Introduction
Since ancient times, herbal medicine has been in great demand and keeps increasing day by day today, especially in industrialized countries [1]. Noting that the World Health Organization (WHO) has stated that about 65% to 80% of the world’s humanity in evolving countries use aromatic and medicinal plants for their primary health care [2]. On the other hand, developing countries [3], which view other difficult economic situations [4], do not have the means to use modern medicine [5]. Therefore, they have access to traditional medicine to heal themselves [6]. Currently, plant-based products offer a compelling reservoir of contemporary active ingredients for combating diverse diseases [7]. Aromatic and medicinal plants hold a crucial role in human existence [8], brimming with virtues that can be harnessed for a multitude of purposes [9]. Aromatic and medicinal plants represent an extraordinary source of antidotes and constitute a reservoir of plant-based medicine [10]. Man retains ancestral relationships with aromatic and medicinal plants for his needs [11].
Indeed, climate change has significant implications for plant life cycle events, ecosystem services, and cultural practices [12]. Climate change can alter the timing of key life cycle events in plants, including flowering, fruiting, and leaf senescence [13]. Warmer temperatures can cause these events to occur earlier than usual, disrupting the natural synchrony between plants and their pollinators, or seed dispersers [14]. Impacts on plant reproduction and ecosystem dynamics: The disruption of plant-pollinator or plant-seed disperser interactions can have cascading effects on plant reproduction and ecosystem dynamics. Reduced pollination or seed dispersal can lead to decreased plant fitness, altered plant community compositions, and changes in ecosystem processes such as nutrient cycling and trophic interactions [15]. Overall, climate change can have far-reaching consequences for plant-related ecological processes, ecosystem services, and cultural practices [16]. Understanding and addressing these impacts are crucial for effective conservation efforts, sustainable resource management, and the preservation of traditional knowledge and practices associated with plants [17].
However, climate change is currently modifying the morphological and physiological processes of aromatic and medicinal plants, which can negatively affect the chemical composition of secondary metabolites and essential oils.
This study aims to evaluate the influence of stressful conditions on the physiological behavior of some plants in response to climate change.
Materials and Methods
Study Area
Situated in the northern part of the Kingdom of Morocco, the province of Taounate covers an expansive area of 5616 km2. As of the 2014 census, its population stood at 662,246 inhabitants. Notably, approximately 87% of this population calls the rural areas home, emphasizing the predominantly agrarian nature of the province. Taounate, with its abundant natural resources, strong rural identity, human capital, and rich cultural heritage, holds substantial promise for sustainable development. Harnessing these valuable assets can play a pivotal role in fostering prosperity and enhancing the well-being of both the province and its residents.
Subculture of the Sample
Before transplanting, significant time and effort are dedicated to meticulously preparing the soil in our two fields. Several weeks in advance, we engage in thorough soil cultivation to thwart the proliferation of weeds, ensure a well-balanced blend of various soil factors, and mitigate the risk of root asphyxia when watering. This precise groundwork is geared towards creating optimal conditions for plant growth.
Furthermore, post-transplantation, our commitment extends to the regular removal of weeds on a weekly basis. This ongoing practice is crucial in preventing unwanted competition with our desired plants for vital nutrients. By eradicating these weeds, we guarantee that the intended plants have exclusive access to the resources they require for their optimal development.
By employing these diverse strategies, we ensure the cultivation of a thriving and robust crop in our fields.
The planting of the three sample sets was executed under varying levels of water stress for a year: 25% water stress for sample 1, 50% for sample 2, and 75% for sample 3. The study area encompasses 90 square meters, divided equally into three sections, each spanning 30 square meters [18].
Phytochemical Screening
The qualitative analysis process is geared towards establishing the presence or absence of specific compounds or groups of compounds in the samples. It encompasses a range of tests and techniques, including color reactions, precipitation reactions, various chromatographic methods (such as thin-layer chromatography and column chromatography), and spectroscopic approaches. Through the application of these methods, researchers can discern the categories of metabolites present in the plant samples, which may encompass alkaloids, flavonoids, tannins, terpenoids, saponins, phenolic compounds, and other chemical constituents.
Following the identification of the major families of primary and secondary metabolites via qualitative analysis, the next step involves quantitative assays to determine the concentrations or levels of these metabolites. The quantification of secondary metabolites was carried out according to the protocols of Gössling et al., Wang et al., and Sautner et al. [12-14]. These methodologies are designed to provide a reliable framework for accurately measuring and determining the levels or concentrations of the identified metabolites in plant samples.
Quantitative analysis employs a range of techniques, including spectrophotometry, high-performance liquid chromatography (HPLC), gas chromatography (GC), mass spectrometry (MS), and various other analytical methods. These techniques offer a more precise determination of the quantity or concentration of specific metabolites present in the samples. The quantitative data acquired through these analyses plays a critical role in evaluating the potential therapeutic or bioactive properties of the plants under study.
The insights obtained through phytochemical screening, encompassing both qualitative and quantitative dimensions, bear substantial significance for advancing research and development in domains like natural product chemistry, pharmacology, and plant-derived therapeutics. It offers valuable insights into the chemical composition of plant samples, aids in the identification of potential bioactive compounds, and enhances our understanding of their therapeutic properties and potential applications [15-17].
Essential Oils
In this study, the plant material utilized consisted of dried leaves, which were carefully preserved in the shade to maintain their chemical composition. To obtain the essential oils from these dried leaves, a Clevenger-type apparatus was employed. This type of apparatus is widely recognized for its application in the hydro-distillation method of essential oil extraction.
Approximately 100 grams of the dried leaves were loaded into the apparatus, and the extraction procedure was conducted using hydro-distillation. Hydro-distillation is a method that employs water as a solvent to extract the volatile aromatic compounds, including essential oils, from the plant material. The design of the apparatus facilitates the separation of essential oils from the water and the subsequent collection of these valuable oils [18].
Gas Chromatography (GC)
In the gas phase chromatography analysis, the extracted essential oils underwent further examination using a flame ionization detector (FID) in conjunction with two capillary columns of differing polarities. Specifically, the capillary columns employed were OV. 101 (25 meters long, with a diameter of 0.22 mm and a film thickness of 0.25 µm) and Carbowax 20 M (also 25 meters in length, with a diameter of 0.22 mm and a film thickness of 0.25 µm).
The analysis was conducted with a programmed oven temperature, where the temperature ranged from 50 to 200ºC. This temperature gradient increased at a rate of 5ºC per minute, facilitating a gradual temperature rise during the analysis. This programmed temperature sequence was designed to effectively separate and detect various volatile compounds within the essential oils based on their boiling points and volatility.
In this chromatographic system, helium gas was utilized as the carrier gas, flowing at a rate of 0.8 ml per minute. The carrier gas serves as the mobile phase, transporting the vaporized essential oil compounds through the capillary columns and towards the detector.
The flame ionization detector (FID) is a commonly employed detector in gas chromatography. It functions by measuring the ionization current generated through the combustion of organic compounds in a hydrogen-air flame. The FID furnishes a quantitative measurement of the separated compounds, as the ionization current is directly proportional to their concentration.
By implementing gas phase chromatography with the FID detector, combined with the use of various capillary columns, this analysis offers detailed insights into the individual chemical constituents found within the essential oils. This technique facilitates the identification and quantification of specific compounds, thereby contributing to a deeper understanding of the chemical composition and potential therapeutic properties of the essential oils [22, 25].
Results and Discussion
Quantitative Analyses
Primary Metabolites
The data in Fig. 2 reveals substantial variations in the composition of simple food components among the five plant species under study. Proteins consistently represent the highest percentage, with values ranging from 5.76% to 10.13%. Carbohydrates follow, with percentages spanning from 3.02% to 8.21%, while dietary fibers range from 2.01% to 4.7%, and lipids vary from 0.05% to 1.56%.
Furthermore, it’s evident that the composition of these simple food components responds to changes in water stress levels. Generally, these percentages decrease as water stress severity intensifies. This phenomenon is observed across all plant species studied.
Examining specific plants:
Inula viscosa: Proteins range from 7.01% to 10.13%, carbohydrates from 6.3% to 8.21%, lipids from 0.7% to 1.56%, and dietary fiber from 3.2% to 4.43%.
Salvia officinalis: Proteins range from 6.86% to 7.13%, carbohydrates from 3.02% to 6.21%, lipids from 0.52% to 1.35%, and dietary fiber from 2.34% to 4%.
Mentha pulegium: Proteins range from 6.8% to 7.23%, carbohydrates from 4.01% to 6.31%, lipids from 0.7% to 1.37%, and dietary fiber from 2.01% to 4.7%.
Thymus vulgaris: Proteins range from 5.76% to 6.43%, carbohydrates from 5.08% to 5.76%, lipids from 0.05% to 1.45%, and dietary fiber from 2.01% to 4.76%.
Rosmarinus officinalis: Proteins range from 7.14% to 7.61%, carbohydrates from 5.64% to 7.61%, lipids from 0.98% to 1.48%, and dietary fiber from 2.93% to 4.96%.
These findings highlight both the distinctive nature of each plant’s composition and the impact of varying water stress levels on the nutritional content of these plants. The findings have been validated by [26-28], revealing that water deficiency directly affects photosynthetic activity and the translocation of mineral salts from the soil to the roots. Additionally, [29-31] has affirmed that water scarcity influences both growth and nutrient supply. Similarly, [32-36] they discovered that environmental stresses have a detrimental impact on primary metabolites and their concentrations.
The results regarding the variation in mineral composition are depicted in Fig. 3, revealing that the most prevalent mineral compounds are Mg, Fe, Mg, K, and Mn. These minerals exhibit varying percentages, both among different plant species and within different samples of the same species. In terms of the highest percentage of mineral compounds, Inula viscosa takes the lead, followed by Mentha pulegium, Thymus vulgaris, Rosmarinus officinalis, and finally Salvia officinalis. Thus, the percentage of mineral compounds decreased from sample one to sample two, to sample three by decreasing the irrigation, as found in [37], which found that water stress slows down the passage of water to the roots, which causes the passage of nutrients to decrease.
Secondary Metabolites
In Fig. 4, the percentages of secondary metabolites in the extracts from the five plants most widely used by the rural population are presented in relation to the decrease in water availability. Sample two consistently stands out with higher concentrations of these metabolites, while sample three generally exhibits relatively lower concentrations compared to sample one. Generally, the percentage of secondary metabolites in successive order is as follows: alkaloids, flavonoids, saponins, tannins, and coumarins.
For a more detailed breakdown of each plant’s secondary metabolites with their respective percentages:
Inula viscosa: Alkaloids range from 11.85% to 13.85%, flavonoids from 4.42% to 8.9%, tannins from 3.14% to 7.46%, saponins from 5.52% to 6.26%, and coumarins from 1.44% to 2.05%.
Salvia officinalis: Alkaloids range from 5.54% to 12.43%, flavonoids from 2.11% to 8.53%, tannins from 0.12% to 2.55%, saponins from 3.22% to 3.78%, and coumarins from 0.15% to 1.11%.
Mentha pulegium: Alkaloids range from 5.82% to 12.7%, flavonoids from 2.16% to 4.96%, tannins from 0.11% to 1.51%, saponins from 3.28% to 3.87%, and coumarins from 0.24% to 1.74%.
Thymus vulgaris: Alkaloids range from 4.43% to 13.51%, flavonoids from 3.66% to 6.43%, tannins from 0.2% to 1.47%, saponins from 3.89% to 4.18%, and coumarins from 0.47% to 1.27%.
Rosmarinus officinalis: Alkaloids range from 3.43% to 10.38%, flavonoids from 6.17% to 11.93%, tannins from 2.12% to 3.61%, saponins from 6.84% to 10.48%, and coumarins from 1.67% to 4.16%.
Table 1.
Chemical compositions of essential oils of Inula viscosa.
Table 2.
Chemical compositions of essential oils of Mentha pulegium.
Table 3.
Chemical compositions of essential oils of Thymus vulgaris.
These results underscore how variations in water availability impact the composition of secondary metabolites in these plants. Sample two consistently displays higher concentrations, suggesting its response to fluctuating environmental conditions. These findings carry implications for comprehending the potential bioactive properties of these plants and their adaptability to fluctuating water conditions, which hold significant relevance for rural communities [38] Water stress has been identified as a factor that can impact and elevate the content of secondary metabolites [39]. This observation aligns with [40], who determined that high levels of secondary metabolites are associated with stress conditions. Furthermore, [41] noted that water-deficient plants exhibit heightened levels of secondary metabolites. In concurrence, [42] and [43] found that plants under adverse climatic conditions display the highest concentrations of secondary metabolites. Also [39-42] confirmed that stressful environmental conditions lead to the modification of the secondary metabolite profile of plants.
Table 4.
Chemical compositions of essential oils of Rosmarinus officinalis.
Essential Oils Yield and Gas Chromatography
The data regarding the yield of essential oil is depicted in the graph presented in Fig. 5. It’s evident that Thymus vulgaris yields the highest amount of essential oil, followed by Rosmarinus officinalis, Mentha pulegium, Salvia officinalis, and lastly, Inula viscosa. Across all five plants, sample two consistently stands out with the highest essential oil yield compared to the other two samples. This observation implies that sample two demonstrates the highest essential oil production efficiency for each of the studied plant species, as supported by [48], which indicates that plants experiencing moderate stress exhibit the highest essential oil yield compared to those under severe stress.
Additionally, [49, 50] reported that non-irrigated plants display the highest content of essential oils [51], and those who found that oil yield increases under stress conditions, [52] indicated that increasing temperatures can increase essential oil content. Thus, [48-52] found that water stress and increased temperature can cause alterations in the physiological and morphological processes of plants and the yield and chemical compositions of essential oils.
The chemical composition analysis of essential oils from the five plants (Tables 1, 2, 3, 4, and 5) reveals that the primary compounds in these essential oils are influenced by the reduction in irrigation. In most of the plants studied, the major compounds tend to increase under moderate water stress conditions. However, as environmental conditions deteriorate further, the predominant compounds in the essential oils begin to decrease. This suggests that the composition of essential oils is dynamic and responsive to changes in water availability, with a shift towards increased production of major compounds under moderate stress, but a subsequent decline as water stress intensifies [58]. The content of thymol increases with water stress, as did [59], who found that the yield of camphor increases with increasing levels of water stress, and [60], who obtained that the yield of 1,8-cineole, camphene, and β-pinene increases under stressful conditions.
The identification of major compounds in Mentha pulegium essential oils, such as polygonum, piperitenone, carvone, and dihydrocarvone offer valuable insights into the chemical makeup of this medicinal plant. However, the influence of climate change on the abundance and composition of these compounds adds another layer of complexity to our understanding of Mentha pulegium essential oil production. Climate factors, specifically temperature and precipitation, play a pivotal role in shaping the chemical profile of these essential oils.
Table 5.
Chemical compositions of essential oils of Salvia.
As illustrated in the accompanying figure, variations in climate conditions result in differences in the yield and distribution of these compounds among different samples. Pulegone, identified as the primary compound, exhibits varying percentages across the samples, with sample two demonstrating the highest concentration. These findings underscore the sensitivity of Mentha pulegium to climate change and its potential impact on essential oil production. Comprehending the underlying mechanisms behind these variations is crucial for predicting and managing the effects of climate change on medicinal plant resources. Extensive analysis and investigation are needed to unravel the intricate relationship between climate parameters and the adaptive responses of Mentha pulegium. This will provide invaluable insights into its medicinal properties and potential implications for traditional medicine and the development of natural products [47-49]. Additionally, other studies, such as those cited in [64, 65], support the finding that water stress significantly affects the abundance of the majority of compounds. Moreover, [66] asserts that ecological factors exert a substantial influence on the predominant compounds found in plants. These collective findings underscore the significant impact of stressors, encompassing water stress and ecological factors, on the composition and concentration of major compounds within medicinal plants. Such insights are of utmost importance for comprehending how these plants adapt to environmental conditions. They can also play a pivotal role in fine-tuning cultivation practices, thereby ensuring the quality and efficacy of plant-based products, especially in the context of shifting environmental factors. This knowledge is invaluable for sustainable resource management and the continued utilization of these plants for various applications, including traditional medicine and natural product development. The chemical compounds of plant essential oils are also modified by stressful conditions, as they found [67-71].
Conclusions
Aromatic and medicinal plants hold a pivotal role in our daily lives, emphasizing the pressing need to preserve them to ensure their sustainability for future generations. Currently, due to the combined impact of climate change and human activities, this natural wealth is deteriorating, both in terms of biodiversity and physiological and morphological aspects. It becomes imperative to anticipate the consequences of climate change on the physiological processes of these plants.
The results obtained from our study reveal that, across all three samples of the five plant species examined, the content of carbohydrates, lipids, proteins, and dietary fibers decreases as the level of irrigation decreases. In contrast, for secondary metabolites, sample two consistently displays the highest percentage compared to the other two samples. Similarly, in the case of essential oil yield, there is an initial increase in the content of essential oils during the first two years. However, as climatic conditions become more severe, the essential oil yield starts to decline. Moreover, chromatographic analysis illustrates that the major compounds within the essential oils of these plants undergo alterations under stress conditions.
Based on these findings, it becomes clear that the preservation of these crucial plant resources and an in- depth understanding of their responses to environmental stressors are essential for ensuring their sustained availability and the quality of essential oils and other plant-based products.
