Acta agriculturae Slovenica, 121/4, 1–10, Ljubljana 2025 doi:10.14720/aas.2025.121.4.22996 Original research article / izvirni znanstveni članek Silicon as a potential bioremediation agent for mitigating aluminum toxic- ity in aquatic microalgae: Implications for sustainable agricultural ecosys- tems Ghozlene ISSAAD 1, 2, Mounia AOUISSI 3, 4, Hocine FREHI 3, Houria BERREBBAH 1, Mohamed Reda DJEBAR 5 Received August 03, 2025, accepted November 19, 2025 Delo je prispelo 3. avgust 2025, sprejeto 19. november 2025 1 Laboartory of cell Toxicology, Department of Biology, Faculty of Sciences, Badji-Mokhtar University of Annaba, Algeria. 2 Correspondence: ghozlenebougerra@gmail.com 3 Laboratory of Murine Biology, Department of Biology, Faculty of Sciences, Badji-Mokhtar University of Annaba, Algeria. 4 Department of Biological Sciences, Faculty of Natural Sciences and Life, University of Souk Ahras, Algeria 5 Environmental Research Center, Alzone Menadia, Annaba 23000, Algeria Silicon as a potential bioremediation agent for mitigating alu- minum toxicity in aquatic microalgae: Implications for sus- tainable agricultural ecosystems Abstract: Heavy metal pollution in agricultural and aquatic ecosystems seriously affect microorganisms essential for ecological balance. Microalgae, as primary producers, are particularly vulnerable to such contaminants while being vital components of sustainable agricultural systems. In this study, we conducted a controlled laboratory experiment to evaluate and compare the specific impacts of silicon (Si) and aluminium (Al) exposure on the growth, biomass, chlorophyll content, and morphology of three economically important microalgae spe- cies: Chlorella vulgaris, Haematococcus pluvialis, and Tetrasel- mis suecica. Cultures were exposed to varying concentrations of aluminium (1, 10, and 100 mg l-1) and silicon (100, 150, and 200 mg l-1) for three weeks under controlled conditions. Results demonstrated that aluminium caused a significant, concentra- tion-dependent inhibition of growth (37–62 %), reduced total chlorophyll content, and induced morphological alterations such as cell swelling and chlorophyll degradation. Conversely, silicon treatment not only showed minimal adverse effects but also exhibited a partial protective role by maintaining higher growth and chlorophyll levels compared to Al-exposed groups. These findings clearly indicate that silicon can mitigate alu- minium toxicity in microalgae, enhancing their resilience un- der metal stress. While not directly applicable to higher plants, these findings offer insight into microbial metalloid interac- tions relevant to Si-mediated crop protection. Key words: silicon, aluminium toxicity, microalgae physi- ology, aquatic ecosystems, agricultural water quality. Silicij kot potencialno bioremediacijsko sredstvo za ublažitev toksičnosti aluminija v vodnih mikroalgah: Posledice za traj- nostne kmetijske ekosisteme Izvleček: Onesnaženje s težkimi kovinami v kmetijskih in vodnih ekosistemih močno ogroža mikroorganizme, ki so bist- veni za ekološko ravnovesje. Mikroalge kot primarni proizva- jalci so še posebej občutljive na takšne onesnaževalce, medtem ko so bistvene sestavine trajnostnih kmetijskih sistemov. V tej raziskavi so izvedli nadzorovan laboratorijski poskus, da bi ocenili in primerjali posebne vplive izpostavljenosti siliciju (Si) in aluminiju (Al) na rast, biomaso, vsebnost klorofila in mor- fologijo treh gospodarsko pomembnih vrst mikroalg: Chlo- rella vulgaris, Haematococcus pluvialis in Tetraselmis suecica. Kulture so bile tri tedne v nadzorovanih razmerah izpostav- ljene različnim koncentracijam aluminija (1, 10 in 100 mg l-1) in silicija (100, 150 in 200 mg l-1). Rezultati so pokazali, da je aluminij povzročil pomembno, od koncentracije odvisno za- viranje rasti (37–62 %), zmanjšal skupno vsebnost klorofila in povzročil morfološke spremembe, kot sta nabrekanje celic in razgradnja klorofila. Nasprotno pa obravnavanje s silicijem ni pokazalo le minimalnih škodljivih učinkov, ampak tudi delno zaščitno vlogo z ohranjanjem večje rasti in večje vsebnosti klorofila v primerjavi s skupinami, izpostavljenimi Al. Te ugo- tovitve jasno kažejo, da lahko silicij ublaži toksičnost aluminija v mikroalgah in poveča njihovo odpornost na obremenitev s kovinami. Čeprav te ugotovitve niso neposredno uporabne za višje rastline, ponujajo vpogled v interakcije mikrobnih met- aloidov, ki so pomembne za zaščito pridelka, posredovano s Si. Ključne besede: silicij, toksičnost aluminija, fiziologija mikroalg, vodni ekosistemi, kakovost kmetijske vode. Acta agriculturae Slovenica, 121/4 – 20252 G. ISSAAD et al. 1 INTRODUCTION Microalgae are fundamental components of aquatic ecosystems and have gained significant attention for their diverse applications in sustainable agriculture, biofuel production, wastewater treatment, and pharmaceutical products (Grönlund et al., 2004). As primary producers in agricultural watersheds and irrigation systems, micro- algae contribute to nutrient cycling and are bioindicators of environmental health. However, their growth and bio- chemical composition are increasingly threatened by en- vironmental stressors, particularly in agricultural land- scapes where runoff can introduce various contaminants into aquatic systems. Heavy metals and metalloids from agricultural inputs and industrial activities have emerged as significant threats to microalgal communities. Silicon (Si) and aluminium (Al) are ubiquitous elements in ag- ricultural soils and water systems that can accumulate in aquatic environments, potentially influencing the physi- ology and productivity of microalgae, and thus impact- ing the ecological functions of agricultural water sys- tems (Quiroz-Vazquez et al., 2008). Silicon, a beneficial element for many plants including agricultural crops, has been recognized for its positive effects on cell wall formation, mechanical stability, and overall growth en- hancement in various microalgae (Martin-Jézéquel et al., 2000). This element also plays a crucial role in mitigating biotic and abiotic stresses in crop plants, suggesting po- tential similar protective functions in microalgae under conditions of metal stress. Conversely, aluminium, while naturally abundant in agricultural soils, can exert toxic effects on microorganisms due to its ability to interfere with cellular processes and enzyme activities (Trenfield et al., 2015). Aluminium toxicity is a significant con- straint in acidic soils worldwide, affecting approximately 40 % of arable lands and causing substantial yield reduc- tions in sensitive crops. Understanding Al toxicity mech- anisms in microalgae may provide insights into related processes in higher plants and guide strategies for main- taining healthy microalgal populations in agricultural water systems. Chlorella vulgaris Beijerinck, Haemato- coccus pluvialis Flotow, and Tetraselmis suecica (Kylin) Butcher are three widely studied microalgal species with diverse ecological roles and agricultural applications, including as biofertilizers, soil conditioners, and com- ponents of integrated farming systems. While extensive research has examined the physiological responses of these microalgae to various stressors (Ciccia et al., 2023), the specific effects of Si supplementation and Al toxicity on their growth and chlorophyll content in agricultural water contexts have not been comprehensively explored. Chlorophyll content and growth are among the most characteristic indicators of heavy metal stress in photo- synthetic organisms, with toxicity causing alterations in chloroplast and cell membrane structure (Stoeva et al., 2005). These parameters serve as valuable metrics for as- sessing the impact of contaminants on photosynthetic efficiency and biomass production, which ultimately in- fluence ecosystem functionality and water quality in ag- ricultural systems. Although the protective role of Si has been documented in higher plants, the current study fo- cuses exclusively on microalgae. Thus, while the findings may suggest potential strategies for mitigating Al toxicity in crops, direct extrapolation to plants requires further investigation. This research aims to compare the impacts of Si supplementation and Al toxicity on the growth, biomass, chlorophyll content, and morphology of C. vul- garis, H. pluvialis, and T. suecica within the context of ag- ricultural water systems. The findings are anticipated to contribute to the development of strategies for mitigating the adverse effects of metal contamination on microal- gal communities in agricultural watersheds, thereby pre- serving their ecological functions while potentially of- fering insights into crop protection mechanisms against Al toxicity. Additionally, this research may inform sus- tainable water management practices in agriculture and forestry, where understanding metalloid interactions is crucial for maintaining ecosystem health, productivity, and water quality. 2 MATERIALS AND METHODS 2.1 MICROALGA STRAINS AND CULTURE The three species of microalgae, Chlorella vulgaris, Haematococcus pluvialis, and Tetraselmis suecica obtained from the French Culture Collection of Algae (Termar) were cultivated in sterilized blue-green medium (BG-11) supplemented with vitamins (B1, and B12) as previously described (Bischoff, 1963). The algae cells were incubat- ed in a phytotron room maintained at a temperature of 26 °C and a photoperiod of a 12 hour light/12 hour dark cycle. The microalgae were grown in 250 ml Erlenmeyer flasks containing 150 ml of the liquid BG-11 medium to reach an initial algal cell density of 1 × 106 cells ml-1 prior to the experiment (day 0). 2.2 TREATMENT The three growing microalgae strains, Chlorella vul- garis, Haematococcus pluvialis, and Tetraselmis suecica, were separately exposed to increasing concentrations of aluminum chloride hexahydrate (Sigma-Aldrich, CAS #: 7784-13-6); 0, 1, 10, and 100 mg  l-1, and silicon (SiO2, Acta agriculturae Slovenica, 121/4 – 2025 3 Silicon as a potential bioremediation agent for mitigating aluminum toxicity in aquatic microalgae: ... sustainable agricultural ecosystems Sigma-Aldrich, 99.9 %); 0, 100, 150, and 200 mg l-1, for 7, 14, and 21 days. The selected testing concentrations were chosen based on a preliminary test study conducted on these algal cells using various concentrations. 2.3 DETERMINATION OF DRY BIOMASS AND TOTAL CHLOROPHYLL CONTENT The dry biomass content in the three strains was determined according to a previously reported pro- tocol (Zhu & Lee, 1997). In brief, 5 ml from each mi- croalgae sample was washed with distilled water, fil- tered on Whatman glass microfiber filters (1825-055) that were previously dried and weighed, and then heated in the oven at 105  °C for 1 hour, then weighed again. The total chlorophyll content of each microalgae strain, treated separately with Al or Si, was determined at different time intervals (7, 14, and 21 days), as reported elsewhere (Porra et al., 1989)”type”:”article- jour na l”,”volume” :”975”} ,”ur is” : [“http : / /w w w. m e n d e l e y. c om / d o c u m e nt s / ? uu i d = b 5 9 9 7 d 3 7 - 49d0-42b3-9463-2942431674bf ”,”http://www.men- dele y.com/do cuments/?uuid=d01d457e-5b1e- 40ff-855c-1b3f863ec798”,”http://www.mendeley. com/documents/?uuid=6e3f721c-ea2d-4d4f-851a- 947255397f96”]}],”mendeley”:{“formattedCitation”:”(Po rra et al., 1989. Briefly, 0.05 g of freeze-dried microalgae was mixed with 8 ml of acetone solution (80% (v/v) and 2.5 mM sodium phosphate buffer, pH 7.8) for 16 hours. After that, samples were centrifuged at 2,000  ×  g for 2 minutes, the supernatant was removed, and the algal cell pellet was washed with 2 ml of acetone, centrifuged twice, and the acetone fractions were pooled. The final volume was adjusted to 15 ml with acetone. The chloro- phyll absorbance was determined using a UV–Vis spec- trophotometer (Thermo-Scientific, USA), and the total chlorophyll content was calculated using the following equation. 2.4 DETERMINATION OF CELL GROWTH INHI- BITION Cell growth inhibition of control cells and those treated with aluminum and silicon was determined based on the calculation of the rate of cell growth. The inhibition percentage (I %) at each concentration of each chemical was calculated as follows: Where μ is the mean value for the average specific growth rate in control test algal cells and μ is the average specific growth rate for the treatment replicates. 2.5 MORPHOLOGICAL EVALUATION Morphological changes in the tested microalgae were exam- ined using a light microscope (Carl Zeiss, Germany) at 40  × magnification, equipped with a digital camera (AxioCam ICc 3) connected to a computer. Image capture and size analysis were performed using AxioVision software (version 4.8.2.0, Carl Zeiss). Representative micrographs were obtained from three independent cultures, with a scale bar of 20 µm included in the figures. 2.6 STATISTICAL ANALYSIS All experiments were performed at least three times, and data are expressed as mean ± SD. Statistical analysis was carried out using one-way ANOVA followed by Tuk- ey’s post hoc test (GraphPad Prism Software) to compare treatment groups with the control. Differences were con- sidered statistically significant at p ≤ 0.05, denoted as *p < 0.05, **p<0.01, and ***p < 0.001 versus control 3 RESULTS AND DISCUSSION 3.1 DRY BIOMASS AND TOTAL CHLOROPHYLL CONTENT As shown in Figure 1, aluminium and silicon treat- ments significantly increased biomass in all three algal species in a concentration- and time-dependent manner, while silicon treatment produced smaller but statistically significant increases in several comparisons versus con- trol. In Chlorella vulgaris, biomass was increased mark- edly by all Al concentrations (p <0.01 at day 7; p < 0.001 at day 14 and 21). Si treatments caused less pronounced but significant increases at some time points (typically p < 0.05). In Haematococcus ., Al 100 mg  l-1 increased biomass from day 7 onward (p < 0.01 at days 7 and 14; p < 0.001 at day 21), and Al 1 and 10 mg  l-1 produced modest increases (p < 0.05 at days 7; p < 0.01 at day 14; and p < 0.001 at day 21). Si treatments produced small but significant increases in a subset of comparisons (*p < 0.05). In Tetraselmis ., all Al treatments increased bio- mass (p < 0.01 at all time points), and Si treatments again Acta agriculturae Slovenica, 121/4 – 20254 G. ISSAAD et al. yielded milder yet significant increases (p < 0.05). Collec- tively, Al treatment, particularly at 100 mg l-1 produced the largest increases in biomass across species, while Si treatment produced modest but statistically significant increases in several instances. The observed biomass in- crease under Al stress may reflect hormesis, where low levels of stressors stimulate compensatory biological responses that enhance growth (Kaur et al., 2024; Zhou et al., 2024). Similar hormetic responses have been re- ported in Chromochloris zofingiensis (Dönz) Fucíková & L.A.Lewis exposed to cadmium, where sub-lethal stress enhanced biomass production (Y. Zhang et al., 2024). Moreover, recent studies show that hormetic responses are not limited to heavy metals, as nanomaterial-induced stress can also increase microalgal biomass and photo- synthetic efficiency under specific conditions (Hidalgo et al., 2023). Silicon supplementation further supports growth by mitigating oxidative stress and modulating antioxidant enzyme activities, consistent with its role in higher plants, where it stabilizes cell walls, alleviates metal toxicity, and enhances stress resilience (Denarié et al., 2025; Ma & Naoki Yamaji, 2015; Saleem et al., 2025; Wanas et al., 2025). Previous studies mainly focused on Al toxicity without evaluating protective agents like Si. Our findings indicate that microalgae can exhibit both adaptive and hormetic responses to metal stress, and Si supplementation may enhance biomass production and stress tolerance, offering potential for biotechnological applications (Cavalletti et al., 2025; Ding, 2025). In Figure 2, aluminium treatment generally decreased to- tal chlorophyll content in all three algal species, whereas silicon treatment had little to no significant effect com- pared with the control. In Chlorella v., Al treatments sig- nificantly reduced chlorophyll levels for all Al concentra- tions vs. control (p < 0.01 at day 7, p < 0.001 at days 14 and 21), while Si treatments showed no significant differ- ence (ns). In Haematococcus p., Al treatments decreased chlorophyll all Al concentrations and treatment exposure time vs. control (**p < 0.01), with no effect observed for Si (ns). In Tetraselmis s., the same overall pattern was ob- served: Al decreased chlorophyll content significantly at day 7 (**p < 0.01), days 14 and 21 (p < 0.001), while Si Figure 1: Dry biomass of Chlorella vulgaris, Haematococcus pluvialis, and Tetraselmis suecica exposed to aluminium (Al; 1, 10, and 100 mg l-1) and silicon (Si; 100, 150, and 200 mg l-1) for 7, 14, and 21 days. Values are presented as mean ± SD (n = 3 independent cultures per species). Different letters above bars indicate statistically significant differences between treatments at each time point (p < 0.05). Acta agriculturae Slovenica, 121/4 – 2025 5 Silicon as a potential bioremediation agent for mitigating aluminum toxicity in aquatic microalgae: ... sustainable agricultural ecosystems treatments showed no significant differences from the control at any time point. Collectively, these findings indicate that Al treatment consistently and significantly decreased total chlorophyll content in all three algal spe- cies, with the strongest reductions observed at higher concentrations and later time points, whereas Si treat- ment produced no measurable effects. It is important to note that microalgae and higher plants differ consider- ably in physiology and uptake pathways, so direct ex- trapolation to cultivated plants should be done with cau- tion. Aluminium is known to induce oxidative toxicity in some microalgae species (Jeffrey & Haxo, 1968), whereas silicon can be beneficial even at higher concentrations (Hou et al., 2023; Zhang et al., 2023). Consistently, this study revealed a marked increase in dry biomass under Al stress, aligning with recent findings (Kaur et al., 2024; Yang et al., 2023). The observed chlorophyll reduction under Al stress is consistent with reports that heavy met- als inhibit chlorophyll biosynthesis and promote degra- dation via oxidative stress (Rao et al., 2025; Sharma et al., 2025). Conversely, Si supplementation alleviates metal- induced chlorophyll loss by enhancing antioxidant de- fenses and stabilizing chloroplast membranes, thereby preserving photosynthetic capacity (Manimaranet al., 2015; Monteiro, 2022). These protective effects help maintain photosynthetic efficiency and support growth under stress conditions. 3.2 CELL GROWTH INHIBITION Figure 3 illustrates that aluminium (Al) exposure significantly inhibited algal growth in a concentration- and time-dependent manner. After 7 days of exposure, Al concentrations of 1, 10, and 100 mg  l-1 resulted in growth inhibition of 37 %, 46 %, and 59 % in Chlorella vulgaris and Haematococcus pluvialis, respectively. In contrast, Tetraselmis suecica exhibited higher sensitivity, with growth inhibitions of 49 %, 55 %, and 62 % under the same Al concentrations. These findings are consistent with previous reports showing concentration-dependent inhibition of Chlorella and Scenedesmus growth by Al₂O₃ nanoparticles (72-h EC₅₀ ≈ 45 mg  l-1 and 39 mg  l-1, re- spectively) (Sadiq et al., 2011), as well as long-term in- Figure 2: Total chlorophyll content in Chlorella vulgaris, Haematococcus pluvialis, and Tetraselmis suecica exposed to aluminium (Al; 1, 10, and 100 mg l-1) and silicon (Si; 100, 150, and 200 mg l-1) for 7, 14, and 21 days. Values are mean ± SD (n = 3 independent cultures per species). Different letters indicate statistically significant differences compared with the control (p < 0.05). Acta agriculturae Slovenica, 121/4 – 20256 G. ISSAAD et al. hibition (20–40  %) of Scenedesmus armatus (Chodat) Chodat growth under Al nanoparticle exposure(Cortés- Téllez et al., 2024). Similar reductions in chlorophyll con- tent and photosynthetic performance were also docu- mented in Dunaliella salina (Dunal) Teodoresco exposed to Al₂O₃ nanoparticles (Shirazi et al., 2015). These find- ings suggest that C. vulgaris is the most susceptible spe- cies to Al-induced growth inhibition among the tested microalgae. Conversely, silicon (Si) treatment led to only modest and statistically insignificant growth reductions (~15 %, 19 %, and 23 % across the three strains) after 7 days. Notably, this inhibitory effect diminished with pro- longed exposure periods, indicating a potential acclima- tion or reduced bioavailability of Si over time. However, the efficacy of Si in mitigating Al-induced toxicity in mi- croalgae does not necessarily extrapolate to crop plants. Further experimental validation under field-relevant Figure 3: Growth inhibition (%) in Chlorella vulgaris, Haematococcus pluvialis, and Tetraselmis suecica exposed to aluminium (Al; 1, 10, and 100 mg l-1) and silicon (Si; 100, 150, and 200 ) for 7, 14, and 21 days. Values are mean ± SD (n = 3 independent cultures per species). Different letters indicate statistically significant differences compared with the control (p < 0.05). agricultural conditions is imperative. Importantly, com- parable Si-mediated alleviation of Al toxicity has been reported in higher plants, including upland rice (where Si reduced Al translocation to shoots) (Munyaneza et al., 2024), Eucalyptus platyphylla F.Muell. (Si decreased ROS accumulation and improved pigments and gas exchange) (Lima et al., 2016), Tartary buckwheat (enhanced anti- oxidant defenses) (Qi et al., 2024), and maize exposed to SiO₂ nanoparticles (increased detoxification and an- tioxidative activity) (De Sousa et al., 2019). These studies support the hypothesis that Si supplementation confers cross-kingdom protection against Al toxicity. The inhibi- tory effects of Al and Al-based nanoparticles (nanoAl) on algal growth have been extensively documented (Das et al., 2023; Gebara et al., 2023; Nurhidayati et al., 2023), further corroborating the detrimental impacts on algal biomass and photosynthetic efficiency. In con- Acta agriculturae Slovenica, 121/4 – 2025 7 Silicon as a potential bioremediation agent for mitigating aluminum toxicity in aquatic microalgae: ... sustainable agricultural ecosystems trast, Si and Si-based nanoparticles have been reported to exhibit minimal toxicity to algal cells. For instance, a negligible growth inhibition was reported in Chlorella vulgaris upon exposure to SiO₂ nanoparticles (Ahmed et al., 2023; Maia et al., 2024; Yadav et al., 2023). Simi- larly, no adverse effect on algal growth was reported in Si treatments, suggesting a potential role for Si in alleviat- ing metal-induced stress in microalgae (Ghariani et al., 2025; Manimaran et al., 2015). Molecular and biochemi- cal analyses have elucidated the mechanisms underlying Al-induced growth inhibition in microalgae. Alterations in photosynthetic pigment content, reactive oxygen spe- cies (ROS) accumulation, and enzyme activity were re- ported as key responses to Al stress (Tejada-Alvarado et al., 2023; Verma et al., 2023; Yadav et al., 2023). Also, Al exposure disrupts cellular homeostasis, leading to oxida- tive damage and impaired metabolic functions (Yadav et al., 2023). These findings are in line with earlier mecha- nistic studies showing lipid peroxidation, cell aggrega- tion, and antioxidant suppression in Scenedesmus under Al stress(Hamed et al., 2019). 3.3 MORPHOLOGICAL CHANGES Light microscopy analysis revealed that the three tested mi- croalgal species exhibited normal morphology under control conditions, characterized by uniform cell size, intact cell walls, and well-defined chlorophyll pigmentation (Figures 4A, 5A, and 6A). In contrast, exposure to aluminium (Al) induced concentration-dependent morphological alterations, includ- ing abnormal cell enlargement, cytoplasmic disorganization, and localized chlorophyll depletion (Figures 4E–F, 5E–F, and 6E–F). These effects are consistent with the disruption of pho- tosynthetic structures and stress-induced vacuolation com- monly reported under Al toxicity. Cells exposed to silicon (Si) treatment also exhibited minor morphological modifications, but these changes were significantly less pronounced compared to Al-treated groups, suggesting a potential protective effect of Si against structural damage. These findings align with previous reports demonstrating Al-induced structural changes in green microalgae, including cell wall thickening, chloroplast disinte- gration, and pigment degradation (Hamed et al., 2019). Com- parable protective effects of Si supplementation have also been observed, where Si mitigated ultrastructural and pigment-level alterations in algae and higher plants under metal stress (De Sousa et al., 2019; Mock, 2021; Pakrashi et al., 2013; Přibyl et al., 2008; Qi et al., 2024)Taken together, the observed reduc- tions in chlorophyll content, growth, and alterations in cellular morphology highlight the sensitivity of C. vulgaris, H. pluvia- lis, and T. suecica to Al stress, as well as the mitigating role of Si supplementation. Also, the findings of this study carry im- portant practical implications for agricultural water systems, particularly irrigation practices in areas affected by aluminium contamination. By demonstrating that silicon supplementation mitigates Al-induced growth inhibition and chlorophyll deg- radation in C. vulgaris, H. pluvialis, and T. suecica, our results suggest that Si can play a protective role in maintaining the structural and functional integrity of microalgal communities. Figure 4: Light micrographs (40×) of Chlorella vulgaris after 21 days of exposure. (A) Control cells showing normal morphol- ogy with uniform size, intact cell walls, and distinct chlorophyll pigmentation. (B–D) Cells exposed to silicon (Si) at 100, 150, and 200 mg l-1, respectively, exhibiting largely preserved mor- phology with only minor structural modifications and negli- gible pigment loss compared to control. (E–G) Cells exposed to aluminium (Al) at 1, 10, and 100 mg l-1, respectively, displaying concentration-dependent alterations, including cell enlarge- ment, cytoplasmic disorganization, vacuolation, and localized chlorophyll depletion. Representative images are shown from n = 3 independent cultures. Scale bar = 20 µm. Figure 5: Light micrographs (40×) of Haematococcus pluvialis after 21 days of exposure. (A) Control cells showing normal spherical morphology with intact cell walls and well-defined chlorophyll pigmentation. (B–D) Cells exposed to silicon (Si) at 100, 150, and 200 mg l-1, respectively, exhibiting largely pre- served cellular structure with only slight changes in pigmenta- tion and minimal morphological alterations compared to con- trol. (E–G) Cells exposed to aluminium (Al) at 1, 10, and 100 mg l-1, respectively, displaying concentration-dependent abnor- malities, including cell enlargement, deformation of cell shape, partial chlorophyll depletion, and cytoplasmic disorganization. Representative images are shown from n = 3 independent cul- tures. Scale bar = 20 µm. Acta agriculturae Slovenica, 121/4 – 20258 G. ISSAAD et al. Since microalgae are essential contributors to nutrient cycling, oxygen production, and the stability of aquatic ecosystems, safeguarding their viability is crucial for sustaining water qual- ity in agricultural watersheds. These insights can be incorpo- rated into strategies for mitigating the adverse effects of metal contamination by introducing Si amendments into irrigation systems or agricultural runoff management. Controlled Si sup- plementation could reduce the bioavailability and toxicity of Al, thereby enhancing the resilience of aquatic microflora while simultaneously lowering potential risks to crops irrigated with contaminated water. Such approaches could form part of inte- grated water management frameworks that aim to balance ag- ricultural productivity with ecological protection. In a broader context, our results contribute to sustainable water manage- ment practices in agriculture and forestry. Understanding the interactions between Si and Al provides valuable guidance for designing bioremediation strategies that reduce metal stress in aquatic environments, preserve biodiversity, and improve ecosystem services. The incorporation of Si into water manage- ment not only supports the health of microalgal communities but also offers indirect benefits for crop protection, soil qual- ity, and long-term sustainability of agroecosystems. Thus, the outcomes of this research provide both mechanistic insights and practical directions for addressing the challenges posed by metal contamination in managed ecosystems. 4 CONCLUSION Our study demonstrates that aluminium treatment causes significant adverse effects on Chlorella vulgaris, Haematococcus pluvialis, and Tetraselmis suecica, includ- ing growth inhibition, decreased chlorophyll content, and morphological alterations. In contrast, silicon ex- posure exhibits minimal toxicity, suggesting its potential as a protective agent against aluminium stress in aquatic ecosystems. These results highlight the importance of understanding Si–Al interactions in aquatic microorgan- isms, particularly in relation to water quality manage- ment and the stability of aquatic ecosystems connected to agriculture. While the findings are limited to con- trolled laboratory conditions on microalgae and cannot be directly extrapolated to higher plants, they provide useful insight into processes that may influence agricul- tural water systems. Future research should therefore not only explore the molecular mechanisms underlying silicon’s protective effects in microalgae, but also evalu- ate whether such protective interactions occur in crops under field-relevant agricultural conditions. Ethics statement: This research was conducted us- ing microalgae cultures only and did not involve human participants or animal subjects. All procedures were per- formed under controlled laboratory conditions in com- pliance with institutional biosafety guidelines and the ethical standards of the field. Acknowledgements. We would like to thank Dr. Faouzi Dahdouh, and the laboratory team of Cell Toxi- cology of Annaba University of Algeria for their valuable assistance. Conflict of interest:The authors declare no compet- ing interests. Data Availability All data supporting the findings of this study have been deposited in the Zenodo repository and are openly accessible. The dataset includes the original research data in Excel format. The dataset has also been cited in the reference list as: Issaad, G. (2025). Dataset of the physi- ological parameters, dry mass, chlorophyll content and growth inhibition of Chlorella vulgaris, Haematococcus pluvialis, and Tetraselmis suecica exposed to aluminum (Al; 1, 10, and 100 mg l-1) and silicon (Si; 100, 150, and 200 mg l-1) for 7, 14, and 21 days. [Data set]. Zenodo. htt- ps://doi.org/10.5281/zenodo.17665018. Figure 6: Light micrographs (40×) of Tetraselmis suecica after 21 days of exposure. (A) Control cells showing normal mor- phology with characteristic elongated shape, intact cell walls, and uniform chlorophyll pigmentation. (B–D) Cells exposed to silicon (Si) at 100, 150, and 200 mg  l-1, respectively, retained overall structural integrity, with only minor pigment variation and limited morphological alterations compared to control. (E– G) Cells exposed to aluminium (Al) at 1, 10, and 100 mg l-1, re- spectively, exhibited concentration-dependent structural dam- age, including cell enlargement, deformation of the elongated cell shape, chlorophyll depletion, and cytoplasmic disorganiza- tion. Representative images are shown from n = 3 independent cultures. Scale bar = 20 µm. 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