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Article

Threshold Effects of Nitrogen Fertilization Rates on Growth and Essential Oil Yield with Component Regulation in Cinnamomum camphora var. linaloolifera

by
Zhirong Liu
1,†,
Xinyi Chen
1,†,
Jiao Zhao
1,
Luyuan Sun
1,
Jian Guo
1,
Yangyang Shao
1,
Jia Liu
2,
Lei Zhong
3,
Haiyan Zhang
1,
Yanbo Wang
1 and
Jie Zhang
1,*
1
Jiangxi Provincial Engineering Research Center for Seed-Breeding and Utilization of Camphor Trees, School of Soil and Water Conservation, Nanchang Institute of Technology, Nanchang 330200, China
2
Institute of Soil and Fertilizer & Resource and Environment, Jiangxi Academy of Agricultural Sciences, Nanchang 330200, China
3
School of Earth System Science, Tianjin University, Tianjin 300072, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2025, 15(6), 1387; https://doi.org/10.3390/agronomy15061387
Submission received: 9 May 2025 / Revised: 30 May 2025 / Accepted: 3 June 2025 / Published: 5 June 2025
(This article belongs to the Section Soil and Plant Nutrition)
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Abstract

:
The determination of an optimal nitrogen (N) fertilization rate is critical for the sustainable large-scale cultivation of Cinnamomum camphora var. linaloolifera for essential oil production. Both suboptimal and excessive nitrogen inputs can adversely affect plant sustainable development and essential oil biosynthesis, underscoring the necessity of precise nutrient management. This study investigated the effects of five N application rates (0, 45, 90, 135, and 180 kg·hm−2) on vegetative growth, essential oil yield, and quality. Growth parameters, including plant height, basal diameter, specific leaf area (SLA), and essential oil yield and yield rate. Oil composition was characterized via gas chromatography–mass spectrometry (GC-MS). The application of 90 kg·hm−2 N significantly enhanced plant height (74.31%), basal diameter (54.95%), SLA (20.91%), and biomass (181.8%) relative to the nitrogen-free control. Nitrogen uptake was concentrated in foliar tissues, accounting for 82.8% of total plant nitrogen accumulation. This fertilization rate also maximized essential oil yield (9.15 g·plant−1) and yield rate (2.44%), reflecting increases of 178.9% and 24.49%, respectively. Linalool was the predominant oil constituent (89.84–91.81%), with its highest concentration observed at the 90 kg·hm−2 treatment. At this rate, the relative abundance of oxygenated compounds increased by 0.97%, while hydrocarbon content decreased by 0.62%, indicating a qualitative improvement in oil composition. The findings reveal a threshold response to nitrogen input, wherein rates exceeding 90 kg·hm−2 did not confer further benefits and may reduce efficiency. Collectively, these results suggest that a nitrogen application rate of 90 kg·hm−2 optimally enhances vegetative growth, nitrogen assimilation, and both the quantitative and qualitative traits of essential oils in C. camphora var. linaloolifera.

1. Introduction

Cinnamomum camphora, a subtropical evergreen broad-leaved species of the Lauraceae family, is classified as a Class II protected plant in China. It is naturally distributed across the southern regions of China (including Taiwan), parts of the Southeast Asian Peninsula (e.g., Vietnam, Laos, and Cambodia), and Japan, with successful introductions into eastern Australia’s Gold Coast and the southern United States. Jiangxi Province, China, represents a major center of diversity for this species and is often referred to as the “Hometown of Camphor” due to its abundance and varietal richness [1,2,3]. As a native aromatic and ornamental tree with considerable ecological and economic value, C. camphora is utilized for the extraction of camphor and camphor oil from its roots, stems, and leaves. These essential oils have broad applications in the industrial and pharmaceutical sectors, positioning C. camphora as a promising candidate for selective breeding and value-added utilization. Based on the dominant constituents of its essential oil components, the species can be classified into different chemotypes. Among these, the linalool-type variant (C. camphora var. linaloolifera) is particularly valued for its high linalool concentration [4]. Essential oil content is markedly higher in leaves than in branches, making foliage the preferred raw material for essential oil extraction [5]. Traditional harvesting practices typically involve whole-tree felling, a method that is ecologically unsustainable. In contrast, recent advancements have introduced a low-canopy cultivation model that allows for the periodic harvesting of aerial shoots while preserving the basal structure. This regenerative approach supports rapid sprout development, shortens the harvesting cycle, reduces input costs, and enhances overall yield [6,7]. Therefore, C. camphora var. linaloolifera grown under low-canopy systems offers a renewable source of essential oils, aligning with industrial demands for sustainable, natural linalool production [8].
Plant nutrient availability plays a fundamental role in supporting both vegetative growth and secondary metabolism. Trees absorb nutrients from the soil through their root systems, with increasing demands during periods of rapid growth [9,10]. Nitrogen (N), phosphorus (P), and potassium (K) are primary macronutrients for tree growth in appropriate proportions. Nitrogen, a constituent element of plant cell protoplasm and proteins, plays a vital role in vegetative growth. Adequate nitrogen supply promotes plant cell growth and division, enhances photosynthetic rates, and consequently stimulates tree growth [11]. As an indispensable element in agricultural production, nitrogen fertilizer plays a crucial role in promoting plant growth and increasing crop yields [12,13,14,15]. For many economic tree species, appropriate nitrogen application not only stimulates growth but also profoundly affects the yield and quality of secondary metabolites [16,17].
Focusing specifically on nitrogen fertilization, Alizadeh et al. [18] found that nitrogen application significantly increased essential oil composition, total phenol content, and antioxidant activity in Satureja hortensis L. Likewise, Sifola et al. [19] discovered that nitrogen fertilization effectively increased the concentration and relative abundance of leaf essential oil components in Ocimum basilicum L.
However, the benefits of nitrogen fertilization are contingent upon the application rate. Excessive nitrogen inputs can disrupt nutrient homeostasis, inhibit physiological function, and compromise the biosynthesis of valuable secondary metabolites—a trade-off particularly evident in the intensive cultivation of aromatic plants [20]. While considerable research has explored nitrogen’s role in herbaceous species (such as mint and basil), studies on woody aromatic taxa such as C. camphora remain scarce. Preliminary findings suggest that moderate nitrogen fertilization enhances vegetative parameters such as plant height, basal diameter, and leaf area, whereas excessive application may inhibit physiological activity [21]. Additionally, the mechanisms through which nitrogen modulates essential oil composition, particularly the ratio of oxygenated to hydrocarbon constituents, remain inadequately understood. Therefore, elucidating the physiological responses of C. camphora var. linaloolifera to different nitrogen levels can provide theoretical guidance for precise nitrogen application and cultivation management optimization. Identifying the nitrogen fertilization rate that optimally balances biomass accumulation with essential oil yield and quality of C. camphora var. linaloolifera will inform more efficient and sustainable cultivation practices for this economically valuable species.

2. Materials and Methods

2.1. Experimental Site and Conditions

The experiment was conducted in the High-Tech Development Zone of Nanchang City, Jiangxi Province, China, characterized by a subtropical humid climate. The average annual temperature in the region is 19.0 °C, with total annual precipitation of 1518 mm and an average annual sunshine duration of 1775 h. The frost-free period lasts for 259 d. From April to October 2021, the highest temperature in the region was 35 °C, the lowest temperature was 18 °C, the average temperature was 25 °C, and the average rainfall was 165 mm. The soil at the experimental site is classified as red soil (Ultisols and Oxisols in US Soil Taxonomy System), derived from Quaternary red clay parent material. The physicochemical properties of the surface soil (0–20 cm depth) are as follows: pH 5.47, organic matter 6.39 g·kg−1, total nitrogen 0.62 g·kg−1, total phosphorus 0.30 g·kg−1, total potassium 13.00 g·kg−1, alkali-hydrolyzable nitrogen 47.74 mg·kg−1, available phosphorus 1.49 mg·kg−1, available potassium 61.10 mg·kg−1, and cation exchange capacity 5.81 cmol·kg−1 [22].

2.2. Experimental Materials

The C. camphora cuttings used in this study were sourced from the C. camphora germplasm resource protection and breeding base in Jinxi, Jiangxi Province, China. Uniform, healthy cuttings of the clonal variety “Ganfang No. 1” were selected for the experiment. The average length of the cuttings was approximately 15 cm.

2.3. Experimental Design

The experiment was performed according to local agronomic practices. The trees were planted on 10 April 2021 at a spacing of 1.0 m × 1.0 m, resulting in a planting density of 10,000 trees per hectare. Three replicates were established for each treatment, with each replicate occupying a 3.0 m × 3.0 m plot containing nine trees. The experimental design included five nitrogen fertilization treatments: N0 (control), N45, N90, N135, and N180 kg·hm−2. Fertilizer application was conducted on 20 April 2021, as outlined in Table 1. Fertilization was performed using urea (46% N) as the nitrogen source, calcium-magnesium phosphate (12% P2O5) as the phosphorus source, and potassium chloride (60% K2O) as the potassium source. The application rates for phosphorus and potassium are both 90 kg·hm−2 [23]. A ring-shaped trench (approximately 25 cm from the center of the tree) was dug to a depth of 20 cm for the fertilizer application, which was then backfilled with soil.

2.4. Sample Measurements

2.4.1. Plant Height, Basal Diameter, and Leaf Area Measurement

Measurements were taken from September to October 2021. Plant height was measured from the soil surface to the base of the terminal bud using a tape measure. The basal diameter was measured at the soil line in two perpendicular directions using a digital vernier caliper, and the average of the two measurements was recorded as the basal diameter [24]. For leaf area determination, thirty mature, healthy leaves were randomly selected from each tree and measured using a leaf area meter. The specific leaf area (SLA, cm2·g−1) was calculated by dividing the total leaf area (cm2) by the total leaf biomass (g) [25].

2.4.2. Biomass and Nutrient Content Measurement

The experiment adopted a low-canopy cultivation model. Above-ground biomass was harvested by cutting the trees at ground level. The fresh weight of branches and leaves was recorded immediately after harvesting. Remove the leaves needed for essential oil extraction from all the leaves, and the remaining plant material was blanched at 105 °C for 30 min, followed by drying at 80 °C until a constant weight was achieved to determine water content and biomass. After drying, the branches and leaves separately were ground through a 2 mm sieve for further analysis. The nitrogen content in the plant material was quantified using the semi-micro Kjeldahl method [26].

2.4.3. Essential Oil Extraction and Component Analysis

For essential oil extraction, 300 g of leaves from each tree were subjected to steam distillation. The yield of essential oil was calculated as the mass of oil extracted divided by the leaf biomass, expressed as a percentage [27]. Additionally, essential oil yield (kg·hm−2) was calculated for each treatment. The chemical composition of the essential oils was analyzed using GC-MS with an Agilent 7890B-5977A system (Agilent Technologies Inc., Santa Clara, CA, USA), equipped with an HP-5MS capillary column. Helium was used as the carrier gas at a flow rate of 1.0 mL/min. The injection port was set to 250 °C, with a split ratio of 10:1, and the injection volume was 1.0 µL. The temperature program began at 50 °C (held for 2 min), then increased at a rate of 10 °C/min to 250 °C, where it was held for 10 min. The mass spectrometer (Agilent Technologies Inc., Santa Clara, CA, USA) was operated in electron ionization mode (EI, 70 eV), with the ion source temperature set to 230 °C and the interface temperature set to 280 °C. The scan range was m/z 50–500. Compound identification was performed by comparing the mass spectra with the NIST11 library using retention times and mass spectral fragmentation patterns. The relative abundance of each compound was determined using the area normalization method [28].

2.5. Data Processing and Statistical Analysis

After GC-MS analysis, essential oil compounds were identified by matching their mass spectra with those in the NIST11 library [29]. A table was created based on retention times. Data were processed using Microsoft Excel 2010. Statistical analyses were performed using SPSS 20.0 software, with one-way analysis of variance (ANOVA) followed by Duncan’s multiple range test. Graphical representations of the data were generated using OriginPro 2024 software.

3. Results

3.1. Effects of Nitrogen Fertilization on Plant Height, Basal Diameter, SLA, and Biomass

The effects of different nitrogen fertilization rates on plant height, basal diameter, and SLA in C. camphora var. linaloolifera are presented in Figure 1. Nitrogen application resulted in increased plant height and basal diameter, but excessive nitrogen had an inhibitory effect on growth. Across the nitrogen application rates from 0 to 90 kg·hm−2, all measured growth parameters exhibited positive responses, with increases in these traits corresponding to higher nitrogen levels. Specifically, the N90 treatment yielded the highest values for plant height (1.21 m), basal diameter (6.88 cm), and SLA, showing increases of 74.31% and 20.91%, respectively, compared to the N0 (control) treatment. However, nitrogen levels exceeding 90 kg·hm−2 (N135 and N180) led to a decrease in plant height, basal diameter, and SLA. At N180, these parameters were reduced by 34.71% and 11.63%, respectively, compared to the N90 treatment. Overall, nitrogen fertilization significantly increased these growth parameters (p < 0.05), with increases ranging from 11.78% to 74.39% across the treatments.
Nitrogen fertilization significantly enhanced the biomass of C. camphora var. linaloolifera (Figure 2). As nitrogen fertilization rates increased, the total biomass, leaf biomass, and branch biomass initially increased, peaking at the N90 treatment, and then declined with further increases in nitrogen levels. The N90 treatment yielded the highest values for both total and organ-specific biomass, with total biomass and branch biomass reaching 0.770, 0.425, and 0.320 kg·plant−1, respectively. Compared to the N0 treatment, these values represented increases of 182.1%, 174.2%, and 183.2%, respectively. However, when nitrogen application exceeded 90 kg·hm−2, further fertilization led to decreased biomass. In the N180 treatment, total biomass, leaf biomass, and branch biomass were reduced by 32.34%, 31.29%, and 37.81%, respectively, compared to those in the N90 treatment.

3.2. Nitrogen Accumulation in C. camphora var. linaloolifera

Nitrogen fertilization significantly influenced nitrogen accumulation in C. camphora var. linaloolifera (Figure 3). As nitrogen application rates increased, nitrogen accumulation in the whole plant, as well as in the leaves and branches, exhibited a consistent upward trend. In the N180 treatment, total nitrogen accumulation in the plant, along with nitrogen in the leaves and branches, reached 7.888, 6.538, and 1.350 g·kg−1, respectively, representing increases of 172.58%, 175.41%, and 173.06% compared to the control (N0). Of this total, the net nitrogen accumulation in the leaves was 4.139 g·kg−1, while it was substantially lower at 0.860 g·kg−1 in the branches.

3.3. Effects of Nitrogen Fertilization on Essential Oil Yield and Yield Rate

The relationship between nitrogen fertilization rates and essential oil yield and yield rate is shown in Figure 4. Both essential oil yield and yield rate exhibited an initial increase, followed by a decrease as nitrogen application rates increased. The highest essential oil yield (9.15 g·plant−1) and yield rate (2.44%) were recorded at the N90 treatment, representing increases of 178.9% and 24.49%, respectively, relative to the N0 treatment (p < 0.05). While nitrogen application at rates between 90 and 180 kg·hm−2 led to a decrease in both essential oil yield and yield rate, the N135 and N180 treatments still showed moderate increases in oil yield and yield rate, ranging from 12.76% to 112.5%, compared to the control treatment.

3.4. Influence of Growth Parameters on Essential Oil Yield and Yield Rate

As illustrated in Figure 5, increases in plant height, basal diameter, and SLA were significantly correlated with higher essential oil yield and yield rate (p < 0.01). Among these growth parameters, SLA had the strongest correlation with essential oil yield, as evidenced by a high R2 value (R2 = 0.58861). Previous results demonstrated that nitrogen fertilization significantly enhanced plant height, basal diameter, and SLA, with the N90 treatment producing the highest values for these parameters. Consequently, plants exhibiting larger growth parameters (height, basal diameter, and SLA) also displayed higher essential oil yields and yield rates. For instance, a plant with a height of 1.27 m and an SLA of 6.88 cm2·g−1 produced 7.28 g of essential oil, corresponding to a yield rate of 2.46%.

3.5. Volatile Components of Essential Oil

GC-MS analysis identified a total of 90 volatile compounds in the essential oil of C. camphora var. linaloolifera leaves. Specifically, 86 volatile compounds were detected in the N0 treatment, 87 in the N45 treatment, 84 in the N90 treatment, and 87 in the N180 treatment.
The major components identified included linalool, citral, and α-guaiacene. As shown in Figure 6, linalool was the dominant component in all treatments, with the highest concentration observed in the N90 treatment (92.114 ± 0.215%). However, its relative abundance slightly decreased as nitrogen application rates increased (90.5 to 90.7%). Conversely, humulene showed a dose-dependent increase in relative abundance (1.229 to 2.118%). Among the other major components, citronellal decreased with higher nitrogen levels, while α-santalene remained relatively stable, showing minimal response to nitrogen fertilization (Appendix A).
As shown in Figure 7, compared to the N0 treatment, nitrogen fertilization increased the relative abundance of alcohols and aldehydes while reducing the relative abundance of hydrocarbons, ketones, and esters. The number of alcohols increased by 2, 2, 4, and 8 compounds in the N45, N90, N135, and N180 treatments, respectively.
Figure 8 shows the effects of nitrogen fertilization on the relative abundance of different volatile compounds in the essential oil. Compared to the N0 treatment, the N45 and N135 treatments increased the relative abundance of alcohols and ketones while decreasing the relative abundance of hydrocarbons, aldehydes, and esters. A similar pattern was observed under the N90 and N180 treatments. Across all treatments, alcohols were the predominant class of volatile compounds, with relative abundances ranging from 93.19% to 94.02%. Compared to the N0 treatment, the increase in alcohol content across treatments ranged from 0.48% to 0.97%. Hydrocarbons were the second most abundant class, with relative abundances between 4.72% and 5.27%, showing a reduction of 0.25% to 0.62% compared to the N0 treatment. Additionally, the relative abundance of oxygenated compounds in the N0, N45, N90, N135, and N180 treatments was 94.73%, 95.07%, 95.35%, 95.29%, and 94.98%, respectively. Nitrogen fertilization increased the content of oxygenated compounds while reducing hydrocarbon content in the leaf essential oil, with N90 treatment showing the most favorable effects.

3.6. Effects of Growth Parameters on Essential Oil Composition

As shown in Figure 9, increased plant height and SLA resulted in a higher relative abundance of linalool and a decrease in the relative abundance of hydrocarbons in the essential oil of C. camphora var. linaloolifera leaves. This trend was particularly evident in the N90 treatment, which produced the highest growth parameters, the highest relative abundance of linalool (above 91%), and the lowest relative abundance of hydrocarbons (below 4.5%).

4. Discussion

4.1. Effects of Nitrogen Fertilization on Growth and Physiological Traits of C. camphora var. linaloolifera

Seedling height, biomass, and nutrient content are critical indicators of plant growth and development. Monitoring these parameters enables systematic investigation of nutrient uptake dynamics, facilitating the identification of plant nutritional requirements and guiding the formulation of optimal fertilization strategies. These strategies ultimately contribute to the synergistic enhancement of both yield and the quality of target products [30]. During the vigorous growth phase, C. camphora var. linaloolifera experiences high nutrient demands. Appropriate fertilizer application can provide adequate mineral nutrition for growth, promoting branch and leaf differentiation and increasing biomass and nutrient content [31]. Dong et al. [32] studied the growth of Phoebe chekiangensis under nitrogen, phosphorus, and potassium fertilization, finding that nitrogen had the most significant impact on its growth and development. Nitrogen plays a pivotal role in protein, chlorophyll, and nucleic acid synthesis, all of which are essential for cellular division, expansion, and photosynthesis, thereby accelerating plant growth [33]. However, when nitrogen application exceeds 90 kg·hm−2 (as seen in N135 and N180 treatments), a significant decline in growth parameters and biomass was observed. This “increase-then-decrease” response suggests the presence of a threshold effect in the growth of C. camphora var. linaloolifera with respect to nitrogen fertilization. Excessive nitrogen may lead to the accumulation of soil salts or ionic imbalances, which inhibit the root system’s capacity to absorb water and other nutrients, inducing physiological stress [34]. Additionally, Ibrahim et al. [35] found that high nitrogen environments may direct more resources to vegetative growth, often at the expense of secondary metabolite production. This aligns with our findings, where excessive nitrogen reduced essential oil yield and yield rate. Similar findings were reported by Jankowski, K.J. et al. [36], who observed that medium nitrogen levels optimized growth in Helianthus tuberosus L., while high nitrogen levels suppressed its development. This study supports the fact that within a specific range, nitrogen fertilization stimulates growth and development, but excessive nitrogen disrupts the plant’s water and nutrient balance, limiting its overall growth potential [37]. Research has shown that wheat height, leaf area, and biomass initially increase and then decrease with rising nitrogen concentrations [38]. Our results corroborate these findings, with nitrogen fertilization between 0 and 90 kg·hm−2 leading to improvements in plant height, basal diameter, SLA, and biomass. Compared to the N0 treatment, the N90 treatment showed the most significant increases: 74.39% in plant height, 54.95% in basal diameter, 20.93% in SLA, and 181.8% in biomass. Furthermore, nitrogen accumulation in the plant tissues with higher nitrogen fertilization rates. In the N180 treatment, total nitrogen accumulation reached 7.888 g·kg−1, a 172.6% increase compared to the control. Leaf nitrogen net accumulation was 4.139 g·kg−1, while branch nitrogen net accumulation was only 0.860 g·kg−1. However, the biomass production efficiency decreased which could be attributed to dilution effects or metabolic imbalances resulting from excessive nitrogen [39].

4.2. Effects of Nitrogen Fertilization on Essential Oil Yield and Quality of C. camphora var. linaloolifera

Essential oils, as secondary metabolites of aromatic plants, are intrinsically linked to plant growth and soil nutrient status [40]. This study demonstrates that nitrogen fertilization significantly influences essential oil yield, yield rate, and quality by improving growth parameters such as plant height, basal diameter, and SLA. These growth improvements enhance photosynthesis, a critical process through which plants convert light energy into chemical energy, thereby synthesizing various organic compounds, including essential oil precursors. A larger SLA enhances the photosynthetic capacity, directly contributing to the synthesis of secondary metabolites, including essential oils. Adequate supplies of nitrogen, phosphorus, and potassium promote plant growth and metabolic activity, which in turn boosts essential oil synthesis. Plants with greater height, basal diameter, and SLA typically possess more extensive root systems, improving their nutrient absorption capabilities. Essential oil synthesis and accumulation are closely linked to plant growth conditions, and increases in height, basal diameter, and SLA typically indicate enhanced plant vigor, enabling greater accumulation of secondary metabolites [41]. In this study, nitrogen fertilization significantly improved these key growth parameters, thereby strengthening photosynthesis, nutrient absorption, utilization efficiency, and secondary metabolite accumulation. These improvements collectively contributed to a substantial increase in leaf essential oil yield, yield rate, and quality. Ehsanipour et al. [20] found that appropriate nitrogen fertilization can increase fennel essential oil yield, but excessive nitrogen application leads to declining productivity. Consistent with these findings, the present study revealed that essential oil yield and yield rate in C. camphora var. linaloolifera responded positively to increasing nitrogen levels. Compared to the N0 treatment, the N90 treatment showed the best improvement, increasing essential oil yield by 5.87 g·plant−1 and the yield rate by 0.48%.
GC-MS analysis revealed that linalool was the predominant oxygenated compound in the essential oil, with the highest relative abundance found in the N90 treatment (91.81%), indicating that this nitrogen level also optimized the oil’s quality. The essential oil contained a variety of compounds, including alcohols, hydrocarbons, aldehydes, ketones, esters, phenols, and ethers. Alcohols were the most abundant compound class, making up between 93.19% and 94.02% of the oil, followed by hydrocarbons, which accounted for 4.72% to 5.35%. Nitrogen fertilization, especially at the N90 rate, significantly increased the relative abundance of oxygenated compounds (such as linalool and α-farnesene), with a maximum increase of 0.97%, while hydrocarbons decreased by as much as 0.62%. These shifts are crucial for improving oil quality, as oxygenated compounds are typically associated with higher bioactivity and economic value [42]. The decrease in hydrocarbons, coupled with the increase in oxygenated compounds, further suggests that nitrogen fertilization helps regulate key components in essential oils, enhancing both yield and quality [43]. In conclusion, nitrogen fertilization increased linalool content while decreasing hydrocarbon content to varying degrees. Therefore, studying the effects of nitrogen fertilization on the yield, yield rate, and composition of C. camphora var. linaloolifera essential oil helps regulate key component content, providing a theoretical basis and technical support for the development of the essential oil industry.

5. Conclusions

This study systematically assessed the effects of different nitrogen fertilization rates on the growth, development, essential oil yield, and quality of C. camphora var. linaloolifera. The findings demonstrated that optimizing nitrogen application to 90 kg·hm−2 significantly enhanced plant growth, with notable increases in plant height (74.31%), basal diameter (54.94%), and SLA (20.91%). In addition, this fertilization strategy led to a substantial improvement in essential oil yield (9.15 g·plant−1) and yield rate (2.44%), representing increases of 178.9% and 24.49%, respectively, compared to conventional management practices. Furthermore, the optimal nitrogen level not only boosted the linalool content in the essential oil but also reduced the relative abundance of hydrocarbons, resulting in improved oil quality. These results provide valuable insights for refining traditional fertilization practices and optimizing the sustainable management of the C. camphora var. linaloolifera essential oil industry.

Author Contributions

Z.L. and X.C.: Formal analysis, writing—original draft, and visualization. J.Z. (Jie Zhang) and J.Z. (Jiao Zhao): Conceptualization, methodology, and writing—review and editing. L.S.: Software, investigation, and data curation. Y.S. and J.G.: Formal analysis, investigation, and data curation. H.Z. and Y.W.: Conceptualization, methodology, and supervision. J.L.: Supervision, funding acquisition, and project administration. L.Z.: Conceptualization, validation, and writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the National Natural Science Foundation of China (32060333 and 31660599), the Jiangxi Provincial Science and Technology Program (20204BCJL23046), and the Special Program for Basic Research and Talent Training of Jiangxi Provincial Education Department (GJJ201925).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed at the corresponding authors.

Acknowledgments

We thank the reviewers and editors for their helpful comments regarding the manuscript.

Conflicts of Interest

The authors confirm that there are no financial interests or personal relationships that could have influenced the research presented in this paper.

Appendix A

Table A1. Effects of different nitrogen fertilization rates on the relative abundance of volatile compounds in the essential oil of Cinnamomum camphora var. linaloolifera leaves.
Table A1. Effects of different nitrogen fertilization rates on the relative abundance of volatile compounds in the essential oil of Cinnamomum camphora var. linaloolifera leaves.
Chemical CompoundChemical FormulaRelative Abundance (%)
N0N45N90N135N180
LinaloolC10H18O89.839 ± 1.004 b91.277 ± 1.361 b91.809 ± 0.534 a91.130 ± 1.607 b91.183 ± 0.738 b
α-CitraldehydeC10H16O1.286 ± 0.458 a0.141 ± 0.000 b---
α-GuaiaceneC15H241.229 ± 0.623 b1.665 ± 0.369 ab1.704 ± 0.182 ab2.143 ± 0.645 a2.118 ± 0.285 a
EucalyptolC15H26O0.694 ± 0.200 a0.626 ± 0.055 ab0.528 ± 0.084 bc0.453 ± 0.124 c0.445 ± 0.083 c
CamphorC10H16O0.622 ± 0.011 b0.660 ± 0.043 ab0.632 ± 0.035 b0.675 ± 0.037 a0.690 ± 0.026 a
β-CitraldehydeC10H16O0.600 ± 0.393----
α-SandaleneC15H240.597 ± 0.184 a0.522 ± 0.155 a0.490 ± 0.041 a0.562 ± 0.178 a0.540 ± 0.080 a
CitronellalC10H18O0.566 ± 0.174 a0.372 ± 0.017 b0.355 ± 0.025 b0.338 ± 0.027 b0.321 ± 0.037 b
EucalyptolC15H24O0.458 ± 0.374 a0.174 ± 0.022 b0.146 ± 0.021 b0.132 ± 0.034 b0.132 ± 0.019 b
HumuleneC15H240.407 ± 0.101 a0.461 ± 0.114 a0.466 ± 0.041 a0.526 ± 0.171 a0.514 ± 0.073 a
δ-ElemeneC15H240.285 ± 0.114 b0.351 ± 0.075 ab0.360 ± 0.038 ab0.450 ± 0.134 a0.445 ± 0.059 a
3-SiderophthaleneC10H160.280 ± 0.040 a0.264 ± 0.016 a0.277 ± 0.017 a0.264 ± 0.028 a0.261 ± 0.024 a
cis-GeraniolC10H18O0.275 ± 0.000 a0.167 ± 0.000 b---
D-LimoneneC10H160.244 ± 0.043 b0.273 ± 0.014 a0.283 ± 0.020 a0.279 ± 0.014 a0.286 ± 0.015 a
α-TerpineolC10H18O0.229 ± 0.045 a0.211 ± 0.011 a0.210 ± 0.008 a0.214 ± 0.011 a0.203 ± 0.011 a
6-Celesten-4-olC15H26O0.146 ± 0.008 a0.131 ± 0.000 b-0.113 ± 0.000 c-
CarvoneC10H14O0.143 ± 0.030 a0.102 ± 0.001 b---
β-PineneC10H160.141 ± 0.023 a0.147 ± 0.010 a0.152 ± 0.008 a0.146 ± 0.008 a0.151 ± 0.009 a
β-OcimeneC10H160.137 ± 0.035 b0.157 ± 0.009 ab0.174 ± 0.021 a0.179 ± 0.008 a0.181 ± 0.015 a
(−)-Eudesmus spatulifolius enolC15H24O0.136 ± 0.007 a0.138 ± 0.010 a0.124 ± 0.014 a0.138 ± 0.014 a0.123 ± 0.017 a
cis-Linalool oxideC10H18O20.132 ± 0.017 a0.118 ± 0.006 a0.124 ± 0.008 a0.117 ± 0.012 a0.119 ± 0.013 a
4-TerpineolC10H18O0.132 ± 0.005 a0.126 ± 0.008 b0.123 ± 0.005 b0.126 ± 0.002 b0.121 ± 0.002 b
trans-Linalool oxideC10H18O20.130 ± 0.005 a0.120 ± 0.007 b0.115 ± 0.006 b0.119 ± 0.006 b0.120 ± 0.008 b
β-ElemeneC15H240.123 ± 0.006 a0.128 ± 0.020 a0.125 ± 0.011 a0.141 ± 0.038 a0.142 ± 0.016 a
α-MulleinC15H240.119 ± 0.005 a0.121 ± 0.024 a0.113 ± 0.009 a0.135 ± 0.038 a0.129 ± 0.018 a
LobeliaC10H18O0.116 ± 0.008 a0.113 ± 0.003 a0.107 ± 0.003 ab0.103 ± 0.001 ab0.086 ± 0.042 b
LauryleneC15H26O--0.185 ± 0.000--
OctadecaneC18H38-0.694 ± 0.000---
ElemolC10H16---0.129 ± 0.000 a0.108 ± 0.000 b
Total 99.198 ± 0.723 a98.81 ± 0.851 a98.907 ± 0.537 a98.060 ± 1.013 a97.937 ± 0.529 a
Notes: “-” means not detected. Different letters within the same row indicate significant differences among the treatments (p < 0.05).

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Agronomy 15 01387 g001
Figure 1. Effects of different nitrogen fertilization rates on plant height (a), basal diameter (b), and SLA (c) of Cinnamomum camphora var. linaloolifera. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
Figure 1. Effects of different nitrogen fertilization rates on plant height (a), basal diameter (b), and SLA (c) of Cinnamomum camphora var. linaloolifera. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
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Agronomy 15 01387 g002
Figure 2. Effects of different nitrogen fertilization rates on total biomass (a), leaf biomass (b), and branch biomass (c) of Cinnamomum camphora var. linaloolifera. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
Figure 2. Effects of different nitrogen fertilization rates on total biomass (a), leaf biomass (b), and branch biomass (c) of Cinnamomum camphora var. linaloolifera. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
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Agronomy 15 01387 g003
Figure 3. Effects of different nitrogen fertilization rates on total nitrogen accumulation (a), leaf nitrogen accumulation (b), and branch nitrogen accumulation (c) in Cinnamomum camphora var. linaloolifera. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
Figure 3. Effects of different nitrogen fertilization rates on total nitrogen accumulation (a), leaf nitrogen accumulation (b), and branch nitrogen accumulation (c) in Cinnamomum camphora var. linaloolifera. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
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Figure 4. Effects of nitrogen fertilization on essential oil yield (a) and yield rate (b) of Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
Figure 4. Effects of nitrogen fertilization on essential oil yield (a) and yield rate (b) of Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
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Agronomy 15 01387 g005
Figure 5. Effects of plant height (a), basal diameter (b), and SLA (c) on essential oil yield and yield rate in Cinnamomum camphora var. linaloolifera leaves.
Figure 5. Effects of plant height (a), basal diameter (b), and SLA (c) on essential oil yield and yield rate in Cinnamomum camphora var. linaloolifera leaves.
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Figure 6. Effects of different nitrogen fertilization rates on the relative abundance of linalool (a) and other major volatile compounds (b) in the essential oil of Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
Figure 6. Effects of different nitrogen fertilization rates on the relative abundance of linalool (a) and other major volatile compounds (b) in the essential oil of Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively. Different lowercase letters indicate significant difference among the treatments (p < 0.001).
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Figure 7. Effects of different nitrogen fertilization rates on the number of volatile compound types in the essential oil Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively.
Figure 7. Effects of different nitrogen fertilization rates on the number of volatile compound types in the essential oil Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively.
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Agronomy 15 01387 g008
Figure 8. Effects of different nitrogen fertilization rates on the relative abundance of volatile compounds in the essential oil of Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively.
Figure 8. Effects of different nitrogen fertilization rates on the relative abundance of volatile compounds in the essential oil of Cinnamomum camphora var. linaloolifera leaves. N0 represents no nitrogen fertilizer treatment; N45, N90, N135, and N180 represent nitrogen application rates of 45, 90, 135, and 180 kg·hm−2, respectively.
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Figure 9. Effects of plant height (a) and SLA (b) on the relative abundance of linalool and hydrocarbons in the essential oil of Cinnamomum camphora var. linaloolifera leaves.
Figure 9. Effects of plant height (a) and SLA (b) on the relative abundance of linalool and hydrocarbons in the essential oil of Cinnamomum camphora var. linaloolifera leaves.
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Table 1. Fertilizer consumption under different treatments.
Table 1. Fertilizer consumption under different treatments.
TreatmentN/kg·hm−2P2O5/kg·hm−2K2O/kg·hm−2
N009090
N45459090
N90909090
N1351359090
N1801809090
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Liu, Z.; Chen, X.; Zhao, J.; Sun, L.; Guo, J.; Shao, Y.; Liu, J.; Zhong, L.; Zhang, H.; Wang, Y.; et al. Threshold Effects of Nitrogen Fertilization Rates on Growth and Essential Oil Yield with Component Regulation in Cinnamomum camphora var. linaloolifera. Agronomy 2025, 15, 1387. https://doi.org/10.3390/agronomy15061387

AMA Style

Liu Z, Chen X, Zhao J, Sun L, Guo J, Shao Y, Liu J, Zhong L, Zhang H, Wang Y, et al. Threshold Effects of Nitrogen Fertilization Rates on Growth and Essential Oil Yield with Component Regulation in Cinnamomum camphora var. linaloolifera. Agronomy. 2025; 15(6):1387. https://doi.org/10.3390/agronomy15061387

Chicago/Turabian Style

Liu, Zhirong, Xinyi Chen, Jiao Zhao, Luyuan Sun, Jian Guo, Yangyang Shao, Jia Liu, Lei Zhong, Haiyan Zhang, Yanbo Wang, and et al. 2025. "Threshold Effects of Nitrogen Fertilization Rates on Growth and Essential Oil Yield with Component Regulation in Cinnamomum camphora var. linaloolifera" Agronomy 15, no. 6: 1387. https://doi.org/10.3390/agronomy15061387

APA Style

Liu, Z., Chen, X., Zhao, J., Sun, L., Guo, J., Shao, Y., Liu, J., Zhong, L., Zhang, H., Wang, Y., & Zhang, J. (2025). Threshold Effects of Nitrogen Fertilization Rates on Growth and Essential Oil Yield with Component Regulation in Cinnamomum camphora var. linaloolifera. Agronomy, 15(6), 1387. https://doi.org/10.3390/agronomy15061387

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