Introduction

In modern agriculture, maximizing productivity per unit area for crops grown for production is emerging as a critical issue. Attaining this efficiency is contingent upon the health and robust development of plant materials utilized in cultivation (Korkmaz et al. 2023). To develop effective strategies that can overcome the challenges posed by limited arable land, it is essential to holistically understand the factors affecting plant growth and development (Dogan et al. 2022). In the pursuit of sustainable plant production practices aimed at enhancing efficiency and quality, recent studies indicate the pivotal role of Humic Acid (HA). Some researchers have reported the positive effect of humic acid (HA) on plant biomass, yield, and overall quality (Saidimoradi et al. 2019). One notable attribute of HA is its capacity to exert a buffering effect within a broad pH range in the soil, facilitating plant development by rendering various mineral elements more readily available to plants (Li et al. 2019). Furthermore, the application of humic substances, as elucidated by Canellas et al. (2015), goes beyond mere nutritional enhancement. It significantly contributes to soil improvement by enhancing aeration and water retention capacity. This multifaceted improvement in soil structure, in turn, translates into heightened resilience of plants under diverse stress conditions, including but not limited to drought, heat, diseases, and pests. Notably, the mechanism by which humic substances foster this resilience is intricately tied to their role in supporting the development and proliferation of soil microorganisms (Jing et al. 2020). On the other hand, the contemporary surge in the utilization of silicone has drawn significant attention, particularly within the realm of environmental stress studies on plants. Investigations conducted by Dehghanipoodeh et al. (2018), consistently affirm that silicon (Si) plays a crucial role in augmenting plant resistance. Remarkably, Si has the capacity to accumulate in concentrations comparable to macroelements such as nitrogen (N), potassium (K), magnesium (Mg), phosphorus (P), calcium (Ca), among others, essential for optimal plant growth (Ahire et al. 2021). Empirical evidence, as elucidated by studies such as this by Emamverdian et al. (2018), highlights the multifaceted benefits of silicon application in plants. Notably, plants supplied with sufficient Si exhibit reduced water loss, indicative of the role of silicon in mitigating transpirational stress. Additionally, Si accumulation has been identified as a contributing factor to bolstering the plant’s resilience against certain fungal diseases and insect-induced damage (Aras and Esitken 2018).

Apricots, a globally cultivated deciduous species, especially in Mediterranean countries, have become an indispensable commodity for producers, contributing significantly to both domestic and international markets (Torrecillas et al. 2000). Beyond its economic importance, the apricot is beneficial for human health and nutrition, serving as a versatile fruit consumed in fresh and dried forms, boasting a rich vitamin and mineral content (Torrecillas et al. 2018). Despite the significance of apricots, there is a notable scarcity of comprehensive studies focusing on the developmental stages of apricot seedlings and the application of organic and inorganic materials during this crucial phase. The examination of apricot seedling development, along with the application of organic and inorganic materials during the seedling period, represents a crucial area of research. This pursuit aims not only to deepen our understanding of the fundamental processes influencing apricot seedling growth but also to address the current research gap in this field. Considering the limited studies available, it becomes imperative to conduct a comprehensive investigation into the physical and biochemical developments caused by various fertilizer applications in apricot seedlings. Therefore, the primary objective of the current research is to fill existing gaps in the literature by illuminating the interactions between apricot seedling development and organic and inorganic materials such as humic acid and silicon. Through this endeavor, we seek to provide valuable insights that can inform sustainable practices in apricot cultivation, ultimately optimizing the productivity and quality of this economically significant fruit crop. In this regard, we specifically examined the development of Alyanak, Şekerpare, and Hacıhaliloğlu apricot seedlings, exploring the impact of different HA, Si and their combinations supplied through irrigation water on various physiological, morphological characteristics and macronutrient contents.

Materials and Methods

Experimental Site and Plant Material

This research was conducted in the Department of Horticulture, Faculty of Agriculture, Harran University, during the period spanning January to August in 2019. The experimental subjects comprised seedlings of Alyanak, Şekerpare, and Hacıhaliloğlu apricot cultivars. Initially, the seeds underwent a pre-stratification water immersion of 2 days to facilitate water absorption. Following this hydration period, the seeds were extracted from the water and placed in perlite maintained at +4 °C in a refrigerated environment for approximately 2 months. Subsequently, the stratified seeds were transferred to containers containing peat for the germination phase. Uniform care was administered to ensure consistent seedling development across all specimens germinating in the containers. Apricot seedlings demonstrating homogeneous development were subsequently transplanted into 7 L plastic tubes, each filled with an equivalent weight of peat, in March. The composition of the peat employed as growth medium in the experiment adhered to specific ratios, namely 14:10:18 (N:P:K), with an electrical conductivity (EC) of 35 mS/m, a pH of 6.5, and a density of 1.0 kg/m3. Notably, the nutrient solutions utilized in the study incorporated Humic Acid (HA) at a concentration of 22% and Sodium Silicate (Na2SiO3), denoted as Si.

Experimental Treatments

The seedlings underwent uniform irrigation, fertilization (utilizing a 50% Hoagland solution), and a four-week acclimation period to foster adaptation to conditions. Moreover, the irrigation regimen implemented for the seedlings was tailored, considering the optimal moisture levels in the surroundings. Specifically, the irrigation scheme was designed to maintain an average consumption of 40% of the available moisture in the pots, following the methodology proposed by Düzdemir et al., (2009). On April 28, 2019, solution applications were initiated, wherein chemicals dissolved in water were administered to the plants through irrigation at 15-day intervals. These solutions encompassed single and combined applications of HA at a concentration of 10 Mm and Si at 10 Mm. The experimental design adhered to a split-plot trial design within random plots, with a total of 60 plants utilized, each serving as one plant in each of the five replications. The study encompassed three apricot cultivars (Alyanak, Şekerpare, and Hacıhaliloğlu) and four distinct application combinations, namely control, HA, Si, and HA + Si.

Plant Growth Parameters

The culmination of the experiment occurred with the removal of seedlings on August 28, 2019. Post-harvest, meticulous attention was given to the cleaning of seedling roots using water. Then, shoot and root samples were subjected to a drying process at temperatures ranging from 65 to 70 °C for a duration of 48 h. Plant growth parameters were then determined for each seedling, including root dry weight (RDW), root fresh weight (RFW), total plant fresh weight (TPFW), shoot fresh weight (SFW), total plant dry weight (TPDW), and shoot dry weight (SDW). Furthermore, shoot diameter (SD), shoot length (SL), and root length (RL) were measured at the experiment, aligning with established protocols (Bolat et al. 2016; Dogan et al. 2022). The determination of total plant leaf number (TLN) was achieved through the counting of each leaf collected from individual pots. leaf area (LA) measurements were conducted on leaves that had reached full development in the central portion of the shoot, employing photographic documentation (Bolat et al. 2022). The subsequent calculation of leaf area for plants across all combinations was executed in square centimeters using the ImageJ computer program, following the methodology proposed by Klamkowski and Treder (2008).

Physio-Biochemical Parameters

For all seedlings subjected to treatments, newly matured leaves at the mid-upper part of the shoots were identified. Measurements of stomatal conductance during daytime hours (12:00–14:00) were conducted using a ‘Leaf Porometer’ device (Decagon Devices Inc., Model SC‑1, Steady-State Diffusion Porometer, Nebraska, WA, USA), as detailed by Bolat et al. (2022). Additionally, the chlorophyll levels (middle part of the leaf blade) were determined using a SPAD-502 Plus device (Konica Minolta Optics, Inc., Tokyo, Japan), following the methodology established by Bolat et al. (2022). Leaf temperature measurements during midday hours (12:00–14:00) were carried out using an Infrared thermometer on newly developed leaves at the mid-upper part of the shoots, as outlined by Mancuso and Azzarello (2002).

Mineral Analysis in Leaves

The leaves were washed with distilled water and subsequently air-dried for 48 h at 65–70 °C in a controlled drying oven. The obtained dried leaves were then ground into powder using a mortar and pestle. The nitrogen (N) content levels of the samples were determined using the Kjeldahl procedure, while calcium (Ca), magnesium (Mg), and potassium (K) values were determined using atomic absorption spectrophotometry. The phosphorus (P) content of the samples was calculated using a spectrophotometer (Shimadzu UV-1700) (Kacar and Inal 2008; Bolat et al. 2022).

Statistical Analysis

Statistical analyses were conducted using Origin Pro software (Version 2023). The data underwent Two-Way ANOVA, and mean separations were performed utilizing Tukey’s test (p ≤ 0.05). Additionally, a Principal Component Analysis (PCA) and Pearson correlation matrix were generated using the Origin Pro software to enhance the interpretability and understanding of the relationships between variables.

Results

Plant Growth and Physiological Parameters

Figures 1 and 2 visually portray the effects of HA and Si applications on the growth parameters of Alyanak, Şekerpare, and Hacıhaliloğlu seedlings. The parameters, LA, TLN, SD, SL, and others, exhibited noticeable increases in response to HA and Si applications compared to the control group. Specifically, Alyanak Si (91.48 cm2) and Şekerpare HA + Si (88.14 cm2) applications resulted in the highest LA values. The control seedlings exhibited the lowest leaf area and no enhancement from treatments. HA treatment resulted in a significant increase in LA compared to the control. Si treatment alone also increased LA, but not as significantly as HA and indicated a less pronounced effect on leaf growth. The HA + Si treatment group showed the highest LA, and it demonstrated a synergistic effect when both treatments are applied together (Fig. 1a). The control seedlings again showed the lowest TLN. HA treatment increased TLN significantly over the control. Si alone had a modest impact on TLN, less than HA, implied that while beneficial, Si’s effect on TLN is not as strong as HA’s. The combination of HA and Si yielded the highest TLN, and it indicated a synergistic effect like what was observed with LA. Across both parameters (LA and TLN), the combination treatment (HA + Si) consistently showed the most significant improvement, highlighting the benefits of treatment interaction. HA appears to be more effective than Si when used alone, both in terms of promoting leaf area and increasing TLN (Fig. 1b). The control group presented a baseline SD, which was comparatively lower than the treatment groups. HA treatment showed an increase in SD, though not the highest. Si treatment appears to have a similar impact on SD as HA, without any significant difference between them. The HA + Si treatment group exhibited no significant increase over HA or Si alone (Fig. 1c). The SL in the control group was the lowest. HA treatment led to a moderate increase in SL. Si treatment did not significantly increase SL over the control. The combination of HA and Si showed a significant increase in SL compared to the control, HA alone, and Si alone. SL did not show a clear synergistic effect from HA and Si combined, as all treatments resulted in similar outcomes, which were nonetheless better than the control. SL, on the other hand, was significantly improved by the combination of HA and Si. The data suggest that while HA and Si individually contribute to root growth, their combination is particularly beneficial for enhancing the net assimilation rate (Fig. 1d). The control seedlings displayed the lowest RL. HA treatment resulted in a significant improvement in RL over the control. Si treatment did not significantly improve RL over the control. The combined HA + Si treatment showed a slight improvement in RL compared to HA alone, though this was not as pronounced as the difference between HA and control. HA shows a clear beneficial effect on RL, while Si did not demonstrate a significant increase in root length on its own. However, when combined with HA, Si contributed to a marginal increase in RL. In conclusion, HA is confirmed to be effective in promoting root elongation as evidenced by increased RL (Fig. 1e). The control seedlings served as the baseline for stomatal conductance with the lowest observed values. HA treatment significantly increased SC compared to the control, Si treatment also resulted in an increase in SC, but not to the same extent as HA. The HA + Si treatment group showed the highest SC. HA treatment did not result in a statistically significant increase in CI compared to the control. Si treatment similarly showed no significant difference from the control in terms of CI. The HA + Si treatment was not significantly improving CI over the control, HA, or Si treatments Stomatal conductance was significantly influenced by the application of HA and Si, particularly when used in combination, as shown by the highest SC values in the HA + Si treatment. In contrast, the chlorophyll index was not significantly affected by any of the treatments (Fig. 1g). Analyzing the total chlorophyll content in plants and averaging the measurements revealed distinct outcomes. The highest chlorophyll concentrations were identified in the Şekerpare HA + Si application (43.74) and Alyanak Si application (43.02) compared to the control group (Fig. 1h).

Fig. 1
figure 1

Distinct letters associated with each bar represent statistically significant variations among both cultivarsand treatments, as determined by Tukey’s multiple range test at a significance level of P ≤ 0.05. Significance levels are denoted as follows: * for P ≤ 0.05, ** for P ≤ 0.01, and *** for P ≤ 0.001. The abbreviations correspond to the following parameters: LA Leaf Area, TLN Total Leaf Number, SD Shoot Diameter, SL Shoot Length, RL Root Length, LT Leaf Temperature, Chl Chlorophyll Content, and SC Stomatal Conductance

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Fig. 2
figure 2

a Şekerpare, b Alyanak, c Hacıhaliloğlu; 1: Control, 2: HA, 3: Si, 4: HA + Si

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Treatments significantly influenced the growth parameters of different apricot cultivars. In terms of SFW, HA treatment (60.53 g) demonstrated a substantial increase compared to the control (46.21 g), Si treatment (59.63 g), and combined HA + Si treatment (60.84 g). Alyanak variety exhibited the highest SFW (62.60 g). For RFW, Alyanak variety (30.07 g) displayed the highest values, while Hacıhaliloğlu exhibited the lowest (14.08 g). The application of HA resulted in the highest TPFW (85.78 g), significantly surpassing other treatments, with Alyanak once again showing the highest TPFW (92.67). In terms of SDW, Alyanak (23.79 g) outperformed other varieties, and HA treatment yielded the highest SDW (24.56 g). Similar trends were observed for RDW, where Alyanak (7.60 g) and HA treatment (7.25 g) exhibited the highest values. TPDW mirrored the trends observed in SDW and RDW, with Alyanak (31.40 g) and HA treatment (31.82 g) recording the highest values. Two-Way ANOVA analyses indicated highly significant differences between treatments (p < 0.0001) and among apricot cultivars (p < 0.0001). The interaction between treatments and cultivars (T*V) did not yield statistically significant differences (Table 1).

Table 1 Variables and their abbreviations include: RFW (Root Fresh Weight), SFW (Shoot Fresh Weight), TPFW (Total Plant Fresh Weight), RDW (Root Dry Weight), SDW (Shoot Dry Weight), and TPDW (Total Plant Dry Weight) (g plant−1)
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Mineral Analysis in Leaves

The mineral content analysis of apricot leaves across different cultivars and treatments revealed significant variations in N, K, P, Mg, and Ca concentrations. Our results indicated substantial differences in these mineral levels (Table 2). N and P content was significantly affected by both treatment types (T) (p < 0.0001) and cultivars (V) (p < 0.0001). The HA treatment demonstrated the highest N content, with a mean value of 2.36%, followed by Si (2.13%) and HA + Si (2.12%). Among cultivars, Alyanak exhibited the highest N content (2.21%), while Hacıhaliloğlu had the lowest (2.11%). Besides, the highest P content was observed in Alyanak (0.38%) among cultivars. The HA treatment showed the highest P content (0.37%), followed closely by Si (0.36%) and HA + Si (0.33%). K content displayed significant differences only in response to treatment types (T) (p < 0.0001). The highest K content was observed in the Si treatment (4.10%), followed by HA + Si (4.26%) and HA (3.98%). Cultivars did not exhibit significant differences in K content. In addition, Mg and Ca content showed significant variations in response to both treatment types (T) (p < 0.0001) and cultivars (V) (p < 0.0001). The highest Mg content was observed in Alyanak (0.37%), and the lowest in Şekerpare (0.31%). Among treatments, Si and HA + Si treatments demonstrated the highest Mg content (0.39 and 0.33%, respectively). The highest Ca content was observed in Alyanak (1.35%), while the lowest was in Hacıhaliloğlu (1.08%). The HA treatment exhibited the highest Ca content (1.30%), followed by Si (1.29%) and HA + Si (1.11%). The interaction between treatments and cultivars (T*V) was significant for Ca content (p = 0.01293).

Table 2 The mineral content in the leaves of Şekerpare, Alyanak, and Hacıhaliloğlu apricot cultivars
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Pearson correlation and Principal Component Analysis (PCA)

In the investigation of the effects of HA and Si on apricot seedlings of various cultivars, a PCA was conducted using data encompassing plant growth parameters, physiological attributes, and leaf mineral contents. The variables collectively observed in the PCA analysis accounted for a cumulative explanation rate of 53.82%. The results revealed a positive impact of HA and Si on the examined parameters, indicating enhanced plant performance. As depicted in Fig. 3a, the control groups clustered in the negative correlation, while the cultivars subjected to HA and Si treatments, both individually and in combination, were clustered on the positive side. Furthermore, the plant growth parameters, physiological measurements, and leaf mineral contents exhibited an overall increase in plants treated with HA and Si, aligning in parallel on the positive side of the plot. Notably, LT decreased in the presence of HA and Si compared to the control groups, resulting in its solitary clustering in the opposite direction to other parameters. Concurrently, Pearson correlation analysis was applied to all parameters investigated in the study, revealing specific associations. In Fig. 3b, a robust negative correlation was evident between LT and shoot fresh and dry weights, as well as weak SC. Additionally, K displayed a weak and negative correlation with RFW, RDW, RL, P, and LT. Conversely, positive correlations were observed among various parameters, including RFW, RDW, SFW, SDW, TPFW, TPDW, Chl, SL, RL, SD, LA, N, P, Ca, and Mg values.

Fig. 3
figure 3

Presents the loading plot of all measured variables incorporated in Principal Component Analysis (PCA) for morphological, physiological, and mineral traits (a). The loading plot visually represents the contribution of each variable to the principal components. Additionally, Pearson’s correlation between all traits is depicted in (b), where correlation coefficients are color-coded: red indicates a positive correlation ranging from 0 to 1, and blue indicates a negative correlation ranging from 0 to −1. The abbreviations corresponding to the variables are as follows: LA Leaf Area, TLN Total Leaf Number, SD Shoot Diameter, SL Shoot Length, RL Root Length, RFW Root Fresh Weight, SFW Shoot Fresh Weight, TPFW Total Plant Fresh Weight, RDW Root Dry Weight, SDW Shoot Dry Weight, TPDW Total Plant Dry Weight, LT Leaf Temperature, Chl Chlorophyll Content, SC Stomatal Conductance, Ca Leaf Calcium Content, K Leaf Potassium Content, N Leaf Nitrogen Content, Mg Leaf Magnesium Content, P Leaf Phosphorus Content

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Discussion

Our findings provided valuable insights into the effects of HA, Si and HA + Si applications on various physiological and morphological parameters in apricot seedlings, as depicted in Fig. 1a–g. Regarding SC, the significant increase in stomatal conductance observed in the HA and SI treatments, especially in the combined HA + Si treatment, aligns with existing literature emphasizing the positive impact of HA on stomatal conductance (Mustafa et al. 2021). This improvement in SC is crucial for efficient gas exchange and enhanced photosynthetic rates. SC was also significantly influenced by the application of HA and Si, particularly when used in combination, as shown by the highest SC values in the HA + Si treatment. While SC was significantly influenced by the treatments, CI remained unaffected. This discrepancy suggests that despite the positive impact on stomatal conductance, HA and Si may not have a direct effect on chlorophyll fluorescence. This aligns with studies emphasizing the multifaceted nature of plant responses to these treatments (Waqas et al. 2012). Considering CI, the elevated chlorophyll concentrations in the Şekerpare HA + Si and Alyanak Si applications indicate a positive role of these treatments in enhancing photosynthetic pigments. Similar findings have been reported in previous studies highlighting the positive influence of silicon on chlorophyll content (Liang et al. 2015). Besides, the absence of significant differences in CI across all treatments suggests that factors other than chlorophyll content may be responsible for any observed differences in seedling growth or health. HA treatment did not result in a statistically significant increase in CI compared to the control, as indicated by the shared letter, suggesting that HA does not substantially affect chlorophyll content. Si treatment similarly shows no significant difference from the control in terms of CI, which is consistent with the results from HA treatment. The HA + Si treatment does not significantly improve CI over the control, HA, or Si treatments, as indicated by the shared letter across all treatments, suggesting that neither individual nor combined treatments have a significant impact on chlorophyll content. Stomatal conductance was significantly influenced by the application of HA and Si, particularly when used in combination, as shown by the highest SC values in the HA + Si treatment. In contrast, the chlorophyll index was not significantly affected by any of the treatments, indicating that the treatments did not alter the chlorophyll content in a statistically meaningful way. On the other hand, the reduction in leaf temperature following HA and Si applications suggests a potential role in alleviating heat stress in apricot seedlings. This aligns with studies demonstrating the heat stress ameliorating effects of HA and Si in various crops (SLdi et al. 2021). In our results, the substantial increase in LA and TLN in the HA + Si treatment group indicates a synergistic effect of combined HA and Si applications. This synergism is consistent with findings in other crops, demonstrating enhanced growth parameters with combined applications (Canellas et al. 2015; Hamdia et al. 2004). Across both parameters (LA and TLN) in our findings, the combination treatment (HA + Si) consistently showed the most significant improvement, highlighting the benefits of treatment interaction. HA appears to be more effective than Si when used alone, both in terms of promoting leaf area and increasing TLN. The incremental benefits of adding Si to HA suggest that while Si’s contributions are beneficial, they are maximized when combined with HA. These findings suggest that the application of HA, either alone or in combination with Si, could be a potent strategy for enhancing seedling growth and TLN. The data also indicated the potential for additive or synergistic effects when combining different treatment types.

The control seedlings presented a baseline SL, which was comparatively lower than the treatment groups. HA treatment showed an increase in SL, though not the highest, indicating its positive effect on root development. Si treatment appears to have a similar impact on SL as HA, without any significant difference between them, suggesting that Si alone can also promote root growth to a comparable degree. The HA + Si treatment group exhibited no significant increase over HA or Si alone, implying that the combination does not enhance SL beyond the effect of individual treatments. The lack of significant difference in SL among treatments suggests that while both HA and Si contribute positively to shoot length, their combined effect might not surpass individual treatments. In contrast, SL significantly increased in the HA + Si treatment, implying a specific synergy in promoting the net assimilation rate. The SL in the control seedling was the lowest, serving as a reference point. HA treatment led to a moderate increase in SL, suggesting improved photosynthetic efficiency or growth rate per unit leaf area. Si treatment did not significantly increase SL over the control, indicating that its impact on photosynthetic efficiency might be limited. The combination of HA and Si showed a significant increase in SL compared to the control, HA alone, and Si alone, suggesting that the treatments in combination have a synergistic effect on photosynthesis and growth rate. SL did not show a clear synergistic effect from HA and Si combined, as all treatments resulted in similar outcomes, which were nonetheless better than the control. SL, on the other hand, was significantly improved by the combination of HA and Si, indicating that for parameters related to assimilation and growth efficiency, the combination treatment is superior. The data suggest that while HA and Si individually contribute to root growth, their combination is particularly beneficial for enhancing the net assimilation rate. Such interaction effects have been reported in the literature, emphasizing the complexity of interactions in combined treatments (Colla et al. 2014). The control seedling displayed the lowest RL, establishing the baseline measurement for comparison against treated groups. HA treatment resulted in a significant improvement in RL over the control, denoting its beneficial effect on root elongation. Si treatment did not significantly improve RL over the control, suggesting that silicon may not independently enhance root length relative to untreated plants. The combined HA + Si treatment showed a slight improvement in RL compared to HA alone, though this was not as pronounced as the difference between HA and control. However, when combined with HA, Si may contribute to a marginal increase in RL, though further statistical analysis would be required to determine the significance of this observation. In conclusion, HA is confirmed to be effective in promoting root elongation as evidenced by increased RL. The data indicates a potential synergistic or additive effect of HA and Si on root growth, although the impact of combined treatments on RL is less pronounced than on other growth parameters discussed previously. In general, the significant improvement in RL in the HA treatment aligns with studies showcasing the positive impact of humic substances on root development and elongation (Zandonadi et al., 2007). The marginal increase in RL with combined HA + Si treatment suggests a potential complementary effect, although it’s less pronounced than the impact of HA alone.

The treatments exhibited significant influences on the diverse growth parameters of the apricot cultivars under scrutiny. The application of HA resulted in a substantial increase in SFW at 60.53 g, highlighting its efficacy in promoting shoot biomass. This finding aligns with previous studies that have emphasized the positive impact of humic acid on plant growth (Bolat et al. 2022). Notably, Alyanak stood out among all cultivars, displaying the highest SFW at 62.60 g, indicating variety-specific responses (Dogan et al. 2022). Similarly, Alyanak exhibited the highest RFW at 30.07 g, while Hacıhaliloğlu displayed the lowest at 14.08 g. This indicates the variety-specific nature of the responses to treatments, confirming that different apricot cultivars may react differently to the applied treatments (Korkmaz et al. 2023). The application of HA also led to the highest TPFW at 85.78 g, significantly surpassing the control and other treatments. Alyanak once again demonstrated the highest TPFW at 92.67 g, indicating its favorable response to the treatments (Table 1). This aligns with previous research highlighting the growth-promoting effects of humic acid (Korkmaz et al. 2022). The SDW, Alyanak exhibited the highest values at 23.79 g, and HA treatment resulted in the highest SDW at 24.56 g, emphasizing the positive impact of HA on shoot dry weight (Dogan et al. 2022). Consistently, Alyanak and HA treatment exhibited the highest RDW values at 7.60 and 7.25 g, respectively, reinforcing the effectiveness of HA in promoting root dry biomass (Dogan et al. 2022). Trends in TPDW mirrored those observed in SDW and RDW, with Alyanak and HA treatment recording the highest values. This reaffirms the positive impact of HA on overall plant dry weight (Korkmaz et al. 2022). Interestingly, the interaction between treatments and cultivars did not yield statistically significant differences, suggesting that the individual effects of treatments and cultivars were more pronounced than any combined effects (Kaya et al. 2006). On the other hand, our results indicated substantial disparities in these mineral levels, and N and P content were significantly impacted by both treatment types (T) (p < 0.0001) and Cultivar (V) (p < 0.0001). In the context of N content, the HA treatment emerged with the highest mean value at 2.36%, closely followed by Si at 2.13%, and the combined HA + Si treatment at 2.12%. Among the cultivars, Alyanak exhibited the highest nitrogen content (2.21%), while Hacıhaliloğlu had the lowest (2.11%). These findings align with earlier studies that emphasized the positive impact of humic substances on nitrogen metabolism in plants (Canellas et al. 2019). Concerning P content, Alyanak stood out with the highest value among cultivars at 0.38%, and the HA treatment demonstrated the highest P content at 0.37%, followed closely by Si (0.36%) and HA + Si (0.33%). Previous research has highlighted the role of humic acid in enhancing phosphorus availability and uptake in plants (SLdi et al. 2021; Trevisan et al. 2010). K content exhibited significant differences in response to treatment types (T) (p < 0.0001), with the Si treatment showing the highest K content at 4.10%, followed by HA + Si (4.26%) and HA (3.98%). Interestingly, cultivars did not exhibit significant differences in K content. Previous studies have suggested the influence of silicon on potassium content and uptake in various plant species (Ma and Yamaji 2006; Liang et al. 2015). Moreover, Mg and Ca content displayed significant variations in response to both treatment types (T) (p < 0.0001) and cultivars (V) (p < 0.0001). The highest Mg content was observed in Alyanak (0.37%), and the lowest in Şekerpare (0.31%). Si and HA + Si treatments demonstrated the highest Mg content (0.39 and 0.33%, respectively). Similarly, the highest Ca content was observed in Alyanak (1.35%), while the lowest was in Hacıhaliloğlu (1.08%). The HA treatment exhibited the highest Ca content at 1.30%, followed by Si (1.29%) and HA + Si (1.11%). The interaction between treatments and cultivars (T*V) was significant for Ca content (p = 0.01293), indicating a complex interplay between different treatments and apricot cultivars (Table 2). On the other hand, the variables collectively considered in the PCA analysis accounted for a cumulative explanation rate of 53.82%. The outcomes of the analysis unveiled a positive influence of both HA and Si on the examined parameters, signifying an overall improvement in plant performance. As illustrated in Fig. 3a, the control groups exhibited clustering in the negative correlation region, while the cultivars subjected to HA and Si treatments, whether individually or in combination, were clustered on the positive side. Furthermore, plant growth parameters, physiological measurements, and leaf mineral contents demonstrated a general increase in plants treated with HA and Si, aligning in parallel on the positive side of the plot. Notably, LT exhibited a decrease in the presence of HA and Si compared to the control groups, leading to its distinct clustering in the opposite direction to other parameters. Concurrently, PCA was applied to all parameters investigated in the study, uncovering specific associations. In Fig. 3b, a robust negative correlation was evident between LT and shoot fresh and dry weights, as well as weak SC. Additionally, K displayed a weak and negative correlation with RFW, RDW, RL, P, and LT. Conversely, positive correlations were observed among various parameters, including RFW, RDW, SFW, SDW, TPFW, TPDW, Chl, SL, RL, SD, LA, N, P, Ca, and Mg values.

Conclusions

Comprehensive investigation into the physiological and growth parameters of apricot seedlings subjected to different treatments HA, Si, and their combination has yielded valuable insights into the intricacies of plant responses. The research findings showcased significant differences in stomatal conductance, chlorophyll content, leaf temperatures, and diverse growth parameters among distinct apricot cultivars. A notable highlight was the consistent and substantial enhancement observed in multiple aspects with the combined application of HA + Si, outperforming individual treatments and control seedlings. Graphical representations effectively illustrated the positive influence of HA and Si applications on crucial growth parameters, indicating their promising role in improving overall plant growth. The synergistic effects seen in the combined HA + Si treatment hinted at a complementary influence, underscoring the significance of treatment interactions in shaping plant physiological responses. The leaf mineral analysis brought attention to noteworthy fluctuations in N, P, K, Mg, and Ca concentrations, suggesting an impact of treatments on nutrient assimilation. The PCA findings further affirmed the positive outcomes of HA and Si on overall plant performance, reinforcing the potential of these treatments in fostering sustainable agricultural practices. In summary, this study contributes valuable insights into tailoring agricultural practices for optimizing apricot crop growth. The findings indicate the effectiveness of HA and Si treatments, particularly in combination, showcasing their potential to enhance physiological responses and nutrient uptake. These insights may be crucial for advancing sustainable farming practices in apricot cultivation.