Introduction

Arid regions are considered extreme milieus where the weather conditions are out from the acceptable range of survival of many plant species. Lower precipitations, higher temperatures, lower soil moisture contents, and higher evaporation rates are the major environmental factors that affect plants physiology in the arid regions1,2. To date, climatic change remains the main concern, and significant variations have been observed in the frequency and the intensity of the weather parameters. These adjustments in weather conditions might consistently increase at a rate faster than the global average in the arid regions compared to other geographical zones. In the United Arab Emirates (UAE), while temperature rates showed increasing trends from 0.3 to 2.8° C between 1980 and 20203,4, rainfall patterns experienced opposite trends5. In the environment facing extreme conditions, beneficial interactions between plant species can constitute an important key factor of survival of the understory plants. In this regard, microclimate of the understory plants could be greatly and positively affected by more nutrients which are critical for plant functioning6. Intensive research works have been conducted and addressed on this thematic7,8. However, almost no published data exist detailing how these ecological constraints affect plants ecosystems in the arid environments.

The movements of sun during the day strongly influence photosynthetic rates and plants metabolism regardless the overstory and the understory layer. There are important variations in light quality and quantity in the daytime, and these variations could be much higher in the extreme environments compared to other regions9,10,11. Simulating the impacts of sunlight on the growth performance of understory plants in the subtropical region of Karst12, found that thinning ecosystem plantation positively and significantly improved the establishment of those plants. Considering climatic regions affected by high precipitations and where plants populations densities are much higher, then plant growing under the trees might not receive optimal light which is crucial for the photosynthetic machinery. However, opposite trends could be observed in the regions experiencing extreme conditions especially in the summer exposed to daily temperatures that can reach 50° C13. For example, biomasses of understory plants were reported to be higher inside the canopy of Acacia trees than the open area in the semi-arid region of Ethiopia6. Therefore, such published data might not allow to fully understand these biological processes in the extreme zones.

Trees canopies not only provide shade and nutrients to the understory plants, but overstory layer could also act as light filter. As per this, understory plant metabolism might considerably change according to their position under the tree14. recorded significant changes within the canopy of Solanum melongena with lower canopy position receiving more far-red light than the other canopy positions. Corroborating findings have been reported by15 in apple tree. Furthermore, correlating photosynthetic photon flux density (PPFD) variable with plant growth16, observed a net increase in fresh and dry weight biomasses and morphological characters in the vegetable soybean. Moreover17, found greater increment in the photosynthetic parameters including CO2 concentrations, stomatal conductance and biochemical attributes in the plants growing under closed canopies than those exposed to full sunlight.

Globally, plants of the desert systems face more environmental stressful conditions than the other. Therefore, most of those plants and especially the perennials have adjusted their mechanisms of survival to cope with the changes occurring in their surrounding habitats. Nutrients storage is vital for plant functioning, and reserves accumulation might greatly change from organ-to-organ according to the plants demand and the environmental constraints. As per this, the quality and the quantity of the nutrients stored per organ could determine the capacity of each plant species to withstand with extreme conditions. Based on this18, found important variations between some wild plants of UAE with leaves containing more nutrients and mineral than the stem. Similar statements have been addressed by19 in Solanum erianthum plant. With focus on the plant organ-age, the levels of phosphorous, potassium, and magnesium have been found decreasing with the increase of the plant age20.

Plant canopy position has strong effects on the physiology of the understory plants and the impacts could be more important in the geographical zones facing harsh conditions than the other. Accordingly, exploring the phytochemical composition of those plants could allow to identify novel metabolites that could be used to fight against microbes resistant to antibiotics. Over the past decades, researchers have attempted to experiment various methods that could allow to solve the problem related to microbes resistant to antibiotics, but this health issue is still growing faster globally, and many microbial strains have been identified21. Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Aspergillus niger, Bacillus subtilis, Candida albicans, and Staphylococcus aureus are considered the most critical microorganisms that cause significant damages to human health. E. coli is ranked by the World Health Organization (WHO) as the third most resistant pathogens to antibiotic causing important damage within human population22. The adverse effects of E. coli and K. pneumonia on human body include urinary tract, bloodstream, and prostatitis infections23,24. Furthermore, K. pneumonia has been documented to cause meningitis and the chances for the pregnant woman to give birth to premature infants are higher when exposed to this pathogen during the pregnancy period25. A. niger can adversely alter human body by causing otomycosis, cutaneous and pulmonary infections26. Although many fungal strains can significantly alter human health, Candida species remain the predominant cause of invasive fungal infections with around 150 million mucosal infections and 200,000 deaths per year27. To date, microbial resistant to antibiotic is the major concern globally and still, no drug has been discovered to completely eradicate their nuisances. Therefore, exploring the mechanisms of adaptations of the native plants growing in the extreme environments might help in identifying novel metabolites with strongest antimicrobial effects.

Tephrosia apollinea is a small perennial shrub native to UAE ranked under Fabaceae family (Fig. 1). This plant is found growing in many habitats in the Emirate of Fujairah including roadside, stony and rocky places, and abandoned farms. T. apollinea plants are also found growing under the canopies of Acacia trees. Medicinally, plant parts of T. apollinea have been reported by the local people to possess many medicinal properties that can be used to improve human health. In the traditional medicine, T. apollinea plants parts have been used to treat earache, wounds, nasal congestion and bones fractures28. Furthermore, previous studies demonstrated that extracts resulting from this plant can be used as anticancer, antidiabetic, and antimicrobial29.

Fig. 1
figure 1

Plant of Tephrosia apollinea (A) and the flowers (B) growing in the Emirate of Fujairah.

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Overstory plants canopies can enhance the adaptabilities of the understory plants facing harsh conditions. Plant growing beneath the trunk might present very interesting phytochemical composition than those exposed to full sunlight, which could be used to improve medicines production. While some earlier studies have attempted to evaluate the impacts of the overstory plants over the understory6,17, almost no available literature review exist addressing these biological phenomena in the arid regions. Furthermore, almost no published data exist explaining how minerals and nutrients distribution could constitute an important key factor that can enhance the stress tolerance levels of the understory plants in the arid regions. Moreover, there is a lack of scientific information examining the impacts of natural light on the understory plant in the extreme environments. Intensive research works have been completed exploring the use of plant species to improve medicine production. However, most of the previous works had no much interest in considering plant organ-age, and canopy position.

Therefore, the present research work was designed to evaluate the impacts of canopy positions of Acacia tortilis (open area, east and west) on the phytochemical composition and medicinal properties of Tephrosia apollinea (understory plant) emphasizing plant-organ, plant organ-age. Furthermore, the present work also attempted to quantify the impacts of natural light emphasizing PPFD values on the native understory plant T. apollinea considering canopy position.

Materials and methods

Site study and samples preparation for the analyses

Full mature plant organs of Tephrosia apollinea considering organ-age (young and mature leaves, young and mature branches) were collected in the Emirate of Fujairah during November 2023 beneath Acacia tortilis trees (east and west sides) and open area (Figs. 2 and 3).

Fig. 2
figure 2

Mapping point for Acacia tortilis and Tephrosia apollinea: Zone of plant collection. The map was performed through the Sentinel-2 image having 20-m spatial resolution, dated 23-1-2024, which was obtained from the Earth Observation (EO) Browser (https://www.sentinel-hub.com/explore/eobrowser/). Thereafter, the final map composition was obtained using the software ArcGIS 10.4 version.

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In UAE, November is one of the autumn months which is the transitional season between the hot summer and the winter with temperature ranging from 24 to 34° C. Furthermore, almost no rainfalls occur in this period of the year. The study was conducted in the environment with mature plants of Acacia tortilis and Tephrosia apollinea plants. The studied plant species was taxonomically identified by Dr. François, Botanist in the Plants Department, Fujairah Research Centre supporting by the literature review. The tested plant samples of T. apollinea, and habitat information in addition to the associated botanical data have been deposited in the Seed Bank and Herbarium of Sharjah under the voucher number 4085.

Fig. 3
figure 3

Acacia tortilis canopy size and Tephrosia apollinea plants growing under A. tortilis plant and in the open area.

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The collection was performed based on the plant organ-age (young and mature parts), and the organ-age was identified according to the phenotype of each plant organ and their location on the plant (Fig. 4). Furthermore, young and mature leaves were characterized by a total number of 07 and 11 leaflets respectively. While the internode between 02 young leaflets was estimated at 6 mm, the mature leaves had 10 mm. With focus on the colours, both sides of the mature leaves were lighter green than the young leaves. For the analyses a total of 03 Tephrosia apollinea plants were collected per canopy position and per Acacia tortilis tree. The collected plants were then segregated into young and mature leaves, young and mature branches, and the estimated amount of 700 g were prepared per sampling plant organ for the testing. Plants sampling adhered to ethical standards and legal guidance applicable to collect plants samples in unrestricted environment in UAE. An authorization letter to collect the experimental plant samples has been submitted as supporting document.

Fig. 4
figure 4

Young leaves (a) and young branches (b), mature leaves (c) and mature branches (d), young and mature leaves sizes (e) and (f).

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Collected plant parts of T. apollinea were kept in the ice box and then taken to the laboratory for the analyses (Table 1). Prior carrying out the different analyses, the sampling plant organs were washed using running tap water and rinsed thrice from distilled water.

Chemical analyses

Table 1 Tested parameters of Tephrosia apollinea and the methods.
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Antimicrobial activities: inhibition zone

Microbial assessments were conducted according to33,34 following the Disk Diffusion Technique (ISO 16782:2016). Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus were tested as bacteria strains, and Candida albicans and Aspergillus niger the fungal strains. Briefly, bacterial were cultured on Muller Hinton broth (MHB) and allowed to growth for 24 h at 37° C. Thereafter, growing bacterial suspension was adjusted to 0.5 McFarland units followed by loading the filter paper disc with 10 µl of each plant organ extract of Tephrosia apollinea. The antifungal activities tests were similar to those of the bacteria with slight emendations. Here, the culture medium used was the combination of Mueller Hinton, 2% glucose and 0.5 g/ml methylene blue. Afterward, all the plates were kept in the incubator adjusted at 37° C for 24 h. Subsequently, the inhibition zone that determines the activities of the microorganism was assessed in millimeters.

Environmental parameters assessments

The assessments on Photosynthetic Photon Flux Density (PPFD) were conducted in two different periods of the day (morning: 8–9 am and evening: 4–5 pm) during two following days. The readings considered three plant locations including open area and under Acacia tortilis (east and west). Data collections were performed using Licor 180 spectrometer device (Licor, Lincoln, NE, USA). Three plants of Tephrosia apollinea growing under three Acacia tortilis from the two experimental locations (east and west) were selected to assess the incident light, and the readings were obtained at the distance of 5 cm on top of the experimental plant. The other readings were performed in the open area away from any existing A. tortilis plants. Temperatures and rainfalls data of 09 years (2016–2024) were obtained from the National Centre of Meteorology (NCM) of UAE.

Data analysis

The data collected in this work were analysed in triplet and two-way analysis of variance (ANOVA) were conducted to evaluate the effects of plant locations (open, east, and west) and the daytime periods (morning and evening) on the values of the incident light. Furthermore, two-way ANOVA were carried out to test the impacts of plant locations and plant organ-age (young and mature leaves, young and mature branches) on the minerals, phytochemical composition and medicinal properties of Tephrosia apollinea. Temperatures and rainfalls data were averaged and then the values were used to create Line Chart graphs. Heatmap correlations were performed through Python to identify relational effects between the tested plant attributes. Tukey test (honestly significant differences, HSD) was applied to identify significant differences between the means at p < 0.05, and all the data were statistically analysed through SYSTAT (version 13.0).

Results

Temperatures variations between 2016 and 2024 and within the tested months in the Emirate of Fujairah

In general, the tested years showed similar trends according to the months of study. A net increase in temperatures was observed from January to June and then a decrease trend was noticeable from June to December month (Fig. 5). Lower temperatures were recorded between January and February with the values of 21.2 °C and 22.3 °C respectively, while highest temperatures were observed between June and July and the values were 34.7° C and 34° C respectively. Overall, June month of year 2024 was hottest (36 °C) than the other months and the other years.

Fig. 5
figure 5

Temperatures variations over the time in months and years in the Emirate of Fujairah.

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Rainfalls variations between 2016 and 2024 and within the tested months in the Emirate of Fujairah

In sum, rainfalls occurred between January to May, and October to December for most of the tested years (Fig. 6). However, occasional rainfall was also observed between August and September 2017 with an estimated amount of 1.6 mm. Overall, the values of rainfalls 42.1 mm and 8.8 mm were found between January and May months, while 12.13 mm and 107.3 mm were recorded between October and December. In general, December 2017 received more rainfalls (107.3 mm) than the other months and the other sampling years.

Fig. 6
figure 6

Rainfalls variations depending on the time in months and years recorded in the Emirate of Fujairah.

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Rainfalls variations depending on the time in years in Fujairah

The recorded data on the rainfalls showed different trends depending on the tested years (Fig. 7). In general, rainfalls were disproportionately distributed over the tested years. While lower rainfalls (8 mm) were receiving in 2021, highest values (32.3 mm) were recorded in the year 2019. There were no changes in the amounts of rainfalls received between the years 2023 and 2024.

Fig. 7
figure 7

Rainfall variations occurring in Fujairah depending on the time in year.

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Effects of plant locations (open, east, and west) and daytime periods (morning and evening) on the sunlight variables

Statically, plant locations and daytime periods, and their interactions had significant (p < 0.001) effects on the values of incident light (Fig. 8; Table 2). In sum, the values of PPFD (1351.3 µmol.m− 2.s− 1), PFD-UV (24.87 µmol.m− 2.s− 1), PFD-FR (404.78 µmol.m− 2.s− 1) were greater in the open area in the morning time than the other plant locations.

Fig. 8
figure 8

Impacts of plant locations (open, east, and west direction) and daytime periods on the incident light variables. The values not sharing the same letters are significant at p < 0.05 as per Tukey test.

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Table 2 Results of ANOVA testing the effects of plant location (open, east, and west) and the daytime periods (morning and evening) on the incident light.
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Impacts of plant locations (open, east, and west) and plant organ-age (young and mature leaves) on the mineral contents of Tephrosia apollinea plant

Plant locations and plant organ-age, and their interactions had significant (p < 0.001) effects on the mineral contents of the young and mature leaves of Tephrosia apollinea (Fig. 9; Table 3). Nevertheless, no significant (p < 0.05) differences were observed on the values of magnesium when emphasizing plant organ-age. Overall, young leaves collected from the open area showed higher values of calcium (2820.6 mg/100 g), potassium (1677.76 mg/100 g), and magnesium (492.26 mg/100 g) than the mature leaves. Young leaves located at the east position revealed greater values of phosphorous (457 mg/100 g) compared with the mature while, mature leaves showed higher levels of manganese (7.46 mg/100 g) and copper (12.13 mg/100 g). At contrast, the amounts of zinc (9.13 mg/100 g) and sodium (291.86 mg/100 g) were much higher in the west location.

Fig. 9
figure 9

Effects of plant locations (open, east, west) and plant organ-age (young and mature leaves) on the mineral composition of Tephrosia apollinea. The values not sharing the same letters are significant at p < 0.05 as per Tukey test.

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Table 3 Results of ANOVA assessing the impacts of plant location (open, east, and west) and plant organ-age (young and mature leaves) on the minerals contents of Tephrosia apollinea.
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Effects of plant locations (open, east, and west) and plant organ-age (young and mature leaves) on the proximate and phytochemical analyses of Tephrosia apollinea

Plant locations and plant organ-age, and their interactions had significant (p < 0.001) effects on the tested variables of Tephrosia apollinea (Fig. 10; Table 4). In sum, young leaves collected in the open area had more crude protein (8.53%) while, the levels of crude fibre (10.73%) and ash (4.83%) were greater in the mature leaves. Contrary to the open area, mature leaves sampling from the east plant location showed higher amounts of tannins (2.42%) and total flavonoids (3162.66 mg/kg). The concentrations of dry matter (62.80%) and TDN (66.34%) were much higher in the mature leaves of T. apollinea collected from the west plant location. In general, the levels of fat were less than 0.1% for all the tested plant organs regardless the locations.

Fig. 10
figure 10

Effects of plant locations (open, east, and west) and plant organ-age (young and mature leaves) on the proximate and phytochemical analyses of Tephrosia apollinea. The values not sharing the same letters are significant at p < 0.05 as per Tukey test.

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Table 4 Results of ANOVA testing the impacts of plant location (open, east, and west) and plant organ-age (young and mature leaves) on the proximate and phytochemical parameters of Tephrosia apollinea.
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Impacts of plant locations (open, east, and west) and plant organ-age (young and mature branches) on the mineral composition of Tephrosia apollinea

Young and matures branches of Tephrosia apollinea plant samples were subjected to mineral analyses and the results of the statical analysis revealed significant (p < 0.001) effects on the tested chemical parameters (Fig. 11; Table 5). Overall, mature branches collected from the open location showed higher values of calcium (2015 mg/100 g) than the young and the other plant locations. The amounts of manganese (7.76 mg/100 g), and potassium (1577.86 mg/100 g) were found to be much higher in the young branches sampling from the east location compared with the mature and the other locations while the levels of phosphorous (357.53 mg/100 g) and sodium (285.6 mg/100 g) were greater in the mature branches. Comparably to the other locations, the concentrations of zinc (6.34 mg/100 g) and copper (14.13 mg/100 g) were more important in the young branches of T. apollinea collected from the west location while, the levels of magnesium (368.63 mg/100 g) were found to be greater in the mature branches.

Fig. 11
figure 11

Effects of plant locations (open, east and west) and plant organ-age (young and mature branches) on the mineral composition of Tephrosia apollinea. The values not sharing the same letters are significant at p < 0.05 as per Tukey test.

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Table 5 Results of ANOVA testing the impacts of plant locations (open, east, and west) and plant organ-age (young and mature branches) on the mineral contents of Tephrosia apollinea plants.
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Effects of plant locations (open, east, and west) and plant organ-age (young and mature branches) on the proximate and phytochemical composition of Tephrosia apollinea

Plant location and plant organ-age had significant (p < 0.001) effects on all the tested variables (Fig. 12 Table 6). In the open area, young branches of Tephrosia apollinea showed higher levels of tannins (1.52%) and total flavonoids (2316.5 mg/kg) than the mature and the other plant locations. However, the amounts of dry matter (75.05%), crude protein (6.75%), ash (6.45%), and TDN (68.64%) were greater in the young branches sampling from the west location while, the levels of crude fibres (12.24%) were found to be higher in the mature branches.

Fig. 12
figure 12

Impacts of plant locations (open, east, and west) and plant organ-age (young and mature branches) on the proximate and phytochemical analyses of Tephrosia apollinea. The values not sharing the same letters are significant at p < 0.05 as per Tukey test.

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Table 6 Results of ANOVA assessing the effects of the plant locations (open, east, and west) and plant organ-age (young and mature branches) on the proximate and phytochemical composition of Tephrosia apollinea.
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Effects of plant locations (open, east, and west) and plant organ-age (young and mature leaves) on the antimicrobial activities of Tephrosia apollinea: inhibition zone

Plant locations had significant (p < 0.05, and p < 0.001) effects on all the tested pathogens except Klebsiella pneumonia and Bacillus subtilis (Fig. 13 Table 7). However, no significance differences were recorded on the plant organ-age and their interactions with plant locations. In general, young leaves and east plant location had higher antimicrobial effects against the tested pathogens than the mature leaves and the other locations. Young leaves collected from the east location showed higher inhibition zone against Escherichia coli (14 mm), Klebsiella pneumonia (12 mm), Pseudomonas aeruginosa (13 mm), Aspergillus niger (14 mm) while, the effects were equal between the young and the mature leaves on Bacillus subtilis (11 mm) and Candida albicans (13 mm) collected from the east and west plant locations respectively. Comparably to the other plant locations, Staphylococcus aureus bacterium was more affected by the extract (13 mm) of the young leaves of Tephrosia apollinea collected from the west location.

Fig. 13
figure 13

Impacts of plant locations (open, east, and mature) and plant organ-age (young and mature leaves) on the medicinal properties of Tephrosia apollinea against Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Aspergillus niger, Bacillus subtilis, Candida albicans, Staphylococcus aureus. The values not sharing the same letters are significant at p < 0.05 as per Tukey test.

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Table 7 Results of ANOVA evaluating the effects of plant locations (open, East and west) and plant organ-age on the antimicrobial activities of Tephrosia apollinea against Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Aspergillus niger, Bacillus subtilis, Candida albicans, Staphylococcus aureus.
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Impacts of plant locations (open, east and west) and plant organ-age (young and mature branches) on the antimicrobial activities of Tephrosia apollinea: inhibition zone

Overall, no significant (p < 0.05) effects were found when considering the impacts of plant location and plant organ-age against the selected microbial activities (Fig. 14, Table 8). The only significant (p < 0.05) effects were observed in Pseudomonas aeruginosa, and Candida albicans when emphasizing plant organ-age and plant locations respectively. Antimicrobial effects of plant extracts of Tephrosia apollinea were equal (10 mm) in the young and mature branches collected from the open area, and these values were also equal to those recorded in the young branches collected from the east and west plant locations. Young branches sampling from the east plant location showed higher values of inhibition zone against Escherichia coli (12 mm), Klebsiella pneumonia (11 mm), Bacillus aureus (10 mm), Pseudomonas aeruginosa (11 mm) and Aspergillus niger (13 mm) than the mature branches, while the effects were equal (12 mm) on Candida albicans. In the west location, young branches plant extracts showed elevated values of inhibition zones against Staphylococcus aureus (12 mm), Klebsiella pneumonia (11 mm), Bacillus subtilis (10 mm), and Pseudomonas aeruginosa (11) than the matures branches.

Fig. 14
figure 14

Effects of plant locations (open, east, west) and plant organ-age (young and mature branches) on the microbial growth (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Aspergillus niger, Bacillus subtilis, Candida albicans, Staphylococcus aureus) treated with plant extract of Tephrosia apollinea. The values not sharing the same letters are significant at p < 0.05 as per Tukey test.

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Table 8 Results of ANOVA evaluating the impacts of plant location (open, east, and west) and plant organ-age (young and mature branches) on the microbial growth of Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Aspergillus niger, Bacillus subtilis, Candida albicans, Staphylococcus aureus exposed to Tephrosia apollinea plant extracts.
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Heatmap correlation between some the tested variables of Tephrosia apollinea

Open area

Analyses of relationship showed different types of effects between the tested parameters including negative and positive (Fig. 15). The reddish colour indicated either positive and moderate or strong effects, while blue colours highlight the negative relational effects.

Fig. 15
figure 15

Heatmap correlation between minerals contents and nutrients of Tephrosia apollinea growing in the open area. Legend: DM = dry matter, CP = crude protein, Cfi = crude fibre, TDN = total digestible nutrients, Tan = tannins, Fla = Total flavonoids, *p < 0.05, **p < 0.01, ***p < 0.001, ns = non-significant.

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East canopy position

Analyses of correlation between the tested variables indicated positive and negative relational effects in the east plant location (Fig. 16). Reddish colours indicated positive association between the parameters, while blue colours highlight the negative associational effects.

Fig. 16
figure 16

Heatmap correlation between the tested parameters of Tephrosia apollinea in the east location. Legend: DM = dry matter, CP = crude protein, Cfi = crude fibre, Tan = tannins, Fla = flavonoids, *p < 0.05, **p < 0.01, ***p < 0.001, ns = non-significant.

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West canopy position

The tested plant variables had different relational effects from negative to positive in the west plant location (Fig. 17). Reddish colour indicated the positive effects between the groups while blue colours highlighted negative effects respectively.

Fig. 17
figure 17

Heatmap correlation between the tested parameters of Tephrosia apollinea in the west canopy location. Legend: DM = dry matter, CP = crude protein, Cfi = crude fibre, TDN = total digestible nutrients, Tan = tannins, Fla = total flavonoids, *p < 0.05, **p < 0.01, ***p < 0.001, ns = non-significant.

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Discussion

The impacts of overstory plants over the understory have been reported in the earlier works6,7,10. However, very little is known about these effects in the arid regions. In the current work, canopy position of Acacia tortilis trees, plant organ, and plant organ-age showed significant effects on the phytochemical composition of Tephrosia apollinea. Furthermore, light variables were also found to importantly vary according to the plant canopy position. In general, PPFD, PFD-UV, and PFD-FR values were greater in the open area than east and west canopy position. T. apollinea located from the west canopy position were less exposed to sunlight than the other canopies positions. The findings obtained on the light quality in this study align with those reported by35. However, these values were greater than those addressed by36. In general, the amount of light received by any surface strongly depends on the intensity of the light and the exposition time. Clouds are considered the major factors that affect the amount of light that reach any surface, and the formation of clouds is linked to the temperature and atmospheric water vapor. Accordingly, light quality might importantly vary during the cloudy times than the cloudless periods. Desert systems are well-known to have very less cloudy days and months per year. With specificity to UAE, most of the cloudy times occur between January and April which coincide with the rainy season37. Therefore, light quality data presented in the current study, and which are greater than those reported in the earlier works, could be explainable by the months of experimentations which could have been exposed to the sky with no clouds.

Based on our results, the levels of calcium, potassium, magnesium, crude protein, crude fibre, and ash were significantly higher in the open area than beneath the trunk, and these amounts were also greater in the young than mature leaves. However, phosphorous, manganese, copper, tannins, and total flavonoids levels were found to be higher in the east canopy position with mature leaves showing higher concentrations whereas, sodium, zinc, dry matter and total digestible nutrients were found to be greater in the west canopy position. Unfortunately, the literature review is poorly documented in exploring the chemical composition of the understory plants considering canopy position globally and plant organ-age which could help understanding how overstory plant canopies affect the understory plants metabolism especially in the arid regions. The amounts of calcium (2850.6 mg/100 g), potassium (1677.76 mg/100 g), and magnesium (492.26 mg/100 g) recorded in the present work were much higher than those reported by38. In the current work, the values of PPFD, PFD-UV and PFD-FR were higher in the open area than those beneath the trunk, and west canopy position received less light than east. This would mean that Tephrosia apollinea plants were photosynthetically more active in the open area than the east and west canopies positions. The quality and the quantity of light that reach plant leaves or plant canopy are critical for the photosynthesis reactions but however, under certain levels of light intensity, photosynthesis machinery could be strongly affected39. Therefore, under such environmental adjustments, hormonal and enzymatic reactions could be activated to enhance the survival capacity of the exposed plants to cope with photooxidative stress.

In the present work, calcium and crude protein were found to be greater in the young leaves growing in the open area than mature and the other canopies positions. Calcium plays crucial role in plant functioning including cell elongation, and stomata movements, while proteins are involved in many physiological roles such as enzymatic, structural and functional. Plant growth can be significantly impaired under extreme environmental conditions. As per this, regulation in these phytochemical elements could be activated to support photosynthetic processes and maintain cell integrity through antioxidant production and gene expression. In general, climate of UAE is characterized by almost no rainfalls occurring between June and November. Based on our results, year 2024 was found to be hottest than 2023 and the other sampling years but however, rainfalls values were equal for these two years study, and lesser than the year 2019. With focus on the year 2023, only 16.7 mm of precipitations were received between June and December which were significantly lower than the other months. These variations observed in the weather conditions could be linked to the current climatic conditions. Increment in temperatures primarily affect soil ecosystems by reducing soil moisture contents and microbial activities which are specialized in the nutrients recycling40,41. Strategically, increasing the amounts of calcium within plant parts could help T. apollinea plant using water efficiently through stomata regulation.

Interestingly, while the levels of total flavonoids were still higher in the young branches collected from the open area, the amounts of crude protein were found to be much higher in the young branches collected in the east and west canopies positions. Based on our results, total flavonoids were positively and strongly correlated with PPFD values. Flavonoids are well-known for their role in helping plants surviving when exposed to abiotic stress, and one of the major functions of these chemical compounds is to inhibit the formation of reaction oxygen species during stressful conditions in plant42. In our work, PFD-UV values were greatly higher in the open area than east and west canopies positions. Light variables and especially PFD-UV could be importantly affected under environment with shaded than sunny sky. Shaded sky might considerably reduce the amounts of PFD-UV that could have reached any surface. Similarly to the shaded sky, overstory plant layer can also affect the level of ultraviolet that reaches plant leaves. Therefore, plant exposed to full sunlight might receive higher amounts of light than those shaded. As per this, overstory plant canopy can greatly help understory layer challenging the harsh conditions in the arid regions. Although PFD-UV play critical role in plant growth and development, important levels might strongly alter plant metabolism, and DNA denaturation through the formation of photoproducts, which could induce mutagenesis and cells death43. Therefore, flavonoid metabolism adjustments could be used by T. apollinea plants to enhance their survival capacity in order to cope with stressful conditions. In this regard, overstory plants layer can constitute an important key factor to consider in the processes of plant adaptations under arid regions.

During the past decades, scientists have enriched the literature review with intensive works on antimicrobial activities but the problem of microbes resistant to antibiotic is still growing faster, and this could constitute an important threat for the future generation. Furthermore, many earlier studies have tried to explore the impact of the overstory plants canopies over the understory but with almost no interest in linking this with plant medicinal properties. Moreover, there is a lack of published information considering canopy position and plants medicinal properties in the arid regions and other geographical zones globally, which could help optimizing the analyses and the tests for improving medicine. The current work was designed to understand how Acacia tortilis canopies affect the phytochemical contents and the medicinal properties of Tephrosia apollinea emphasizing plant organ types, plant organ-age, and canopy position.

In this study, young organs of Tephrosia apollinea including young leaves and young branches showed strongest antimicrobial activities than the mature organs. Additionally, leaves showed much higher antimicrobial effects than the branches. Higher variations in the leaves phytochemical contents and other plant organs have been reported in the previous works18,19. Therefore, the obtained results on antimicrobial activities presented in this work could be correlated with the nutrients contents. In general, plants metabolites including flavonoids and tannins can disrupt microbial metabolism by inhibiting enzymatic activities, which are involved in the protein and nucleic acid synthesis44. Alteration in protein and nucleic synthesis can result in cell wall and membrane damage. Furthermore, canopy position was found to significantly affect antimicrobial activities with plant of the east and west canopy position showing more effects than open area. These observations may be attributed to the phytochemical composition of the tested plants since more nutrients were noticeable in the east and west canopy positions than open area.

In the present work, the tested pathogens exhibited different responses when exposed to plant extracts of Tephrosia apollinea. Overall, young leaves collected from the east canopy position revealed highest inhibitory effects on Escherichia coli, and Aspergillus niger with 14 mm for the inhibition zone which was greatly higher than those reported by45 in Zingiber plant (10 mm), Prunica (12 mm), and Azadirachta indica (13 mm). The findings on antimicrobial activities against A. niger obtained in the present study were also significantly higher than those addressed by46 in Brucea antidysenterica (6 mm), Justicia schimperiana (6 mm), and Aleo vera (10.3 mm). E. coli and A. niger are considered the most critical pathogens with significant negative effects recorded on human physiology. As per our observations, plant samples of T. apollinea collected from these canopies positions could be used in the clinical tests to improve medicine production.

In the current work, the second most sensitive microorganisms were Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans with 13 mm of inhibition zone recorded from the young and mature organs collected from the east and west canopies positions of Acacia tortilis. Human health is continuously under threat due to the higher capability of microbes to quickly adjust their physiology according to the changes occurring in their environments. C. albicans is one of the most critical fungi in the group of Candida species that causes significant damages to human health than the other due to the adjustments in genes expression47. Therefore, exploring plants metabolites under different geographical regions and habitats-type can allow to identify and to isolate novel metabolites with strongest antimicrobial activities. The inhibition zone (13 mm) recorded in this work against S. aureus, P. aeruginosa, and C. albicans were greater than those documented by48,49.

In the current study, the least sensitive microorganisms were Klebsiella pneumonia, and Bacillus substilis with the inhibition zones of 12 mm and 11 mm respectively. These effects were much higher than those addressed by50 in Tephrosia hookeriana. Recent information on microbes resistance to antibiotics published by the World Health Organization (WHO) showed that pathogens resistance to antibiotics were directly responsible for approximately 700, 000 death and this is expected to reach 20 million by 205051. Microbiologically, inhibition zone analyses are critical for pre-diagnostic tests to determine the ability of the tested microorganism to cope with known environment. The results presented in this work are potentially strong to support scientific basis for the use of T. apollinea plants against many illnesses related to human health considering the other tested environmental variables. Furthermore, the contents in minerals and other plant nutrients can be integrated in the food processing in the arid regions to prevent food shortage.

Conclusion

In the current work, understory plant Tephrosia apollinea responded differently according to the canopy position of Acacia tortilis and open area. Plant organ types, and organ-age dependent also revealed important effects on the phytochemical analyses and medicinal properties of the tested plant. East canopy position received more light than west, but this was less compared to those exposed to full sunlight and the values of PPFD, PF-UV and PFD-FR were 750.84 µmol.m− 2.s− 1, 14.42 µmol.m− 2.s− 1, and 174.62 µmol.m− 2.s− 1 respectively, while those of the full exposed were 1351.3 µmol.m− 2.s− 1, 24.87 µmol.m− 2.s− 1, and 404.78 µmol.m− 2.s− 1. Young organs of T. apollinea plants growing in the open area showed elevated contents in calcium (2820.6 mg/100 g), potassium (1677.76 mg/100 g), magnesium (492.26 mg/100 g), crude protein (8.53%) and total flavonoids (2316.5 mg/kg) than the mature and other canopies positions. Contrastingly, nutrients levels were importantly higher in the east and west canopies positions than open area. Comparably with the leaves, crude protein contents (6.75%) were greater in the young than mature branches. Interestingly, antimicrobial activities of the tested plant were greater in the east canopy position than west and open area with more effects noticeable in the young organs than mature and the inhibition zones ranging from 10 to 14 mm. PPFD values were found to be strongly correlated with magnesium, dry matter, crude protein, ash, manganese, copper, total flavonoids, zinc, and TDN. The findings of the current work demonstrate that overstory plants canopies can increase stress resilience of the understory plants experiencing extreme conditions, and this could be potentially used to improve food and pharmaceutical industries in the arid climate. The current research work did not include pharmacological and toxicological tests which could help determining the doses with high efficiency to inhibit microbial activity in the animal body. Therefore, in order to complete this study, pharmacological and toxicology, and clinical tests should be conducted furtherly. Moreover, it is strongly recommendable to the Environmental Authority, and Environmental Agencies to take action in establishing conservation methods that will help preserving T. apollinea plants.