K, Zhu J, Jia X, Chen G, Wan S, Lou S, et al. Sink Strength Governs Yield Ceiling in High-Yield Cotton: Compensation Effects of Source–Sink Damage and Reproductive Stage Regulation. Agronomy. 2025; 15(9):2099. https://doi.org/10.3390/agronomy15092099

Chicago/Turabian Style

Zhang, Zhenwang, Kexin Li, Qinghua Liao, Zhijie Shi, Keke Yu, Junqi Zhu, Xiyu Jia, Guodong Chen, Sumei Wan, Shanwei Lou, and et al. 2025. "Sink Strength Governs Yield Ceiling in High-Yield Cotton: Compensation Effects of Source–Sink Damage and Reproductive Stage Regulation" Agronomy 15, no. 9: 2099. https://doi.org/10.3390/agronomy15092099

APA Style

Zhang, Z., Li, K., Liao, Q., Shi, Z., Yu, K., Zhu, J., Jia, X., Chen, G., Wan, S., Lou, S., Yang, M., Li, F., Tian, X., Li, Z., & Du, M. (2025). Sink Strength Governs Yield Ceiling in High-Yield Cotton: Compensation Effects of Source–Sink Damage and Reproductive Stage Regulation. Agronomy, 15(9), 2099. https://doi.org/10.3390/agronomy15092099

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