Melatonin Affects Leymus chinensis Aboveground Growth and Photosynthesis by Regulating Rhizome Growth

: Leymus chinensis is a perennial rhizomatous clone plant. It exhibits strong rhizomatous tillering and clonal growth through asexual reproduction. The root system is interdependent with aboveground growth and root growth can regulate aboveground growth and photosynthesis. Melatonin has been shown to regulate root growth and promote photosynthesis. However, it remains unclear whether melatonin affects aboveground growth and photosynthesis by regulating rhizome growth. To address this gap, we studied nine Leymus chinensis from different geographical locations, all grown under the same conditions. We selected two materials with strong (LC19) and weak (LC2) rhizome growth abilities from nine materials and treated them with exogenous melatonin. We found there were significant positive correlations between stem length, plant height, leaf number and rhizome traits. Additionally, rhizome traits showed significant positive correlations with photosynthetic indices and chlorophyll content. Specifically, for LC2, treatment with 200 µ mol/L melatonin significantly increased root length, the number of extravaginal ramets and rhizome clonal growth rate by 88.72%, 43.75% and 43.70%, respectively, resulting in significant increases in aboveground traits. Similarly, for LC19, 200 µ mol/L melatonin treatment led to significant increases of 74.66%, 23.02%, 62.71% and 62.72% in four traits, respectively, along with aboveground trait improvements. Furthermore, around 300 µ mol/L melatonin treatment promoted photosynthetic efficiency in LC2, while around 100 µ mol/L melatonin treatment had the same effect in LC19. In conclusion, our study highlights the relationship between rhizome growth ability, aboveground growth and photosynthesis in Leymus chinensis . Additionally, it suggests that exogenous melatonin can enhance aboveground growth and photosynthesis by regulating rhizome growth.


Introduction
Leymus chinensis (Trin.)Tzvelev is a perennial rhizomatous plant belonging to the genus Leymus in the grass family [1].It is a dominant species in the eastern Eurasian steppe, mainly distributed in the northeast plain of China, the eastern part of the Inner Mongolia Plateau, the area around Lake Baikal in Russia, Mongolia and North Korea [2].Leymus chinensis has excellent nutritional value, good palatability and strong cold, drought, salt, alkali and grazing resistance [3].As high-quality forage, the protein content of Leymus chinensis can reach 12% in fresh grass, and the crude protein content can still be maintained at about 10% after making hay [4,5].In China, the annual output of Leymus chinensis has reached 1.31 × 106 tons, and it occupies more than 90% of the market share together with alfalfa, silage corn and other forages [6].The rhizomes of Leymus chinensis can store and transport nutrients, transmit signals, adapt to adversity, etc.It can maintain its nutritional reproduction by constantly producing new rhizomes and clonal branches, thereby expanding the population size and becoming the dominant species in some grassland communities [7,8].At the same time, the rhizomes of Leymus chinensis help it achieve perennial growth, increase biomass and improve resistance to abiotic stress [9].
The growth of root systems directly affects the growth, nutrition and yield of the aboveground portion of plants [10,11].In general, the more developed the root system and the stronger its vitality, the better the aboveground part grows.The root system absorbs water, inorganic minerals and organic matter from the soil for the growth and utilization of the aboveground part, while the aboveground part synthesizes organic matter through photosynthesis to supply sugars and vitamins for root growth [12].The root system helps the leaves to continue to grow and maintain vitality.The control of the root system is expected to control the growth and vitality of the leaves, prolong the life of the leaves and enhance the photosynthesis of the leaves [13].For example, low doses of La (III) can induce the endocytosis mechanism, leading to a sudden increase in the nutrient content of root cells, thus promoting photomorphogenesis in seedlings, plant photosynthesis and growth [14].Root-zone freezing of alfalfa increased stomatal conductance (Gs) to improve plant photosynthesis to enhance carbon dioxide supply, thereby promoting photosynthetic electron transport activity and phosphorylation, thereby increasing the photochemical efficiency level of photosystem II (PSII).Vigorous root growth ensures the stable protein and chlorophyll content of leaves and leaves are active [12].The root system has strong vitality and slow aging, which can ensure the long-term transport of substances required for the growth of aboveground organs and promote the accumulation of various physiological metabolic activities and light-contract substances in leaves [15].
Plant growth regulators can regulate plant root growth, improve photosynthetic efficiency, delay leaf senescence and alleviate abiotic stress damage [16].Melatonin can not only effectively regulate the development of plant roots and leaves [17,18], but also affect photosynthetic efficiency and photosynthetic pigment content.For example, under drought stress, melatonin promoted the root system and vitality of cucumber (Cucumis sativus) and increased the root to shoot ratio [19].Melatonin can protect plants from heavy metal stress, and it can help plants inhibit the ability of heavy metal transport from roots to buds, thereby reducing heavy metal accumulation [20].In pricklyash (Zanthoxylum), a 400 µmol/L melatonin treatment enhanced chlorophyll fluorescence parameters, chlorophyll and carotenoid contents and electron transport and photosynthetic efficiency in PSII of seedlings under waterlogging stress [21].In wheat, exogenous melatonin treatment regulated photosynthetic gas exchange, up-regulated the genes of chlorophyll protein complex protein encoding light harvesting in photosynthesis and genes related to chlorophyll and carotenoid biosynthesis [22].In maize, exogenous melatonin treatment significantly improved photosynthetic carbon fixation and photosynthesis under drought stress [13].In kiwifruit, 100 µmol/L melatonin treatment promoted root growth and reduced pigment degradation.It inhibited stomata closure, enhanced light energy absorption, promoted electron migration in PSII and up-regulated the expression of 11 transcriptional genes of CO2-fixing enzymes (Rubisco, PGK, GAPA, FBA, FBP, TIM, TKT, RPK, SEBP, RPI and RPE) [23].In cotton, a 25 µmol/L melatonin pretreatment promoted seed germination and improved the photosynthetic effect of seedlings [24,25].In tomato, melatonin treatment promoted growth and development, improved chlorophyll content and photosynthetic efficiency and up-regulated the chlorophyll synthesis genes POR, CAO and CHL G [26].
In summary, previous studies have proved that plant photosynthesis is affected by roots, and melatonin plays an important role in regulating root growth and photosynthesis.However, the effects of rhizome growth on photosynthesis and the role of melatonin in this process are still unclear in Leymus chinensis rhizomes.We hypothesized that there was a certain relationship between rhizome growth ability and photosynthesis of different Leymus chinensis, and exogenous melatonin treatment could affect aboveground growth and photosynthesis of Leymus chinensis by regulating rhizome growth.To address this hypothesis, we investigated the following aspects: (1) the relationship between rhizome growth capacity and aboveground growth and photosynthesis; (2) the effects of exogenous melatonin treatment on rhizome growth ability and aboveground growth; (3) whether exogenous melatonin affects aboveground growth and photosynthesis by regulating rhizome growth.To the best of our knowledge, this is the first systematic exploration of the relationship between rhizogenesis and aboveground growth and photosynthesis in Leymus chinensis and the role of melatonin in this process.This study further explores how rhizome growth influences photosynthesis and the regulatory mechanisms of melatonin.

Study Area, Plant Materials
The study was conducted in a controlled environment (a growth chamber) at the College of Grassland Science, Shanxi Agricultural University, Shanxi province, China.As depicted in Table 1, nine Leymus chinensis locations were utilized in this study.

Experimental Design and Treatment Management
The experiment was conducted using a completely randomized design for pot experiments, in which plants were cultivated in an intelligent lighting room environment in Shanxi, China.We had nine Leymus chinensis from different geographical locations (Table 1) and transplanted them into pots with inside diameter (15 cm), outside diameter (21 cm) and height (17 cm) filled with nutritive soil of the same quality (sand: vermiculite = 3:1), with five plants per pot, and for each material, four separate biological tests were conducted, totaling 36 pots.During the cultivation period, pots were watered with 500 mL of water every four days and rotated to ensure consistent lighting.After seven weeks of cultivation, the growth traits of aboveground and underground were measured, and fresh leaves were selected for the measurement of photosynthesis and chlorophyll content.
Based on the measured growth traits of the rhizomes, we selected one material each with strong and weak rhizome growth ability for transplantation and cultivation for another seven weeks before beginning melatonin treatments.The concentrations of exogenous melatonin treatment were 0 (CK), 100, 200, 300, 400 and 500 µmol/L [27].Melatonin was applied by watering 500 mL in the evening every four days, with a total of four treatments.Subsequently, the growth traits of aboveground and rhizomes were measured again, along with photosynthesis and chlorophyll content.

Experimental and Analytical Procedures 2.3.1. Determination of Traits of Aboveground and Rhizomes
We measured both aboveground and underground traits.Aboveground traits included plant height, stem thickness, stem length, number of leaves, leaf length, leaf width and the product of leaf length and leaf width (LL × LW).Underground traits included root length, root thickness, number of extravaginal ramets and clonal growth rate.The methods for determining the aboveground and underground (rhizome) traits are as shown in Table 2.The test material was assessed from 9:00 to 11:00 in the morning and each assessment was conducted three times consecutively.A CIRAS-4 portable photosynthesizer (PP SYS-TEMS, USA) was utilized to measure the following indices: net photosynthetic rate (Pn: , transpiration rate (Tr: mmol•m 2 •s −1 ) and water use efficiency (WUE: µmol•mmol −1 ).During the measurements, three plants showing robust growth were randomly selected for each treatment, and the flag leaves were examined.
Chlorophyll content: The SPAD-502 chlorophyll content tester was employed to measure the chlorophyll content of the third leaf beneath the flag leaf, and the average value was obtained from three measurements.The SPAD value provided by the SPAD-502 instrument is derived from the principle of light absorption and reflection.It converts the light absorbed by chlorophyll into an electrical signal, which is then processed by a microprocessor to calculate the relative chlorophyll content, expressed as the SPAD value.

Statistical Analyses
Data was sorted out through Microsoft Office Excel 2021, Origin 2022 was used for plotting, the R language was used for principal component and cluster analysis, ggplot2 and the corrplot package were used for plotting, and SPSS26.0 was used for univariate analysis of variance (ANOVA).The least significant difference (LSD) method was used for multiple comparisons.All data are expressed in the form of mean ± standard error.

Aboveground Growth of Leymus chinensis
As shown in Table 3, the results of descriptive statistics and ANOVA for the aboveground growth traits of Leymus chinensis indicated significant differences among all seven traits (p < 0.05).The top three plant heights were LC19, LC14 and LC44.The top three stem thickness were LC19, LC62 and LC44.The top three stem length were LC23, LC19 and LC2.The top three leaf lengths were LC44, LC14 and LC19.The top three leaf widths were LC14, LC19 and LC2.The top three leaf numbers were LC19, LC44 and LC14.The specific leaf area was highest in LC14, followed by LC44 and LC19.

Rhizome Growth of Leymus chinensis
The results of descriptive statistics and ANOVA for the rhizome traits of Leymus chinensis indicated significant differences among all four traits of the nine Leymus chinensis specimens (p < 0.05).As shown in Figure 1, the top three root lengths were LC23, LC19 and LC44.The top three root thicknesses were LC19, LC23 and LC44.The top three numbers of extravaginal ramets were LC19, LC23 and LC62.It is evident that LC2, LC13, LC14 and LC27 exhibit weak rhizome growth capability, while LC19 and LC23 demonstrate stronger rhizome growth capability.

The Relationship between Rhizome Growth and Above Ground Growth
As depicted in Figure 2, correlation analysis was performed on the seven aboveground growth traits and four rhizome traits of nine Leymus chinensis specimens.The results revealed a significant positive correlation between stem length and root thickness (p < 0.05), as well as between stem length and root length (p < 0.05).Additionally, plant height showed a significant positive correlation with root thickness (p < 0.01) and root length (p

The Relationship between Rhizome Growth and Above Ground Growth
As depicted in Figure 2, correlation analysis was performed on the seven aboveground growth traits and four rhizome traits of nine Leymus chinensis specimens.The results revealed a significant positive correlation between stem length and root thickness (p < 0.05), as well as between stem length and root length (p < 0.05).Additionally, plant height showed a significant positive correlation with root thickness (p < 0.01) and root length (p < 0.05).Moreover, root length exhibited a significant positive correlation with the leaf number of Leymus chinensis (p < 0.05).These findings suggest a strong relationship and positive effect between rhizome and aboveground traits.

Photosynthesis of Different Leymus chinensis
As shown in Figure 3, there were significant differences in the photosynthetic indices among the nine Leymus chinensis materials.The highest three chlorophyll contents (Figure 3A) were found in LC19, LC23 and LC14.The highest net photosynthetic rates (Figure 3B) were observed in LC19, LC44 and LC23.Stomatal conductance (Figure 3C) was highest in LC14, LC27 and LC2.For intercellular carbon dioxide concentration (Figure 3D), the top three materials were LC19, LC23 and LC27.The transpiration rate (Figure 3E) was highest in LC2, LC13 and LC62.Water use efficiency (WUE) (Figure 3F) was ranked highest in LC44, followed by LC23 and LC19.It is apparent that LC19, a material with strong rhizome growth ability, exhibited higher chlorophyll content, net photosynthetic rate and intercellular CO2 concentration, suggesting a correlation between the growth ability of this rhizome and photosynthesis.Conversely, for LC2, which has weak rhizome growth ability, these indices were lower.This suggests that the rhizome growth ability of Leymus chinensis may influence photosynthesis, indicating a relationship between them.

Photosynthesis of Different Leymus chinensis
As shown in Figure 3, there were significant differences in the photosynthetic indices among the nine Leymus chinensis materials.The highest three chlorophyll contents (Figure 3A) were found in LC19, LC23 and LC14.The highest net photosynthetic rates (Figure 3B) were observed in LC19, LC44 and LC23.Stomatal conductance (Figure 3C) was highest in LC14, LC27 and LC2.For intercellular carbon dioxide concentration (Figure 3D), the top three materials were LC19, LC23 and LC27.The transpiration rate (Figure 3E) was highest in LC2, LC13 and LC62.Water use efficiency (WUE) (Figure 3F) was ranked highest in LC44, followed by LC23 and LC19.It is apparent that LC19, a material with strong rhizome growth ability, exhibited higher chlorophyll content, net photosynthetic rate and intercellular CO2 concentration, suggesting a correlation between the growth ability of this rhizome and photosynthesis.Conversely, for LC2, which has weak rhizome growth ability, these indices were lower.This suggests that the rhizome growth ability of Leymus chinensis may influence photosynthesis, indicating a relationship between them.

The Relationship between Rhizome Growth and Photosynthesis
As shown in Figure 4, the correlation analysis of four rhizome traits and six photosynthetic indices of nine Leymus chinensis materials was conducted.The results showed a significant negative correlation between transpiration rate and root thickness (p < 0.05), as well as between transpiration rate and root length (p < 0.05).Chlorophyll content exhibited a significant positive correlation with root diameter (p < 0.001), CGR (p < 0.05), NER (p < 0.05) and root length (p < 0.01).Root thickness showed a significant positive correlation with WUE (p < 0.01) and Pn (p < 0.01).Additionally, root length demonstrated a significant positive correlation with WUE (p < 0.001) and Pn (p < 0.05).

The Relationship between Rhizome Growth and Photosynthesis
As shown in Figure 4, the correlation analysis of four rhizome traits and six photosynthetic indices of nine Leymus chinensis materials was conducted.The results showed a significant negative correlation between transpiration rate and root thickness (p < 0.05), as well as between transpiration rate and root length (p < 0.05).Chlorophyll content exhibited a significant positive correlation with root diameter (p < 0.001), CGR (p < 0.05), NER (p < 0.05) and root length (p < 0.01).Root thickness showed a significant positive correlation with WUE (p < 0.01) and Pn (p < 0.01).Additionally, root length demonstrated a significant positive correlation with WUE (p < 0.001) and Pn (p < 0.05).

Effects of Exogenous Melatonin Treatment on Rhizome Growth
According to the above results, we subjected LC19 and LC2 to exogenous melatonin treatment.LC19 exhibits strong rhizome growth ability, while LC2 shows weak rhizome growth ability.

Effects of Exogenous Melatonin Treatment on Aboveground Growth
As shown in Table 4, for LC2, the 200 µmol/L melatonin treatment increased plant height, stem thickness, stem length, leaf length, leaf width and leaf area by 24.31%, 11.10%, 26.75%, 19.94%, 29.23% and 43.30%, respectively, compared with the control treatment.With the 100 µmol/L melatonin treatment, the number of leaves increased by 14.38% compared to the control.For LC19, the 100 µmol/L melatonin treatment increased plant height and stem length by 12.60% and 46.32%, respectively, compared with the control treatment.The 200 µmol/L melatonin treatment increased stem thickness, leaf length, leaf width and leaf area by 34.76%, 82.54%, 29.44% and 87.84%, respectively, compared with the control treatment.

Effects of Exogenous Melatonin Treatment on Rhizome Growth
According to the above results, we subjected LC19 and LC2 to exogenous melatonin treatment.LC19 exhibits strong rhizome growth ability, while LC2 shows weak rhizome growth ability.

Effects of Exogenous Melatonin Treatment on Photosynthesis
As shown in Figure 6, the results of descriptive statistics and ANOVA for the photosynthesis of Leymus chinensis after melatonin treatment showed significant differences (p < 0.05).For LC2, the 500 µmol/L melatonin treatment increased Ci by 9.25% compared to the control treatment.The 300 µmol/L melatonin treatment increased Gs by 37.88%.Additionally, with the 300 µmol/L melatonin treatment, Pn, Tr and WUE increased by 63.40%, 28.17% and 48.79%, respectively, compared to the control treatment.Regarding LC19, the 100 µmol/L melatonin treatment increased Ci, Gs and Tr by 4.18%, 41.59% and 36.52%,respectively, compared to the control treatment.With the 400 µmol/L melatonin treatment, Pn and WUE increased by 48.37% and 51.97%, respectively.

Effects of Exogenous Melatonin Treatment on Aboveground Growth
As shown in Table 4, for LC2, the 200 μmol/L melatonin treatment increased plant height, stem thickness, stem length, leaf length, leaf width and leaf area by 24.31%, 11.10%, 26.75%, 19.94%, 29.23% and 43.30%, respectively, compared with the control treatment.With the 100 μmol/L melatonin treatment, the number of leaves increased by 14.38% compared to the control.For LC19, the 100 μmol/L melatonin treatment increased plant height and stem length by 12.60% and 46.32%, respectively, compared with the control treatment.The 200 μmol/L melatonin treatment increased stem thickness, leaf length, leaf width and leaf area by 34.76%, 82.54%, 29.44% and 87.84%, respectively, compared with the control treatment.

Effects of Exogenous Melatonin Treatment on Photosynthesis
As shown in Figure 6, the results of descriptive statistics and ANOVA for the photosynthesis of Leymus chinensis after melatonin treatment showed significant differences (p < 0.05).For LC2, the 500 μmol/L melatonin treatment increased Ci by 9.25% compared to the control treatment.The 300 μmol/L melatonin treatment increased Gs by 37.88%.Additionally, with the 300 μmol/L melatonin treatment, Pn, Tr and WUE increased by 63.40%, 28.17% and 48.79%, respectively, compared to the control treatment.Regarding LC19, the 100 μmol/L melatonin treatment increased Ci, Gs and Tr by 4.18%, 41.59% and 36.52%,respectively, compared to the control treatment.With the 400 μmol/L melatonin treatment, Pn and WUE increased by 48.37% and 51.97%, respectively.

Discussion
Melatonin treatment effectively regulates root growth and root structure.For example, 10 µmol/L melatonin can promote the root growth of the hypocotyl of white lupine (Lupinus albus) [28].Seed initiation with melatonin promotes seed germination and stimulates root growth and development [29,30].In studies on cucumber, exogenous melatonin treatment can activate lateral root generation and promote root growth by up-regulating the expression of 121 genes in the root [19,31].Exogenous melatonin can improve resistance to abiotic stress by promoting root growth [32].For example, in studies on cotton (Gossypium) and tomato (Solanum lycopersicum), exogenous melatonin treatment promoted root length, root surface area, root volume and specific root length of plants under drought stress, enhancing drought resistance and yield [19,[33][34][35].In this study, exogenous melatonin treatment effectively improved the rhizome growth of Leymus chinensis with different rhizome growth abilities, including root length, root thickness, root number and root clone growth rate.Simultaneously, it increased aboveground trait growth.However, high concentrations of melatonin have a growth-inhibiting effect.
The growth of roots will affect leaf growth and photosynthesis in the aboveground part [36,37].When researchers imposed root restriction, they found that it affected plant growth, physiological processes and yield [25].In some plants, root restriction reduces photochemical activity and chlorophyll content.For instance, in cayenne pepper, root restriction resulted in reduced plant height and total leaf area growth, thereby reducing the plant's ability to capture photosynthetically active radiation [38].With adequate water and nutrient supply, there was a significant correlation between leaf area and root growth and leaf area and bud growth depended on root size.In cotton, the leaf area and root dry matter production of cotton growing under restricted root conditions are limited and the photosynthetic rate is slightly lower.A decrease in the photosynthetic rate due to root restriction was observed in tomatoes [39].Some researchers found that root restriction reduced chlorophyll a, chlorophyll b and total chlorophyll in euonymus plants by nearly half, a reduction that may vary depending on the strength of the imposed root restriction [40].In this study, significant differences were observed in the growth and photosynthesis of aboveground parts of Leymus chinensis with different rhizome growth abilities.Correlation analysis found a significant positive correlation between rhizome growth ability and aboveground leaf growth and photosynthesis, which is consistent with the previous conclusion that the quality of root growth impacts photosynthesis and aboveground growth.
Chlorophyll is an indispensable pigment in plants and plays a vital role in photosynthesis.Related studies have found that melatonin inhibits the decomposition of chlorophyll under stress.For example, in rapeseed, exogenous melatonin treatment regulated root growth and alleviated the decomposition of chlorophyll and the reduction of chloroplast structure in seedlings under drought [41].Melatonin prevents the breakdown of chlorophyll, including PAO, PPH, RCCR, HCAR, NOL and NYC1, by down-regulating the expression of genes related to chlorophyll degradation and inhibiting the activity of enzymes involved in chlorophyll catabolism, such as CLH and PPH [32,42,43].In broccoli (Brassica oleracea L. var.), exogenous melatonin treatment down-regulated the expression of NYC1, NOL, CLH, PPH, PAO, RCCR and SGR1 involved in chlorophyll catabolic metabolism.Melatonin treatment also promotes the resynthesis of chlorophyll.The application of melatonin significantly upregulated the expression of genes related to chlorophyll synthesis such as POR, CAO and CHL G and increased the chlorophyll content [32].Current studies have shown that melatonin promotes chlorophyll renewal by regulating synthesis and degradation and maintains chlorophyll stability in the long term.In this study, the material treated with exogenous melatonin can effectively improve the growth ability of rhizomes and promote the chlorophyll content in leaves, while the chlorophyll content in leaves can be significantly reduced when the growth of rhizomes is inhibited by a high concentration, indicating that melatonin can affect the synthesis and degradation of chlorophyll by regulating the growth of rhizomes [44][45][46][47].In our study, there was a significant correlation between rhizome growth ability and aboveground growth and photosynthetic index.While melatonin treatment promoted root and stem growth, chlorophyll content, fluorescence parameters and photosynthetic efficiency of leaves were enhanced.This article provides a theoretical basis for exploring the effects of melatonin on aboveground growth and photosynthesis by regulating rhizome growth.In the future, the mechanism of melatonin regulation can be determined by targeting the molecular expression related to rhizomes and photosynthesis.

Conclusions
In this study, we systematically explored the relationship between rhizome growth ability, aboveground growth and photosynthesis of Leymus chinensis from different locations.There is a positive correlation between them.In particular, it is suggested that rhizome growth ability might affect and regulate aboveground growth and photosynthesis.The application of exogenous melatonin increased root length, root thickness, number of extravaginal ramets, clonal growth rate, etc., increased aboveground traits such as plant height, leaf length and leaf area, etc., and enhanced photosynthesis and chlorophyll content.However, high concentrations of exogenous melatonin can cause inhibition in rhizome growth and photosynthsis.In conclusion, rhizome growth ability affects aboveground growth and photosynthesis, and exogenous melatonin can affect aboveground growth and photosynthesis by regulating rhizome growth.

Figure 2 .
Figure 2. Correlation between rhizome growth indicators and aboveground growth indicators (red indicates a negative correlation between the two factors, blue indicates a positive correlation between the two factors, and the depth of the color indicates the strength of the correlation.* p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 2 .
Figure 2. Correlation between rhizome growth indicators and aboveground growth indicators (red indicates a negative correlation between the two factors, blue indicates a positive correlation between the two factors, and the depth of the color indicates the strength of the correlation.* p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 4 .
Figure 4. Correlation between rhizome growth ability and photosynthesis (red indicates a negative correlation between the two factors, blue indicates a positive correlation between the two factors, and the depth of the color indicates the strength of the correlation, * p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 4 .
Figure 4. Correlation between rhizome growth ability and photosynthesis (red indicates a negative correlation between the two factors, blue indicates a positive correlation between the two factors, and the depth of the color indicates the strength of the correlation, * p < 0.05, ** p < 0.01, *** p < 0.001).

Table 2 .
Methods for determination of Leymus chinensis traits.

Table 3 .
Statistics of aboveground character index of Leymus chinensis.

Table 4 .
Aboveground characters treated with exogenous melatonin.

Table 4 .
Aboveground characters treated with exogenous melatonin.