Performance of growth and remediation potency of Jacaranda mimosifolia in cadmium and lead contaminated soil

El-Mahrouk , E.-S., M.A. Ebrahim, H., Gaber , M. K., Aly , M. A., El-Naggar, A. A., Honfi, P., Tilly-Mándy, A., and Eisa, E. A. (2025). "Performance of growth and remediation potency of Jacaranda mimosifolia in cadmium and lead contaminated soil," BioResources 20(1), 1547–1576.

Abstract

In a 16-month study addressing global agricultural soil heavy metal contamination, researchers explored plant-centered solutions using Jacaranda plants. The impact of different combinations of cadmium nitrate (40, 80, and 120 mg) and lead nitrate (400, 800, and 1200 mg/kg soil) were evaluated relative to Jacaranda’s remediation capabilities. Employing a randomized complete block design with 8 applications across 3 repetitions, the study assessed growth traits and chemical characteristics. Untreated plants showed higher growth values, contrasting with reduced values in plants exposed to elevated cadmium (Cd) and lead (Pb) levels. For instance, the treatment with 120 mg Cd/kg soil + 1200 mg Pb/kg soil led to a 28% reduction in plant height, 13% in main stem diameter, 41% in branch number, and 35% in leaf area compared to the control. Despite these challenges, Jacaranda plants demonstrated resilience with a 100% survival rate. Plant organs showed increased Cd and Pb contents, with fallen leaves having lower metal content, mitigating pollution hazards. Post-planting, soil characteristics shifted, indicating Jacaranda‘s potential for Cd phytoextraction (BCF < 1 and, TF > 1) and Pb phytostabilization (BCF and TF < 1). The study establishes Jacaranda as a promising candidate for phytoremediation due to its resilience to elevated metal levels.

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**Performance of Growth and Remediation Potency of Jacaranda mimosifolia in Cadmium and Lead Contaminated Soil**

El-Sayed Mohamed El-Mahrouk,^a Hayam M.A. Ebrahim,^b Mohamed K. Gaber,^c Mahmoud A. Aly,^c Assem A. M. El-Naggar,^b Péter Honfi,^d,* Andrea Tilly-Mándy,^d and Eman Abdelhakim Eisa ^d,e,*

DOI: 10.15376/biores.20.1.1547-1576

Keywords: Phytoremediation; Contamination; Cadmium; Lead; Jacaranda mimosifolia

Contact information: a: Department of Horticulture, Faculty of Agriculture, Kafrelsheikh University, Egypt. elsayedelmahrouk@gmail.com; b: Horticulture Research Institute Alex. Branch (Antoniadis), Egypt. Hana_1812@yahoo.com / dr.assem.elnaggar@gmail.com; c: Department of Plant Production, Faculty of Agriculture (Saba-Basha), Alexandria University, Egypt. m_kadry@alexu.edu.eg / D_mahmoud aly@hotmail.com; d: Department of Floriculture and Dendrology, Hungarian University of Agriculture and Life Science (MATE), 1118 Budapest, Hungary; honfi.peter@uni-mate.hu / tillyne.mandy.andrea@uni-mate.hu /abdelhakim.eman1@gmail.com; e: Botanical Gardens Research Department, Horticulture Research Institute, Agricultural Research Center (ARC), Giza 12619 and Egypt;

* Corresponding authors: honfi.peter@uni-mate.hu (P.H); abdelhakim.eman1@gmail.com (E.A.E)

INTRODUCTION

Soil pollution with excessive quantities of heavy metals (HMs) or trace elements is a significant global environmental issue. A significant quantity of toxic HMs is added to the environment by rapid industrialization, advanced agricultural approaches, and other anthropogenic activities. These cause various hazardous impacts on all living organisms, as well as changes in soil characteristics and biological activity (Manoj et al. 2020). The release of HMs via different utilizations in industry and agriculture increases the harm to habitat and human health related to exposure to these contaminated locations and dust (Khan et al. 2010). HMs are one of the most harmful elements in the soil because of their increasing level of persistence and toxicity to living organisms (Madanan et al. 2021). The harm caused by HMs, involving adsorption and distribution through the plant cells, is affected by their bioavailability in soil and different physiological activities in plants (e.g., stage of development or plant physiological age, exposure time, HMs levels in soil, and pH of soil) (Bhargava et al. 2012). Benavides et al. (2005) and Wang et al. (2008) documented that the majority of common visual effects of HMs phytotoxicity are the decline in photosynthesis and reduction in water and nutrient absorption, disturbance in respiration and nitrogen metabolism, leaf chlorosis, and growth inhibition.

Additionally, (HMs) generate oxidative stress by producing a large amount of reactive oxygen species (ROS), which leads to cell death through the peroxidation of membrane lipids, oxidation of proteins, inhibition of enzymes, and damage to nucleic acids. To alleviate the oxidative stress, plants employ the antioxidant system via alternation in antioxidative enzyme activities such as superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase, glutathione S-transferase and guaiacol peroxidase, as well as, the level of low molecular weight antioxidants including ascorbic acid, reduced glutathione, carotenoids, phenolics (Benavides et al. 2005; Hossain et al. 2012). The equilibrium between reactive oxygen species (ROS) and the antioxidant system is advantageous for plants, as they face challenges in adapting and surviving in unfavourable situations such as heavy metal (HM) contamination (He et al. 2011; Sharma et al. 2012).

Cadmium (Cd) and lead (Pb) are well-known elements within the category of heavy metals (HMs). The industrial products containing Cd encompass paints and pigments, electroplating, plastics stabilizers, as well as the incineration of Cd-containing materials and phosphate fertilizers. At the same time, the Pb contamination sources include the emission from leaded petrol combustion, herbicides, manufacture of batteries, and pesticides (Saxena et al. 2020). A significant threat and/or toxicity can happen to plants, animals, and humans by food chain exposure of Cd and Pb, which can lodge into the ecosystem via a natural geological approach or by anthropogenic processes such as municipal and industrial wastes (Aziz et al. 2015; Sharma et al. 2023). Cadmium has stressful impacts on plants as the retardation of biomass production, soluble protein content, metabolism, enzymatic activities, and increasing ROS production (Ali et al. 2014a; Ef et al. 2015; Li et al. 2015). Also, Pb causes chlorosis, decreases seed germination, decreases plant growth and development of biomass, disturbs photosynthetic rate, reduces element and water absorption and transportation, reduces or alters membrane permeability, and generates excessive anomalous morphology and reactive oxygen species (ROS) in plants, while also inhibiting enzymatic activities in plant cells by interaction with their sulfhydryl groups (Ali et al. 2014b; Saxena et al. 2020).

Several approaches have been made to avoid the risks of HMs in polluted soil, such as contaminated site excavation and landfilling, soil flushing and washes, efficacy utilizing physiochemical techniques, and electrokinetic applications (Wuana and Okieimen 2011). Previously, Vangronsveld et al. (2009) documented that these methods are significantly costly and labor intensive, cause continuous changes in soil traits and decline of indigenous soil microflora.

One phytoremediation strategy is to discover plants that have tolerance against HMs and accumulate the MHs in their aerial organs with large biomass yield (Bhargava et al. 2012). In ideal cases, the goal is to accomplish this with no opposing impacts on growth (Ye et al. 2017). Great emphasis has been placed on the efficient application of trees in the remediation of HMs owing to their many good traits, e.g., rapid expansion combined with substantial crop output, a well-developed root system, convenient and cost-effective planting, and their aesthetically acceptable nature (Brunner et al. 2008; Luo et al. 2016).

Phytoremediation has been considered as an inexpensive option that does not require treatment or removal of the soil (Shrestha et al. 2019). Furthermore, phytoremediation enhances either physical soil characteristics or biological activities (Wan et al. 2016). Phytoremediation can be a cost-effective treatment method relative to ion substitution, solvent extraction, adsorption, oxidation-reduction, and reverse osmosis. Several studies were done on different plant species as promising candidates for the elements cadmium (Cd) and lead (Pb). Phytoremediation has been carried out using poplar species, Schima superba, Salix species, Jatropha curcas, Chinese sweetgum, and Chinese fir (Wu et al. 2010; He et al. 2011; Bhargava et al. 2012; Dai et al. 2013; Chang et al. 2014; Drzewiecka et al. 2017; El-Mahrouk et al. 2019, 2020, 2021; Wang et al. 2022).

“Several factors affect plant remediation (Wang et al. 2020). These include physiochemical soil characteristics, the exudates from plants and microbes, and the bioaccessibility of heavy metals (HMs). The effectiveness of phytoremediation also depends on the capacity of plants to assimilate, adsorb, accumulate, translocate, or sequester various toxicological aspects of metals. (Wang et al. 2020). The plants reduce the soil HMs content via different ways of phytoextraction. This involves the plants absorbing HMs from the soil and accumulating them in their aboveground portions (Sebastiani et al. 2004). Phytostabilization is a process in which certain species stabilize the soil surface by accumulating heavy metals (HMs) in their roots (Marques et al. 2009). Additionally, rhizofiltration is HMs from water, or aqueous waste streams are uptook or adsorbed by the plant roots (Erakhrumen and Agbontalor 2007)

According to Sharma et al. (2023), it is necessary to find a new species that is used as a phytoremediator of HMs and comprehend the methods by which plant species exhibit resistance to a particular metal. A promising candidate is Jacaranda mimosifolia D. Don (Fam. Bignoniaceae). It was widely planted in tropics and subtropics regions (Gentry 1992). It has soft, delicate, fernlike, deciduous foliage, and can grow to be 25 to 40 feet tall with a larger spread (Zaouchi et al. 2015; Gilman et al. 2019).

Assessing the potential of a plant to contaminate the surrounding environment through leaf shedding in any phytoremediation scenario is advantageous. Plant species, element types, and concentration in the soil affect HM levels in either green or fallen leaves. The study of Rafati et al. (2011) found that Morus alba fallen leaves contain more Cr and Ni than green leaves, but Populus alba exhibited higher concentrations of cadmium (Cd) and chromium (Cr) compared to their green counterparts. El-Mahrouk et al. (2021) supported this fact, reporting that fallen leaves from Jatropha curcas had Cd and Pb content negligible relative to the green leaves.

Most studies document the response of plants subjected to the singular stress of a heavy metal despite soil being polluted with multiple metals (He et al. 2013a,b; Chen et al. 2014). Furthermore, there is currently a lack of evidence regarding the utilization of Jacaranda mimosifolia as a phytoremediation agent for soil contaminated with cadmium (Cd) and lead (Pb) in Egypt, as well as the data about it in this aspect, are very limited in the other countries in the global. Furthermore, several regions in Egypt are contaminated with elevated levels of heavy metals (HMs), notably cadmium (Cd) and lead (Pb), stemming from the utilization of sewage effluent, industrial discharge, or drainage water in irrigation practices, as well as the application of sewage sludge as organic fertilizer for soil enrichment. Therefore, a pot experiment was conducted to get available data about the growth and efficiency of J. mimosifolia in the phytoremediation process, specifically addressing the synergistic impacts of cadmium (Cd) and lead (Pb).

EXPERIMENTAL

An experimental study in pots was carried out within the confines of Antoniadis Garden, Horticulture Research Institute, Alexandria branch, Ministry of Agriculture, Egypt, to investigate the synergistic impact of varying amounts of Cd and Pb on the development and chemical composition of Jacaranda mimosifolia during the period of 1^st April 2020 to 1^st August 2021. The goal was to study the relationship between the contents of these elements in plant parts and soil levels to estimate the phytoremediation potential and the soil properties after the plantation period.

Plant Material

A local nursery obtained one-year-old homogenous Jacaranda mimosifolia transplants (20 ± 2 cm in height).

Pollutant Treatments

Cadmium nitrate Cd (NO₃)₂ was applied at the rates of 40 [low concentration (L)], 80 [medium concentration (M)], and 120 [high concentration (H)] mg/kg soil, which was equivalent to 14.4, 28.8, and 43.2 mg of elemental Cd/kg soil. Also, lead nitrate Pb (NO₃)₂ was applied at the rates of 400 [low concentration (L)], 800 [medium concentration (M)], and 1200 [high concentration (H)] mg/kg soil, which was equivalent to 247.7, 495.4, and 743.2 mg of elemental Pb/kg soil. Plastic pots, measuring 40 cm in diameter, were filled with 9 kg of air-dried soil per pot. This soil was blended with metal solutions at the specified concentrations and kept for 60 days before being cultured outdoors under a plastic house (from 29^th January to 31^st March)—untreated soil was considered as a control. The treatments of heavy metals were conducted as follows: control, LCd LPb, MCd MPb, H Cd HPb, LCd HPb, HCd LPb, MCd HPb, and HCd MPb.

For context, world-high allowable Cd and Pb levels range from 1 to 5 and 20 to 300 mg/kg soil, respectively according to Kabata-Pendias (2011).

Transplanting Date

Similar transplants of Jacaranda mimosifolia were grown in pots filled with contaminated soil, while other pots contained untreated soil with HMs as a control (one plant/pot) on 1^st April 2020. The transplants were placed in the open field.

Experimental Layout

The subject was designed using a randomized complete block design (Snedecor 1989). The experiment contained seven applications in addition to the control (untreated soil) repeated thrice. There were three plants of each replicate, thus nine transplants for each treatment.

Agricultural Practices

Routine agricultural practices (such as weeding and the controlling of insecticides and pesticides) were done during the experimental period; Tap water (pH 7.20; EC 0.59 ds/m) was used to irrigate the plants when needed.

Measurements

On 1^st August 2021, 6 plants were randomly harvested for each utilization (2 plants of each repetition) to measure the following traits.

Vegetative Growth

Plant height (cm) and stem diameter were measured at a distance of 5 cm from the soil surface, number of branches, area/leaf (cm²) using a C1-202 Laser area meter (Cid Bio- Science, USA), software, weights of leaves, stem and roots (fresh and dry) and the longest root length (cm). The selected plants were categorized into their respective parts: roots, stems, and leaves. Subsequently, the specimens underwent two rounds of washing: first with tap water to eliminate any soil residue, and subsequently with deionized water. The plant samples were subjected to oven-drying at a temperature of 80 ˚C for a duration of 24 hours (Rautio et al. 2010). A Minolta SPAD, 502, Japan device was used to measure leaf greenness (SPAD units) (Markwell et al. 1995) in the field before harvesting the fifth leaf from the plant top.

Soil Analysis

Soil analysis was done before and after the plantation. A hydrometer was used to analyze soil physical parameters (the particle size distribution) (Gee and Bauder 1986) before the plantation only. Soil samples were collected from all repetitions for each application and then mixed carefully in one sample (Table 1). The soil air-dried samples were pulverized using a mortar and pestle and then filtered through a stainless-steel test sieve to obtain fractions smaller than 2 mm (Cools and De Vos 2010). In order to assess soil chemical characteristics, a mixture of 20 grams of dried soil and 100 milliliters of distilled water (at a ratio of 1:5) was allowed to sit for 24 h, after which the resulting extract was filtered. The recorded measurements of the soil samples were as follows: EC was measured using an EC-Meter (MI 170, Szeged, Hungary) (Jackson 1973). A volumetric Calimeter was used to determine total carbonate (Nelson and Sommers 1996).

The micro Kjeldahl method was utilized to determine the available nitrogen (N) (Bremner 1982). Available P was assessed according to Olsen et al. (1982). Ca, Mg, and Cl were also estimated (Jackson 1973). The method for measuring Na and K used a flame photometer PSP7 (JENEWY, Staffordeshire, UK) (Black 1965). The concentrations of cadmium (Cd) and lead (Pb) were determined using an atomic absorption spectrophotometer ( AAS ) (Page et al. 1982). The pH of the soil was determined by measuring the soil suspension (1:2.5, soil: distilled water) with a pH meter after a 30-minute period (JENEWY3510, Staffordeshire, UK) (Jackson 1973). For organic matter (OM) determination, 1 g of soil was blended with 10 mL of 0.1667 M K2Cr2O7 and 20 mL of concentrated H2SO4 containing 1.25% of Ag₂SO₄. The mixture was stirred, and after 30 minutes, the green color of chromium sulfate was measured using a spectrophotometer at 660 nm. Sucrose (0.42%) served as a standard, and carbon (C%) was calculated as follows:

(1)

Finally, organic matter percentage (OM%) was computed as:

(2)

Chemical Composition of Leaves, Stems, and Roots

A metal-free mill (IKa-Werke, M20 Germany) made from stainless steel was used to grind the dry samples of plant organs. 5 mL concentrated sulphuric acid was mixed with 0.2 g a homogenous powder of the plant parts, and the mixture was heated for 10 min. Then 0.5 mL of perchloric acid was added drop by drop, and the heating process was continued until a clear solution was obtained. The solution was then cooled and filtered. After that, distilled water was supplied to bring the total volume of the solution to 50 mL (Evenhuis and Dewaard 1980). The solution of samples was prepared for estimating N, P, K, and carbohydrate% in leaves (D.W), cadmium, and lead in leaves, stems, and roots (mg/kg D.W.). Also, the fallen leaves were collected during Nov. 2021, and then their Cd and Pb concentrations were determined.

Measurements of N% were obtained by the modified micro-Kjeldahl (Horwitz 1990) method, P% colorimetrically in a spectrophotometer (GT 80 + UK) (Murphy and Riley 1962), K% by flame photometer (Cottenie et al. 1982), and total carbohydrate% by (Herbert et al. 1971). Cadmium and Pb levels (mg/kg D.W.) were estimated in different plant parts using Perkin, 3300 Atomic Absorption Spectrophotometer (Page et al. 1982). The uptake of Cd or Pb was calculated as follows: Cd or Pb concentrations × D.W. (leaves, stems, and roots)/ 1000.

Total uptake = uptake of leaves +stems +roots (mg/plant) (3)

**Indicators to Determine the Efficiency of Jacaranda mimosifolia for Phytoextraction of Cd and Pb in Polluted Soil**

Bioconcentration (BCF) factor and translocation factor (TF) were calculated as follows,

(4)

(5)

where PO is the plant organ metal content (mg/kg D.W.), and SM is the soil metal content (mg/kg soil), also known as “metal level added + soil metal level before contamination”, MC is the shoots metal content (mg/kg D.W.), and MH refers to the metal content in the roots (mg/kg D.W.). TF % is used to calculate the efficiency of ion transfer from roots to aboveground plant organs (Maiti and Jaiswal 2008), where shoots refer to leaves and stems.

Accumulation efficiency was calculated based on BCF values and categorized into one of four types. The bioconcentration factor (BCF) is greater than 1 for substances with high concentration, between 1 and 0.1 for substances with medium concentration, between 0.1 and 0.01 for substances with weak concentration, and between 0.01 and 0.001 for substances that do not accumulate (Kabata-Pendias and Pendias 1999). The tolerance index biomass (TI_b) is defined as,

(6)

where TP is the treated plant D.W. (g/plant), and CP is the control plant D.W. (g/plant).

Plant D.W. referred to leaves + stems + roots.

The parameter TI_b was used to evaluate the resistance of Jacaranda mimosifolia in soil polluted with Cd and Pb, to calculate (TI_b). According to Wilkins (1978), there are 3 values: (TI_b) < 1 (a net reduction in biomass and a stressed condition of plants), TI_b = 1 (no difference comparing to treatment of control), and TI_b > 1 (a net increase in biomass and correct plant development).

The Jacaranda mimosifolia tolerance index of roots (TI_r) was also estimated (Wilkins 1978),

(7)

where AR is the length of plant roots treated with metal (cm), and LR is the control plant root length (cm).

Statistical Analysis

The data were analyzed using the SAS program (version 6.12; SAS Institute, Cary, NC). Average separation was performed using Duncan’s multiple range test using one-way ANOVA ± standard deviation (SD) (n = 3). The statistical significance was determined at a level of P ≤ 0.05.

RESULTS AND DISCUSSION

Soil Analysis

The used soil for the planting of Jacaranda mimosifolia analysis showed that the texture was sandy. The soil had an O.M of 0.53%, a pH of 8.50, and an EC level of 0.37 ds/m (Table 1). After planting, it was found that changes in the values of chemical parameters were to happen relative to prior planting and contamination; the values of pH, EC, Na ⁺, Cl ^–, HCO₃^–, and SO₄^—increased after planting. On the contrary, reductions in O.M%, CaCO₃, Ca⁺⁺, Mg^++, K⁺, and N, P, and K available levels after plantation were noticeable. Indeed, Cd and Pb levels decreased relative to their added quantities to the soil after planting. Also, the most considerable reduction in the available nitrogen, phosphorus, and potassium was to occur in the control treatment, HCd LPb, and LCd HPb, applications, each in turn after the planting. Furthermore, pH rose to 9.10 after applying MCd HPb and HCd MPb treatments. At the same time, EC value increased to 1.29 after using MCd MPb treatment.

Heavy metals application usage affected soil parameters; in this concern, some studies showed that soil characteristics including pH, O.M, and alteration capacity were more related to Cd and Pb retention (Jopony and Young 1994). The addition of metals, causing an increase in cations such as Na⁺ and anions such as Cl ^–, HCO₃^–, and SO₄^–may lead to an increase in EC value. Sharma and Raju (2013) reported that high amounts of ions and soluble salts raised EC levels in soil irrigated with industrial effluent. However, the decrease in available N, P, K, soluble cations (regardless of Na⁺), and concentrations of Cd and Pb at the ending of the trial may be due to the absorption via plant roots or the displacement by watering. Cd and Pb soil concentrations have been reduced significantly after applying phytoremediation compared to their initial levels (Durante-Yánez et al. 2022). The soil surface chemistry and metal retention are affected by pH value (Bradl 2004). Also, high pH levels lead to increased metal retention and reduced soil solubility. When the pH decreases, plant Cd uptake rises (Bolan et al. 2003). Heavy metals negatively impact microbial activities and the structure of microbial populations (Obbard 2001).

Additionally, Zhao et al. (2019) documented that metallic processes may cause alteration in the soil microenvironment, particularly HM_S precipitation. The present data were matched with those of El-Mahrouk et al. (2019), who found that EC values increased in soil polluted with CdCl₂ at 80 mg/kg soil to 5 ds/m, as well as the available N, P, K. In addition, the Cd, Cu, and Pb levels were decreased after the culture of Salix mucronata in comparison to their levels prior to planting. Also, soil characteristics, e.g., pH, CEC, and Ca levels, significantly influence on the Pb soil bioavailability (Zhang et al. 2019). Also, El-Mahrouk et al. (2020) revealed that EC increased, while the available N, P, K, and Cd, Cu, and Pb levels were reduced with a culture of Populus nigra in Cd, Cu, and Pb polluted soil. In contrast, soil pH decreased significantly under Cd stress (Wang et al. 2022).

Table 1. Soil Physiochemical Parameters before Culture and Soil Chemical Analysis as Impacted by Soil Cd and Pb Levels after Plantation of Jacaranda

Effect of HMS in Soil on Vegetative Traits

Various combinations of Cd and Pb at different concentrations significantly decreased the majority of vegetative parameters relative to their respective control (Table 2). The highest plant stature measurements (164.68 cm), stem diameter (1.36 cm), branch number (25.33/plant), and area/leaf (205.57 cm²) were produced from the negative control group. In addition, the control plants had the maximum fresh and dried weights of leaves (53.44 and 26.27 g/plant), stems (126.01 and 47.57 g/plant), and roots (106.67 and 52.59 g/plant), respectively. The non-treated control reported higher values of the longest root and greenness degrees as 55.67 cm and 36.73 SPSD units in succession. In contrast, HCd HPb treatment had the most negative impact on the traits mentioned above.

The reduction in vegetative traits after applying HCd HPb reached 28% in plant height, 13% in stem diameter, 41% in branch number, 35% in area/ leaf, 34 and 30%, 49 and 41%, and 64 and 55% in leaves, stems, and roots fresh and dry weights, consecutively, 39% in the longest root length, and 26% in SPAD units. It is noticed from the data that some Cd and Pb combinations had a significant impact similar to their respective controls on some vegetative parameters. Also, the effects on vegetative traits of some treatments used were insignificant (P ≤ 0.05) among themselves, regardless of the control treatments. Despite the negative influence of Cd and Pb combinations, particularly at high concentrations, the Jacaranda plants could tolerate and grow with 100% survival in all the used treatments.

Surely, the detrimental impacts of Cd and Pb treatments on soil parameters conversely affected vegetative growth. Some harmful influences were noticed on the aged leaves, e.g., leaf edges exhibiting yellow discoloration and desiccation under treatments of high HM_S levels. The toxicity symptoms were reduced with increasing plant age. Accordingly, Tu et al. (2004) mentioned that tolerance raised by the increment in plant age and some visual harm was reduced in aged Pteris vittata. This means that Jacaranda could grow in Cd- and Pb-rich environments. The previous studies indicated that growth reduction and leaves abscission in willow tangio (S. mastudana x S. alba) resulted from the application of 0.6 to 60.6 µg Cd/g soil (Robinson et al. 2000). Also, despite the retardation impacts on the growth traits related to soil Cd and Pb at high concentrations, Populus maximowiczii x P. nigra has the ability to thrive in 7.3 and 1368 mg Cd and Pb/kg soil, respectively (Kubátová et al. 2016). Conversely, the used HM_S levels negatively affected all vegetative traits, and the inhibition impact was correlated with the HM concentration and growth traits. Dong et al. (2005) documented that Cd stress causes deleterious effects on the level of photosynthesis and CO₂ level through cells and involves photosynthetic pigments via Cd⁺⁺ replacing Mg₂⁺in chlorophyll structure, resulting in more decrease in fluorescence quantity in comparison to Mg chlorophylls. The two harmful impacts decrease the chlorophyll yield, reducing the photosynthetic rate that leads to aging and cellular demise (Santos et al. 2010). In addition, plant physiological and biochemical prosses have been deleterious and affected by cadmium (Cd) absorption and retention in plants (Li et al. 2023). Similarly, Zacchini et al. (2009) found that 38.5 mg/L Cd sulfate negatively affected the willow clone’s total leaf area. The study conducted by Tauqeer et al. (2016) found that the presence of Cd at a concentration of 0.225 mg/L and Pb at a concentration of 0.414 mg/L resulted in a significant decrease in the fresh and dry weights of Alternanthera bettzickiana. Additionally, Pb harm causes photosynthesis reduction, oxidative hazard, DNA harm, and undesirable in mitosis (Küpper 2017). The findings of the present study are consistent with the research conducted by Redovniković et al. (2017), which showed that different combinations of Cd (10, 25, and 50 mg/kg soil) and Pb (400, 800, and 1200 mg/kg soil) negatively affected leaves, stem, and root dry weights of P. nigra “Italica”, and the most negative effect was to be found at the combination of Cd and Pb at high levels. Similarly, El-Mahrouk et al. (2021), studying Jatropha curcas, found that Cd at 14.4, 28.8, and 43.2 mg/kg soil and Pb at 247.7, 495.4, and 743.2 mg/kg soil in different combinations negatively affected vegetative traits in relative to untreated negative plants. In addition, El-Mahrouk et al. (2019, 2020), studying Salix mucronata and Populus nigra, respectively, concluded that Cd at 3.9, 7.8, 11.9, and 15.6 mg/kg soil, Cu at 14.4, 29.8, 47.7, and 63.6 mg/kg soil, and Pb at 50.0, 91.1, 132.1, and 173.3 mg/kg soil had significantly inhibition influences on the aerial organs and root traits of the two species, and the negative impact was parallel with the HM concentration in the soil. The retardation in root growth and element and water uptake imbalance causes development reduction, structure harmful, reduction in biochemical and physiological processes, which influence on biomass yield negatively (Kumar et al. 2017; Wu et al. 2018). Also, the root, stem, leaf, and dry biomass of Clidemia sericea showed a decrease under Hg, Cd, and Pb stresses (Durante-Yánez et al. 2022). Furthermore, growth inhibition of Schima superba, Chinese sweetgum, and Chinese fir was presented at 6, 12, 24, and 36 mg Cd/kg soil (Wang et al. 2022). Additionally, Bhat et al. (2022) reported that a maximum reduction in the growth rate of Spirodela polyrhiza treated with Cu, Pb, and Cd at 0, 0.5, 1, 2, 4, and 8 mg was noticed in treatments of Cd, followed by Pb, then Cu. They added that the highest photosynthetic pigment levels were observed in control plants (untreated). In addition, photosynthetic pigment contents have been differently affected depending on plant species, potentially toxic element levels, and the toxicity degree of metals individually and mixed according to the studies of Fargašová and Molnárová (2010) on Sinaps alba, Chinmayee et al. (2012) on Amaranthus spinosus, Leal-Alvarado et al. (2016) on Salvinia minima Baker, and Zhang et al. (2020) on tobacco. Zhang et al. (2020) documented that HM_S such as Cr, Ni, Pb, Cd and Zn affected species growth. The reduction in vegetative traits of Jacaranda can be attributed to the detrimental impact of Cd and Pb on leaf chemical composition because N, P, and K elements are essential to several compounds, e.g., proteins, carbohydrates, amino acids, phospholipids, nucleic acids, and energy sources. Furthermore, the presence of cadmium (Cd) and lead (Pb) exerts a detrimental impact on the plasma membrane permeability (Sharma et al. 2010; Pourrut et al. 2011).

Table 2. Growth Traits of Jacaranda as Impacted by Cd and Pb Levels in the Soil after the Experimental Period

Leaf Chemical Analysis

It is necessary to determine leaf N, P, and K nutrient levels because because the soil pH in which Jacaranda was grown increased after contamination of Cd and Pb metals from pH 8.5 to 9.1. This pH implied that the absorption of the vital elements via plant roots, particularly N, P, K, Mg, and Zn, is not enough. Our results indicated that Jacaranda grown in HMS polluted soil had significantly lower amounts of N, P, K, and total carbohydrates percentages than respective controls (Table 3), with some exceptions. Meanwhile, MCd MPb, LCd HPb, and MCd HPb treatments resulted in a non-significant lower P% compared to the control. Additionally, the applications of LCd LPb, MCd MPb, and HCd MPb recorded the same significant level of K% of control. Distinctly, leaf N, P, K, and total carbohydrate status depend on the concentration of HM in the application. This may be due to the synergistic effect of each HM used. Furtherance, lower significant levels of N, P, K, and total carbohydrates % were exhibited in HCd HPb treated plants. Such a treatment decreased N, P, K, and total carbohydrates by 25.35, 64.30, 32.26, and 19.89%, respectively, less than the control.

Foliage nutrient levels depend on soil or soil chemistry levels and the consanguinity of Salix species or clones (Mosseler and Major 2017). Heavy metals lead to hazards in plants via (i) an obstacle for uptake at root surface as a result to similarities with nutrient cations, like the competition between AS and P and Cd against Zn, (ii) a function collapse of necessary nutrients because of vital cations exclusion from their binding sites (Sharma and Dietz 2009; DalCorso et al. 2013). Also, reducing absorptions and transference of nitrate and nitrate reductase by Cd affect N metabolism (Lea and Miflin 2003).

Moreover, Küpper et al. (1996) documented that magnesium in the antenna and efficacy centers of chlorophyll can be substituted by Cu , which affects the composition and function of chlorophyll, causing a decrease in build-up carbohydrate. Moreover, the ADP or ATP phosphate group displaced by vital ions were reacted by Pb accumulation in the plant tissue, thus weakening essential nutrient uptake like Mg and Fe, and inducing CO₂ retardation because of stomatal closure (Pourrut et al. 2011). Previously, Pietrini et al. (2009) cleared various nutrients (e.g., Fe, Zn, and Mg); their uptake, transport, and use in poplar clones were negatively affected by Cd SO₄ at 50 µM. Also, Cd impairs the Calvin cycle enzymes, photosynthetic rate, and metabolism of carbohydrates (Tang et al. 2017) and changes the metabolism of antioxidants (Khan et al. 2009). Cadmium also is an obstacle to the absorption of Ca, K, P, Mg, and water and retards nitrate transportation and uptake by affecting nitrate reductase. Likewise, El-Mahrouk et al. (2019) on Salix mucronata and El-Mahrouk et al. (2020) on Populus nigra reported that leaf N, P, K, and total carbohydrates of two species significantly reduced Cd CL2 at 20, 40, 60, and 80, respectively, and Pb acetate at 250, 450, 600, and 850 mg/kg soil, respectively, relative to the control.

Table 3. Effect of Soil Cd and Pb Levels on the Chemical Composition of Jacaranda Leaves Following the Experiment Period

Means± (SD) (n = 3) with the same letters in a column are non-significant differences (P≤ 0.05) according to Duncan’s multiple range test.

Relationship between Cd and Pb Levels and Uptake in Plant Organs and their Soil Concentrations

The results in Table 4 show that the used Cd and Pb combinations were significantly elevated (P≤ 0.05) in leaves (green leaf and fallen leaf), stems, and roots Cd and Pb contents and uptake, as well as in plant total absorption relative to control untreated plants. Also, the Cd and Pb levels of different plant parts strongly depend on their soil levels. Further, combinations containing high Cd levels (HCd HPb, HCd LPb, and HCd MPb) recorded higher leaf, stem, and root Cd concentrations than the other treatments. This was found in Pb content in the plant parts, where HCd HPb, LCd HPb, and MCd HPb combinations resulted in higher Pb content. Data indicated that contents of Cd and Pb were in the order of roots ˃ stems ˃, and leaves under the most treatments.

Moreover, Cd or Pb transfer in various vegetative parts and total plant absorption were found to be dependent on their soil contents and plant organs. Higher significant Cd uptake in leaves stems, and roots resulted from applying HCd MPb treatment, besides HCd LPb treatment in the case of root uptake. Higher significant leaf, stem, and root Pb uptake was recorded for MCd and HPb treatment besides HCd and MPb in the case of root uptake. At the same time, total Cd and Pb plant uptake was significantly the highest at HCd MPb treatment (0.44 mg Cd/ plant) and MCd HPb (7.50 mg Pb/ plant), respectively. Generally, Cd and Pb uptake was in an order of roots > stem > leaves. The results indicated that the Cd and Pd contents of fallen leaves were negligible relative to their contents in the green leaves under the all-tested Cd and Pb combinations. The maximum significant content of Cd and Pb in the fallen leaves reached 0.03 (for the treatment content of high Cd level) and 0.08 (for the treatment of LCd HPb) mg/kg D.W. against 3.30 (HCd HPb) and 45.70 (MCd HPb) mg/kg D.W. in the green leaves, respectively.

As for Cd and Pb content and uptake in the plant organs, Samuilov et al. (2016) mentioned that Pb concentrations in Populus tremula x P. alba vegetative parts are conjunctive with their content in the soil. Previously, Zhivotovsky et al. (2011) documented that Cd and Pb accumulated in roots of several tree species more than in stems and leaves. Redovniković et al. (2017) reported that Cd and Pb accumulated in roots of P. nigra cv. ‘Italica’ rather than in leaves and stem when grown in Cd at 10, 25, and 50 mg/kg soil and Pb at 400, 800, and 1200 mg/kg soil. Likewise, Krajcarová et al. (2016) showed that when treated with Cd, Salix polaris plant parts have different Cd concentrations. In studies of Tang et al. (2017) on Salix matsudana, Pb in all vegetative organs was in an order of roots ˃ cuttings ˃ twigs ˃ leaves. Additionally, roots of S. mucronata and P. nigra have Cd and Pb content and uptake more than in stems or leaves (El-Mahrouk et al. 2019, 2020) of Salix and poplar, respectively. In addition, Durante-Yánez et al. (2022) documented that the levels of Hg, Pb, and Cd in roots, stem, and leaves of Clidemia sericea indicated significant differences among the used treatments, and the roots had higher concentrations than leaves or stems. According to Tatian et al. (2023), Cd and Pb uptake by Festuca species was mainly in the roots rather than aerial parts. Also, Bhat et al. (2022) treated Spirodela polyrhiza with Cu, Pb, and Cd at 0, 1, 2, 4, and 8 mg/L and they reported that elements levels in the plant was influenced by its behavior. The plant’s ability to accumulate these metals was directly related to the concentration of the metals in the soil, with higher concentrations leading to increased uptake by the plant. Furthermore, accumulation of HM_S in the plant organs related to HM kind and plant variety. Accordingly, Rahman et al. (2022) revealed that the seasonal HM_S contents in either leaves or bark of some tree species decreased in the order of Zn ˃ Pb ˃ Cu ˃ Cd in the industrial and residential areas. They added that the tree species markedly showed significantly various capacities for HM accumulation. Cadmium and lead contents in fallen leaves were negligible. That may be due to Cd and Pb transported from leaves to stem and root at the senescence stage. Also, the root of Jacaranda had more accumulation of Cd and Pb than the leaves or stems. Hence, the potential environmental hazard posed from falling leaves appears to be minimal, as proposed by Baker (1981), pointing out that a number of species of deciduous plants move the stored HMS to their aerial parts prior to senescence. In addition, willow stand (Salix viminalis L. ‘Orm’) reduces the pollution hazardous to the wider habitat within leaf fall when they do not accumulate HM_S in their leaves (Vervaeke et al. 2003).

Also, the green leaves of Morus alba grown in 40 mg Cd/kg soil had higher content of Cd than fallen leaves; in contrast, fallen leaves had more Cr in a level of 60 mg/kg soil and Ni in a level of 1200 mg/kg soil than the green leaves (Rafati et al. 2011). They added that green and fallen leaves of P. alba Cd uptake levels did not significantly differ when treated with 40, 80, and 120 mg Cd/kg soil because green leaves occupied their Cd uptake until the fall season. This means that built-up Cd did not undergo translocation into the stem and root structures. Additionally, Jatropha curcas grown under 40, 80, and 120 mg Cd nitrate/kg soil and Pb nitrate at 400, 800, and 1200 mg/kg soil in various combinations, the green leaves had a considerable amount of Cd and Pb more than fallen leaves in all used combinations ( El-Mahrouk et al. 2021).

Table 4. Effect of the Different Cd and Pb Combinations on their Concentrations and Absorptions in Various Plant organs, and Plant Total Uptake