Introduction

Pinellia ternata (Thunb.) Ten. ex Breitenb., a perennial herbaceous plant of the Araceae family and the Areae tribe1,2, is primarily distributed in East Asian countries within the North Temperate Zone, such as China, Japan, and Korea. It is also found in Germany, the Netherlands, and the eastern United States, with the most extensive distribution in central and southeastern China (https://www.gbif.org/zh/species/8678824)3. P. ternata has been a commonly used medicinal plant in East Asia, with a history of medicinal use spanning thousands of years and significant medical value4. In addition, P. ternata is included in the pharmacopeias of China and Japan, with its rhizome being the medicinal part, known for the effects of " removing dampness to reduce phlegm, downbearing counterflow to stop hiccup, and dissolving lumps and resolving masses"5,6. Modern pharmacological studies have shown that it possesses anti-tumor, antibacterial, anti-inflammatory, and anti-epileptic pharmacological effects, with nucleosides and organic acids being its important active ingredients7,8. In recent years, P. ternata has also been discovered to be an important plant for treating and preventing COVID-19, further expanding its range of applications7. Investigations show that the global demand for P. ternata raw materials reached 7,000 tons, with a market size of 1 billion yuan, ranking it as the 7th among the top 10 Chinese medicinal materials exported9. Based on its unique medical characteristics and promising market prospects, P. ternata has become an important industrial crop in Southeast Asian countries, possessing immense economic value and social benefits, making significant contributions to global healthcare and livelihoods.

Currently, wild resources of P. ternata remain one of the primary sources for commercial products10. However, the overharvesting of wild resources, urbanization, and the misuse of herbicides have led to a steady decline in wild P. ternata populations11. In response, many regions have begun cultivating P. ternata artificially to protect wild resources, increase production, and meet the robust international market demand. Despite these efforts, the relatively recent history of artificial cultivation has resulted in limited experience and rudimentary management practices. Current cultivation practices for P. ternata often involve basic agricultural techniques that lack standardization, leading to inconsistent yields and quality. For instance, typical practices include simple planting methods without optimal consideration of propagule type and size, and planting depth, which significantly affect the crop’s performance. There is a scarcity of research on cultivation models, and the lack of a standardized approach has made it challenging to maintain consistent yields and quality of P. ternata. As the cornerstone of the P. ternata industry, the cultivation challenges have emerged as the primary hindrance to its growth.

P. ternata exhibits both sexual and asexual reproduction, with asexual reproduction being predominant due to the challenges associated with sexual reproduction. Sexual reproduction in P. ternata relies on the development of spathes, which only form on larger propagules (> 1.5 cm) and face difficulties in fertilization and seed formation12. Previous studies by our research group have revealed that the type, size, and planting depth of the propagule affect the coefficient of propagation (emergences of seedlings) and yield of P. ternata. Moreover, studies have indicated that planting depth and propagule size substantially impact the yield and quality of root crops, making appropriate planting depths and suitable propagule sizes crucial for crop emergence, growth, and organ development13,14,15. Currently, there is a limited amount of research on the effects of tuber size and planting depth on the emergence rate and yield of P. ternata16,17. However, these studies primarily utilized yield or agronomic traits as criteria for selecting suitable planting depths or tuber sizes without assessing the bioactive components of P. ternata, such as nucleosides and organic acids. More importantly, bulbils, which serve as the primary propagules, are often neglected in research, severely limiting their development and application. In this study, we hypothesize that there is an optimal combination of propagule type, size, and planting depth that will not only enhance the emergence rate and yield of P.ternata but also improve the content of its bioactive components.

To evaluate this hypothesis rigorously, four research questions were framed: (1) Do different propagule types differentially modulate seedling emergence, agronomic performance, yield, and secondary-metabolite profiles in P. ternata (2) What propagule size maximizes tuber biomass while concurrently optimizing nucleoside and organic-acid concentrations (3) How does planting depth affect propagation coefficient, yield, and quality attributes (4) Which specific combination of propagule type, size, and planting depth provides a synergistic enhancement of emergence, productivity, and bioactive-metabolite accumulation?

Given this, the present study utilized the bulbils and tubers of P. ternata as materials for a one-year planting experiment involving multiple samples, various planting factors, and multiple replications. The primary objective was to elucidate the effects of different planting depths as well as the type and sizes of the propagules on the seedling emergence (propagation coefficient), agronomic traits, yield, content of nucleoside components, content of organic acid components, and the content of extractives in P. ternata. The aim was to develop an efficient cultivation mode for P. ternata, which is of considerable importance for the sustainable development of the P. ternata industry.

Materials and methods

Plant material

Propagules, including tubers and bulbils of P. ternata, were purchased from the producing area in Qianjiang (30o26’1’’N, 112o47’23’’E). It was identified by Professor Dahui Liu from Hubei University of Chinese Medicine as the plant P. ternata from the Araceae family; the varieties are shown in Figure 1. The tubers are categorized into three size grades: T1 (2.0–1.6 cm), T2 (1.4–1.2 cm), and T3 (1.0–0.8 cm). The bulbils are divided into two size grades: B1 (1.0–0.8 cm) and B2 (0.8 –0.6 cm).

Planting

The experiment was conducted from December 2021 to December 2022 at the Medicinal Plant Garden of Hubei University of Chinese Medicine in Wuhan, Hubei Province, located at latitude 30°27′6″N and longitude 114°15′51″E. The area falls within a subtropical monsoon humid climate zone, with an elevation of 20 m, an average annual temperature of 19.5 °C, an average annual sunshine duration of 1741.4 h, and an average annual precipitation of 1260 mm. The terrain is flat and well-arranged, suitable for the growth of P. ternata. A randomized complete block design was employed: the experiment was set up with four planting depths of 5 cm, 10 cm, 15 cm, and 20 cm, and utilized five types of propagation materials as detailed in  “Plant material”, creating 20 different experimental groups with three replicates each (Fig. S1). In the experimental pots, 36 experimental materials were planted, three rows were set up, each row spaced 9 cm apart, with 12 propagules per row spaced 4.5 cm apart. During the growth of P. ternata, pest, disease, and weed control were managed in accordance with conventional field practices.

Determination of agronomic traits and extract content

Seven indicators, including agronomic traits and extractable content, were measured using the following methods: (1) Seedling emergence: After the emergence of P. ternata seedlings is completed in late April and August 2022, count the number of seedlings in the experimental plots (Seedling emergence = Number of seedling petioles/number of propagules); (2) Leaf length: After P. ternata stops growing in June 2022, measure the length of the middle split leaf blades; (3) Leaf width: After P. ternata stops growing in June 2022, measure the width of the middle split leaf blades; (4) Plant height: After P. ternata stops growing in late June 2022, measure the height of the plant; (5) Petiole diameter: After P. ternata stops growing, in June 2022 measure the diameter of the petiole at the middle part; (6) Yield (biomass): After P. ternata falls over (late November 2022), collect the tubers and bulbils, cleaning them of soil, and then weighing them. (7) Extract content: The measurement was conducted using the cold maceration method as recorded in General Rules 2201 of the 2020 edition of the Chinese Pharmacopoeia5. The measurements of the aforementioned agronomic traits were all taken using a vernier caliper.

Determination of nucleoside

Based on previously published research18, we identified six nucleoside components of tubers in P. ternata, and their contents were determined using high-performance liquid chromatography (HPLC). The HPLC analysis was conducted on an Agilent 1260 HPLC system. Separation was achieved on a column (Agilent XDB-C18, 4.6 mm × 250 mm, 5 μm) at a constant flow rate of 1 mL/min at 25 °C. To determine the contents of uracil, hypoxanthine, uridine, inosine, guanosine, and adenosine, the mobile phase consisted of water (A) and acetonitrile (B) with a gradient elution program as follows: 0–10 min, 0.5–2% B; 10–20 min, 2–3.5% B; 20–30 min, 3.5% to 10% acetonitrile; 30–50 min, 10% to 28% acetonitrile; 50–55 min, 28% to 30% acetonitrile; 55–60 min, 30% to 0.5% acetonitrile. The injection volume was 10 µL, and the monitored wavelength was 260 nm. The results of the standard measurements are shown in Fig. S2. Regression equations were established with the concentration of each component on the x-axis and the peak area integral values (w) on the y-axis, as shown in Table S1.

Determination of organic acid

Based on previously published research by Wei et al. (2024)19, we identified five organic acids, including malic acid, succinic acid, citric acid, cis-aconitic acid, and fumaric acid, from the tubers of P. ternata, and their contents were determined using HPLC-MS. The analysis was conducted on an Agilent 1260 HPLC system coupled with an Agilent Ultivo triple quadrupole mass spectrometer. Separation was performed on a column (Agilent ZORBAX Eclipse Plus C18, 100 mm × 2.1 mm, 1.8 μm) at a constant flow rate of 1 mL/min at 25 °C. For separating these chemical components, the injection volume was two µL, and the mobile phase consisted of 1% formic acid in water (A) and acetonitrile (B) with 5% B isocratic elution. The electrospray ionization source was operated in negative ion mode, and multiple reaction monitoring mode was used to detect the five organic acids simultaneously. Additionally, the drying gas temperature was set to 325 °C with a flow rate of 8 L/min; the sheath gas temperature was 350 °C with a flow rate of 11 L/min; the nozzle voltage was 45 psi, and the spray voltage was 3839 V. Table S2 presents the mass spectrometry parameters and regression equations.

Data analysis

Statistical analyses were performed using GraphPad Prism version 10.4.0. The data were analyzed to assess the effects of propagule type, size, and planting depth on the propagation coefficient, agronomic traits, yield, and quality of Pinellia ternata. The following statistical methods were employed: (1) Correlation Analysis: Import the mean values of propagule size, planting depth, agronomic traits, yield, extractable content, nucleoside components, and organic acid components into Statistic 26, and perform Pearson correlation analysis with a two-tailed significance test. The resulting data is then imported into Chiplot (https://www.chiplot.online/) to create a correlation heatmap. In this analysis, propagule size and planting depth were considered as independent variables, while agronomic traits, yield, and bioactive component content were considered as dependent variables. (2) Multifactorial ANOVA: A multifactorial analysis of variance (ANOVA) was conducted to evaluate the significant variations in planting depth and propagule size. The ANOVA included planting depth and propagule size as independent factors and the various agronomic traits and yields as dependent variables.

Results

The emergence rate of P. ternata seedlings under different planting depths and propagule sizes

The plants, bulbils, and tubers of P. ternata are shown in Fig. 1. Bulbils and tubers of different sizes were selected as propagules for planting experiments in this research. Two major peaks of seedling emergence were observed within the cultivation cycle, occurring in April and August, while two main peaks of seedling lodging were noted in June and November. Detailed records of the emergence status of P. ternata were kept monthly throughout the entire cultivation period, with the data presented in Fig. 2. This study found that the planting depth had no significant impact on the emergence rate of the tubers in the T1 group; however, it was negatively correlated with the number of seedlings in the other planting groups. Further analysis indicated that under all examined planting depths, the T1 group had the highest number of seedlings, followed by the T2, T3, and B1 groups, while the B2 group had the fewest seedlings.

At a planting depth of 5 cm, all sizes of propagules were able to germinate successfully. Among them, the T1 group showed the highest emergence of seedlings, while the B2 group showed the lowest. The emergence of seedlings for the T2, T3, and B1 propagules was relatively balanced, indicating that under shallow planting conditions, there is no significant difference in the emergence of seedling numbers between tubers and bulbils of the same size. It is worth noting that larger tubers germinated earlier and also lodged earlier. Moreover, with increasing planting depth, the emergence of seedlings for all tubers showed a declining trend, demonstrating a negative correlation between the emergence of seedlings and planting depth, with smaller-sized tubers being more affected by planting depth and having fewer emergences of seedlings. At a planting depth of 10 cm, the larger-sized T1 and T2 group tubers were less affected by planting depth, showing their stronger tolerance to deep planting, while the emergence of seedlings of other sizes of propagules was more significantly impacted. When the planting depth reached 15–20 cm, the emergence of seedlings for B1 and B2 grade bulbils was very low, or they failed to germinate at all, indicating that this depth is unsuitable for planting smaller-sized P. ternata. However, at a planting depth of 15 cm, the T3 group tubers still had a certain number of emergences of seedlings, indicating that tubers have a stronger tolerance to deep planting than bulbils under the same size conditions. After the first emergence, the emergence of seedlings in the second emergence period was significantly higher than in the first, and September was the period with the highest emergence of seedlings for P. ternata. Overall, the results from the entire cultivation cycle indicate that the emergence of seedlings of P. ternata is positively correlated with the size of the tuber and negatively correlated with planting depth. Tubers, as propagation materials, have a more substantial tolerance to deep planting than bulbils.

The main phenotypic traits of P. ternata under different planting depths and propagule sizes

During the peak seedling period in June 2022, groups with fewer than five seedlings were excluded (15B2, 20T3, 20B1, 20B2), and a statistical analysis of the main phenotypic traits of the remaining groups of P. ternata was conducted. The data on the main phenotypic traits of P. ternata under different planting depths and propagule sizes were analyzed using GraphPad Prism version 10.4.0. As illustrated in Fig. 3, the results showed that the agronomic traits of P. ternata have a significant positive correlation with the size of the propagules, and no significant correlation was found with planting depth. Under the same depth conditions, propagules with larger diameters significantly outperformed those with smaller diameters in leaf length, plant height, and petiole diameter. However, the T1 group of tubers reached the maximum leaf width at the same planting depth, while other groups did not show significant differences in leaf width. The impact of different planting depths on the four agronomic traits varied; plant height significantly decreased with increasing planting depth, while leaf length and width did not significantly change with depth. The petiole diameter showed little variation across different depths but tended to increase with greater planting depth.

Fig. 1
figure 1

P. ternata plants and propagation materials. A P. ternata plants; B leaf bulbil; C stem bulbil; D tuber.

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Fig. 2
figure 2

Seedling emergence of P. ternata at different sowing depths for various particle sizes. A The number of seedlings of different particle sizes of P. ternata at a depth of 5 cm; B The number of seedlings of different particle sizes of P. ternata at a depth of 10 cm; C The number of seedlings of different particle sizes of P. ternata at a depth of 15 cm; D Number of P. ternata seedlings of different particle sizes at a depth of 20 cm. T1: tubers size in 2.0–1.6 cm; T2: tubers size in 1.4–1.2 cm; T3: tubers size in 1.0–0.8 cm; B1: bulbils size in 1.0–0.8 cm; B2 bulbils size in 0.8 –0.6 cm.

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Fig. 3
figure 3

Main agronomic traits of P. ternata at different planting depths and particle size levels. A Leaf length; B leaf width; C plant height; D petioles diameter.

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The yield and extract content of P. ternata under different planting depths and propagule sizes

Among the sample groups with yields exceeding 10 g (as seen in Fig. 4A), after excluding the 15B1, 15B2, 20T3, 20B1, and 20B2 samples, an analysis was conducted on the yield and extractable content of propagules at different depths. The study results indicated that yield is negatively correlated with planting depth and positively correlated with the size of the propagules. The yield and extractable content were measured at the end of the growth period in late November 2022, after the plants had lodged and the tubers were harvested.

As shown in Fig. 4B, Group T1 demonstrated a significant advantage over other groups under the 5 cm planting depth condition. The yield of the tuber groups T2 and T3 was higher than that of the bulbil groups B1 and B2. Although there were differences in particle size between groups T2 and T3 at planting, their final yields were similar, as were the yields of groups B1 and B2. Moreover, the smallest B2 grade bulbils could yield a high output, significantly contributing to the overall yield increase. Under the 10 cm planting depth condition, the size of the propagules had a more pronounced effect on yield, with the larger propagules showing a more pronounced tolerance to deep planting. The yield of group 10T1 was higher than that of 5T1, indicating that the largest T1-grade tubers are more suitable for planting at a depth of 10 cm. For other groups, as the diameter of the propagules decreased, the yield gradually decreased, and all were lower than the yields under the 5 cm planting depth. Under the 15 cm and 20 cm planting depth conditions, the yield of T1 changed little but was lower than the yields under the 10 cm and 5 cm planting depths. For other groups, as the particle size decreased, the yield dropped sharply, indicating that depths of 15 cm and 20 cm are not suitable for cultivating P. ternata.

In this study, the content of extractable matter in all experimental groups of P. ternata exceeded the minimum standard of 7.5% as stipulated by the Chinese Pharmacopoeia, with an average extractable content of 16.04%, as shown in Fig. 4C. The results indicated that when the planting depth was 5 cm, the extractable content of P. ternata reached its highest value of 17.49%, whereas at a planting depth of 10 cm, the extractable content dropped to its lowest at 15.09%. Furthermore, at planting depths of 15 cm and 20 cm, the average extractable content of P. ternata was 15.21% and 16.03%, respectively. Further analysis revealed that both the B1 and B2 groups exhibited higher levels of extractable content regardless of whether they were planted at depths of 5-10 cm.

The contents of nucleoside components of P. ternata under different planting depths and propagule sizes

This study conducted a quantitative analysis of nucleoside components in P. ternata, with detailed data in Table 1. The analysis revealed significant differences in the content of the six measured nucleosides. The nucleoside components were measured at the end of the growth period in late November 2022, after the plants had lodged and the tubers were harvested.

Table 1 Content of nucleoside components in P. ternata at different cultivation modes.
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Specifically, the contents of uridine, guanosine, and adenosine were relatively high, with average contents of 154.88 µg/g, 143.91 µg/g, and 95.84 µg/g, respectively. In contrast, uracil had the lowest content, with an average of only 8.50 µg/g, while hypoxanthine and inosine had contents of 13.36 µg/g and 20.58 µg/g, respectively. Among all the sample groups, the 10T1 group had the highest total nucleoside content, reaching 675.17 µg/g, followed by the 10B2 group and the 5B2 group, with total contents of 537.88 µg/g and 512.07 µg/g, respectively. Conversely, the 20T2 group had the lowest total nucleoside content, with a sum of the six nucleosides at 285.13 µg/g.

The study clarified the impact of planting depth on the accumulation of nucleoside components in P. ternata. The sample group with a planting depth of 10 cm had the highest accumulation of nucleoside components, reaching 518.09 µg/g, followed by the sample group with a planting depth of 5 cm, with an average total nucleoside content of 471.11 µg/g. Subsequently, the sample groups with planting depths of 15 cm and 20 cm had total contents of 337.00 µg/g and 299.60 µg/g, respectively. The results indicated that most nucleoside components, including uracil, uridine, guanosine, and adenosine, exhibited a trend of increasing and then decreasing with the increase in planting depth, peaking at a planting depth of 10 cm. However, the content of hypoxanthine gradually decreased with increasing planting depth. These findings reveal that the accumulation of nucleoside components in P. ternata is significantly affected by planting depth and particle size, with the total content of the six nucleosides reaching its maximum value at a planting depth of 10 cm.

The contents of organic acid of P. ternata under different planting depths and propagule sizes

The content of organic acids in P. ternata varies significantly, with citric acid being the highest, followed by succinic acid and malic acid, while fumaric acid and cis-aconitic acid have the lowest content, as shown in Table 2. The organic acid components were measured at the end of the growth period in late November 2022, after the plants had lodged and the tubers were harvested.

Table 2 Content of organic acid components in P. ternata at different cultivation modes.
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The experimental results indicate that the group with a planting depth of 10 cm has the highest total accumulation of the five organic acids, with an average total content of 20.61 µg/g, followed by the group with a planting depth of 5 cm, with an average total content of 19.62 µg/g. The groups with planting depths of 15 cm and 20 cm have the lowest contents, with average totals of 14.81 µg/g and 17.82 µg/g, respectively.

In the groups where tubers were used as propagules, the propagules of size T2 (1.2–1.4 cm) showed a specific advantage at different depths. Furthermore, at a planting depth of 5 cm, the average total content of the T2 group was 20.16 µg/g, which was higher than that of the T1 and T3 groups. The same situation occurred in groups with planting depths of 10 cm and 15 cm. It was found that under the same depth, the content of the five organic acids changed with the size of the particle diameter, increasing first, peaking at T2, and then decreasing.

Correlation analysis

This research unveiled the correlations among propagule size, planting depth, agronomic traits, yield, extractable content, nucleoside components, and organic acid components (Fig. 5). It was found that propagule size has a significant positive correlation with agronomic traits. However, its impact on chemical components is variable, mainly showing a significant positive correlation with succinic acid content. Planting depth affected the chemical composition of P. ternata significantly, with a significant negative correlation observed between planting depth and the content of fumaric acid, malic acid, hypoxanthine, guanosine, and inosine in the plant.

Furthermore, this research indicated a slight correlation between agronomic traits and chemical components, such as a negative correlation with fumaric acid, citric acid, guanine, adenosine, and extractable content and a positive correlation with succinic acid, cis-aconitic acid, and inosine, but these correlations were not significant. Notably, petiole diameter showed a negative correlation with almost all chemical components. Among organic acids, citric acid and cis-aconitic acid were positively correlated with the content of other organic acids. And fumaric and malic acid were positively correlated with the content of most alkaloids. The alkaloid chemical components did not show specific correlation information, but it is worth noting that, except for uracil, the rest of the alkaloids were significantly negatively correlated with planting depth. Extractable content showed a negative correlation with propagule size, planting depth, and agronomic traits, but the correlations were not significant. Yield showed a significant positive correlation with propagule size and all agronomic traits and a negative correlation with planting depth, but the correlation was not significant.

Fig. 4
figure 4

A Yield of P. ternata at different planting depths and particle size grades; B statistics of yield; C statistics of leachate content.

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Fig. 5
figure 5

The correlations among particle size, planting depth, agronomic traits, yield, extractable content, nucleoside components, and organic acid components.

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Discussion

The type of propagule, its size, and planting depth can broadly influence the growth and development of various plants20,21. Thus, it is of significant importance for the industrial production of P. ternata to determine the appropriate type and size of propagules, as well as the corresponding planting depth.

The research demonstrated that different types of propagules significantly affect the yield of P. ternata, with tuber yields being markedly higher than those of bulbils. It’s important to note that bulbils can be categorized into stem and leaf bulbils, which, as crucial elements of asexual reproduction, possess considerable potential for application. In the natural environment, once mature, bulbils naturally detach and, upon entering the soil, facilitate propagation22. Therefore, in the cultivation of P. ternata, it is recommended to select varieties that include bulbils to fully exploit the benefits of asexual reproduction, thereby enhancing the propagation efficiency and yield of P. ternata.

The study reveals that the type and size of propagule and planting depth can significantly influence the growth and development of various rhizomatous plants, including P. ternata23. It is crucial to select larger bulbils or tubers as propagules to enhance the propagation efficiency and yield of P. ternata. Research indicates that larger propagules can significantly improve the emergence of seedlings of P. ternata, a result that aligns with previous studies24. This phenomenon may be attributed to the fact that larger propagules typically contain richer nutrient reserves, providing ample energy and material foundations for initial growth and development, thereby promoting rapid sprouting and emergence25,26. Furthermore, larger propagules can reach their maximum biomass more quickly, and under high-density planting conditions of P. ternata, the reduction in aboveground biomass is lower compared to smaller propagules27,28. Additionally, studies have pointed out that plants derived from larger tubers have a stronger competitive ability compared to those from smaller tubers. This could be because plants from larger propagules have better adaptability and recovery capabilities under adverse conditions, thus exhibiting stronger competitiveness29,30. Moreover, plants from larger propagules also have more developed root systems, enhancing their ability to absorb nutrients31.

The research findings indicate that the size of propagules has a significant positive impact on agronomic traits and yield. Specifically, larger propagules tend to show higher emergence of seedlings and tillering capabilities, and they exhibit superior characteristics in terms of agronomic traits, such as increased leaf area32,33. These traits contribute to enhanced photosynthetic efficiency and biomass accumulation34, which are directly correlated with the yield of P. ternata.

This study reveals that P. ternata is best suited to shallow planting depths, a finding that aligns with the characteristic of its shallow root system35. As the planting depth increases, the emergence of seedlings and yield of P. ternata significantly decrease, consistent with previous research17,36. Furthermore, this study revealed that intense planting leads to uneven and delayed emergence of seedlings, similar to the findings of Xiao et al. (2000)16. A possible explanation is that significant changes in planting depth can markedly alter the abiotic conditions of P. ternata cultivation, including oxygen, temperature, moisture, and soil, all of which are not conducive to the formation of suitable conditions for the emergence of seedlings37,38. On the other hand, increased planting depth may also directly inhibit the growth of P. ternata propagules. Given the limited nutritional reserves stored in P. ternata propagule, excessive nutrient consumption during emergences of seedlings and emergence could lead to insufficient nutrient supply after the propagule has germinated, resulting in weak seedlings39, which is consistent with previous research17, which found that propagules with a diameter greater than 2 cm of P. ternata can tolerate deeper planting but result in poor seedling conditions. Additionally, smaller rhizomes may exhaust all stored carbohydrates before the new shoots reach the soil surface, increasing the risk of plant regeneration and thus affecting the emergence of seedlings40. The difficulty in the emergence of seedlings observed in this study for 15B1/B2/20T3/B1/B2 also confirms this point.

It is worth noting that a planting depth that is too shallow may cause bulbils to emerge above the ground, and after lodging, they may remain on the ground without soil cover, affecting reproduction efficiency. Therefore, to enhance reproduction efficiency and the yield of P. ternata, attention should be paid to its growth cycle, especially after the lodging periods (April and August), when immediate soil covering should be carried out.

One of the quality control indicators for P. ternata is the content of water-soluble extractives according to the regulations of the Chinese Pharmacopoeia, which may include organic acids, saponins, alkaloids, sugars, amino acids, and proteins, among other components. This study showed that as the planting depth increases, the content of extractives tends to decrease, a phenomenon also confirmed by two other indicators. Alkaloids and organic acids, as key bioactive components of P. ternata, show a significant negative correlation with planting depth for most of their chemical constituents. It is speculated that increased planting depth leads to reduced soil permeability, affecting the respiratory function of the crop’s root system. Given the close relationship between the synthesis of nucleosides and organic acids and plant metabolic activities, insufficient soil permeability may limit these metabolic processes, thereby negatively impacting the synthesis of these components41. Moreover, the temperature in deeper soil layers is typically lower than in the topsoil, and temperature is a key factor affecting enzyme activity and metabolic reactions42. Lower soil temperatures may slow the biosynthesis rate of nucleosides and organic acids. To ensure the quality and yield of P. ternata, it is recommended to use shallow planting.

Bulbils, as a key organ for the propagation of P. ternata, play an indispensable role. Given the impact of genetic diversity on P. ternata, some varieties may lack bulbils or have low bulbil activity. Hence, screening for varieties with superior bulbil characteristics holds significant potential value for improving the production efficiency of P. ternata. Furthermore, previous studies have revealed that during the growth process of P. ternata seeds, the fresh weight of the plant shows an increasing and then decreasing trend, while the fresh weight and diameter of the tubers exhibit an “S” shaped change pattern over time43. Based on the actual observation of the growth dynamics of P. ternata, determining the appropriate planting and harvesting periods has become a research topic that requires in-depth exploration.

Conclusion

This study analyzed the impact of different types and sizes of P. ternata propagules, as well as planting depth, on the propagation coefficient, agronomic traits, yield, and quality of P. ternata by planting experiments, contributing to the development of efficient cultivation patterns for P. ternata. Tubers outperformed bulbils regarding propagation coefficient, agronomic traits, yield, and quality; larger propagules also performed better than smaller ones in the abovementioned aspects. Additionally, the study revealed the adaptive relationship between the yield and quality of P. ternata propagules of different particle sizes and planting depth, with the optimal planting depth for small-sized (≤ 1.6 cm) propagules being 5 cm. For larger-sized (1.6–2.0 cm) propagules, the optimal planting depth is 10 cm, at which the highest propagation coefficient, yield, and quality can be achieved. Furthermore, the propagation coefficient, yield, and quality of P. ternata are negatively correlated with planting depth and positively correlated with the size of the propagules. In summary, this research provides valuable insights into the scientific cultivation of P. ternata, aiding in its industrial development and benefiting growers, traders, and consumers alike.