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Article

Compaction of Iron Mining Tailings Impairs Seedling Emergence of Schinus terebinthifolia but Vigor Features Show Tolerance During Early Growth

by
Poliana Noemia da Silva
1,
Vinícius Politi Duarte
2,
Evaristo Mauro de Castro
2,
Bruno Montoani Silva
3,
Josiel de Jesus Santos
3 and
Fabricio José Pereira
2,*
1
Programa de Pós-Graduação em Botânica Aplicada, Departamento de Biologia, Universidade Federal de Lavras, Campus Universitário, Lavras 37200-000, MG, Brazil
2
Instituto de Ciências da Natureza, Universidade Federal de Alfenas, Rua Gabriel Monteiro da Silva, 700, Centro, Alfenas 37130-001, MG, Brazil
3
Programa de Pós-Graduação em Ciência do Solo, Departamento de Ciência do Solo, Universidade Federal de Lavras, Campus Universitário, Lavras 37200-000, MG, Brazil
*
Author to whom correspondence should be addressed.
Forests 2025, 16(6), 950; https://doi.org/10.3390/f16060950
Submission received: 23 April 2025 / Revised: 15 May 2025 / Accepted: 3 June 2025 / Published: 5 June 2025
(This article belongs to the Section Forest Ecophysiology and Biology)
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Abstract

Soil compaction is a well-known harmful process for germination and seedling growth. Studies about compaction in mining tailings have been neglected despite being essential for the reforestation of impacted areas. This work evaluated the effects of compaction of iron mining tailings on the seedling emergence, early growth, and photosynthesis of Schinus terebinthifolia Raddi, a tolerant species with potential for reforestation. Experiments were implemented in a greenhouse where seeds of S. terebinthifolia were sown in iron mining tailings with four compaction treatments: (1) an uncompacted dry tailing, (2) uncompacted moistened tailing, (3) compacted dry tailing, and (4) compacted moistened tailing. Penetration resistance, seedling emergence, emergence speed index, seedling biometry, and photochemical traits were evaluated. Compacted moistened tailings showed the highest penetration resistance and uncompacted dry tailings the lowest. Other treatments showed intermediate means. The compacted moistened tailings produced the lowest seedling emergence rate and emergence speed index, and these parameters showed the highest means at uncompacted dry tailings with other treatments showing intermediate means. The compaction did not affect the seedling’s biometric parameters, with a similar growth among all treatments. S. terebinthifolia seedlings showed improved growth parameters during the experimental period, evidencing the potential of the species for the reforestation of impacted areas by iron mining tailings.

1. Introduction

Brazil is the second largest iron exporter in the world, and its Minas Gerais state is where the largest iron mines are found. Tragic events involving mining activities have been registered for many years [1]. In November 2015 in Mariana City located in Minas Gerais state, Brazil, a massive disaster occurred, being considered the most harmful in the country to this date and one of the largest ever worldwide [1,2]. More than 34 million cubic squares of iron mining tailings were released in this accident, contaminating more than 1200 ha [3].
Iron mining tailings from the Fundão dam showed several potentially toxic elements (PTEs), such as aluminum (Al), cadmium (Cd), chromium (Cr), and lead (Pb), and most of these were below the toxicity levels [3,4,5,6,7]. The toxicity of iron mining tailings is often associated with PTEs. For instance, the presence of cadmium (Cd) caused toxicity for the seed germination and seedling growth of S. terebinthifolia [7]. In addition, an increased availability of iron (Fe), aluminum (Al), cadmium (Cd), and lead (Pb) promoted a higher toxicity in lettuce seed germination [8]. According to Scarpa et al. [6], the presence of PTEs in iron mining tailings impaired the emergence and early seedling growth of Handroanthus spp. trees. Nonetheless, secondary factors can increase the toxicity of the iron mining tailings, such as lowering the pH to five or below [8]. In this context, one secondary factor never investigated for iron mining tailings is the compaction effect of this pollutant. According to Pádua et al. [4] and Matos et al. [9], the particles of iron mining tailings from the Fundão dam failure are small (2 μm or less in diameter); these particles may increase the risk of the compaction of this pollutant being inserted among bigger particles present. Soil compaction is a known process of degradation that impairs seed germination and plant growth [10]; nonetheless, the compaction effects in mining tailings are unclear.
The reforestation of areas impacted by mining tailings is an effective method to accelerate the recovery of these sites. Schinus terebinthifolia Raddi is tolerant to iron mining tailings and capable of germinating and growing in the pollutant despite some degree of toxicity being evident [3,7]. This species shows potential for the reforestation of areas impacted by iron mining tailings [7]. S. terebinthifolia belongs to the Anacardiaceae family and is native to South America but is cultivated worldwide for urban forestation, the reforestation of impacted areas, and as an ornamental tree [11].
This work hypothesizes that compacted iron mining tailings can impair seed germination and seedling growth, but S. terebinthifolia shows some degree of tolerance to this secondary factor. Thus, the objective of this work was to evaluate the effect of the compaction of iron mining tailings on the seedling emergence, growth, and photochemical traits of S. terebinthifolia.

2. Materials and Methods

2.1. Iron Mining Tailings Traits

Iron mining tailing samples were collected 4 km away from Fundão dam in Mariana, state of Minas Gerais, Brazil (20°22′40″ S 43°24′57″ W), and transported to Universidade Federal de Alfenas, Alfenas, state of Minas Gerais, Brazil (21°25′44″ S 45°56′49″ W). Iron mining tailings were stored in plastic bags in a room protected against sources of water, heat, and radiation until the start of experiments. Iron mining tailings were then transported to the Universidade Federal de Lavras, Lavras, state of Minas Gerais, Brazil (21°14′43″ S 44°59′59″ W), for the implementation of experiments.
Iron mining tailing samples were analyzed in the Soil Analysis Laboratory in the Universidade Federal de Lavras, Lavras, state of Minas Gerais, Brazil. The micro- and macronutrient contents as well as potentially toxic elements were analyzed. In addition, the organic matter, pH, and granulometry were also evaluated.
Mining tailings were oven-dried at 60 °C until reaching a constant mass and submitted to different extraction methods for elemental quantification. For this, 500 mg of the tailing was extracted using 50 mL of extractors, including the following: mehlich-1 extractor for phosphorus (P), sodium (Na), potassium (K), iron (Fe), zinc (Zn), manganese (Mn), chromium (Cr), lead (Pb), and copper (Cu) [12]; calcium (Ca), magnesium (Mg), and aluminum (Al) were extracted using KCl 1.0 M [13]; and H+Al was determined according to Raij et al. [14]. The levels of macro- and micronutrients and potentially toxic elements were quantified using an atomic absorption spectrophotometer, AAnalyst 800 (PerkinElmer, Waltham, MA, USA). The pH was measured using the electrode immersed in a solution containing the tailings suspension in potassium chloride (KCl) and calcium chloride (CaCl2) (1:2.5). The granulometry of iron mining tailings was determined according to Bouyoucos [15]. Values for macronutrients, micronutrients, potentially toxic elements, organic matter, pH, and granulometry are shown in Table 1.

2.2. Plant Material and Experimental Design

Seeds of Schinus terebinthifolia Raddi were collected from trees used in urban forestation in Alfenas, state of Minas Gerais, Brazil (21°25′44″ S 45°56′49″ W). Fruits were oven-dried at 40 °C for five days and then stored in glass flasks at 4 °C until the installation of the experiment. Seeds were removed from dried fruits and submitted to a pre-treatment, being immersed in 1.0 mM of gibberellic acid (GA3) for 24 h before sowing. This treatment proved necessary though preliminary tests performed by the group to improve seed germination of S. terebinthifolia, which is naturally very low [6,7].
Seeds were sown in gerbox flasks containing 250 mL of sifted and dried iron mining tailings from the Fundão dam being previously submitted to four compaction treatments: (1) uncompacted dry tailings (DTs), (2) uncompacted moistened tailings (MTs), (3) compacted dry tailings (CDTs), and (4) compacted moistened tailings (CMTs).
Compaction was performed by promoting a pressure of 0.017 Kgf cm−2 (1.67 kPa) by 24 h before sowing. For this, a load weighing 2 kg was placed on the surface of tailings in each gerbox from compacted treatments, staying in this position for 24 h. The pressure was determined by dividing the mass of the load (2 kg) by the surface area of the gerbox (121 cm2). We considered 1 Kgf cm−2 equal to 98.07 kPa, and the kPa values applied were calculated by multiplying 0.017 by 98.07, giving 1.67 kPa. For both MT and CMT treatments, 100 mL of water per gerbox was added, which is about 40% of the volume of tailings used (250 mL), being sufficient to saturate the tailings according to Pádua et al. [4]. For the CMT treatment tailings were moistened before the application of the load.
Seeds were sown after the compaction treatments and penetration resistance analyses were performed. Tailings were re-moistened using 100 mL of water per gerbox and a further 100 seeds per gerbox were added in 0.5 cm depth pits later covered with tailings. Seeds were sown after compaction to avoid damage to their tissues. The experiment was carried out for 60 days in a greenhouse located at Universidade Federal de Lavras, Lavras, state of Minas Gerais, Brazil (21°14′43″ S 44°59′59″ W), with a mean temperature of 26 °C, 12 h photoperiod, 187.8 W m−2, and 60% relative humidity. Water was replaced daily, weighing each gerbox and adding a volume of water equal to the mass lost compared to the previous day, considering that 1 mL of water is equal to 1 g.
For the germination percentage, germination speed index, and penetration resistance the experiment was completely randomized with four treatments (DT, MT, CDT, and CMT) and eight replicates (n = 32). The experimental design was completely randomized in a factorial 2 × 4 scheme with four compaction levels (DT, MT, CDT, and CMT) and ages for the seedlings (15 and 30 days) and eight replicates (n = 64) for the biometric and photosynthetic analyses from seedlings. Each replicate was considered as a gerbox (penetration resistance, germination percentage, and germination speed index) or a seedling (for seedling biometric and photosynthetic analyses).

2.3. Penetration Resistance Analysis

CMT and MT treatments were oven-dried at 40 °C for 5 days before the penetration resistance measurement so that tailings from all tailings were dry at the moment of the test. The penetration resistance was measured using a bench-top penetrometer model MA933 (Marconi, Piracicaba, SP, Brazil). The cylindric register comprises a conic tip with an angle of 30° and diameter of 3.84 mm. Penetration was performed perpendicular to the sample (90°) at 10 cm min−1, and results were given in Kgf.

2.4. Emergence Analysis

The number of seedlings that emerged per gerbox was counted daily and at the end of the experiment, and the emergence percentage (G%) was calculated as follows: E% = (number of emerged seedlings per gerbox/number of seeds sown per gerbox) × 100. The emergence speed index (ESI) was calculated as follows: ESI = Σ (Nn/Dn), where Nn = number of emerged seedlings counted in a given day and Dn = the number of days passed since sowing.

2.5. Seedling Biometry Analysis

Seedlings were collected past 15 and 30 days after emergence and were immediately photographed with a Canon Powershot a630. Images were used for counting the number of leaves and roots and also for the measurements of the leaf area, stem diameter, stem length, and the length of the main and lateral roots. Images were analyzed in the Image J software version 1.45 s [16].
Seedlings were separated into roots, stems, and leaves, and the fresh mass of each organ was measured in an analytical scale model AY220 (Shimadzu, Tokyo, Japan), while for the dry mass, each plant part was oven-dried at 60 °C for 72 h and weighed again. The water content (WC) was calculated as follows: WC = [(FM − DM)/FM] × 100, where FM is the fresh mass and DM is the dry mass, and results are given in percentage. The biomass allocation to each organ (O%) was calculated as follows: O% = (DMO/TDM) × 100 where DMO is the dry mass of the organ and TDM is the total dry mass. Total fresh and dry masses were obtained by the sum of the respective mass of each organ.

2.6. Photochemical Analysis of Photosynthesis

Photochemical analyses were performed on the first two fully expanded leaves (cotyledons in the case of S. terebinthifolia) per seedling, at the middle region of the leaf on the adaxial side during the morning (between 8 and 11 a.m.). The leaves selected were in good phytosanitary condition without evident damage, chlorosis, or infections.
Photochemical parameters were evaluated using a portable fluorometer MINI-PAM (Walz, Wetzlar, Germany). The effective photochemical yield of the photosystem II (ϕPSII) and the electron transport rate were evaluated. We could not evaluate the maximum effective yield of the photosystem II (Fv/Fm) because the leaves were too fragile and did not support the clip for dark measurements. The total chlorophyll content was estimated using a portable chlorophyll meter SPAD-502 (Konica Minolta, Tokyo, Japan).

2.7. Statistical Analyses

Data was submitted to the Shapiro–Wilk test for normality and then to one-way ANOVA (for penetration resistance, germination percentage, and germination speed in-dex) or two-way ANOVA (for seedling traits). Further data was submitted to the Tukey test for 5% of error probability. Statistical analyses were performed using the SISVAR 5.6 software [17].

3. Results

Results from the one-way ANOVA and the two-way ANOVA are shown in Table 2.
The compaction of iron mining tailings promoted significant effects on the penetration resistance (Table 2). Moistened treatments showed higher means for penetration resistance, the CMT showed the highest values followed by the MT, and the dry treatments (MT and CDT) showed the lowest means with no resistance (Figure 1).
Compaction caused significant effects on the seedling emergence and emergence speed index (Table 2). Compaction reduced the seedling emergence percentage, and the CMT and MT treatments had the lowest means, the DT showed the highest emergence, and the CDT showed intermediate means (Figure 2A). Similar results were found for the emergence speed index, and the lowest mean was promoted by the CMT and the highest by the CDT; DT and MT treatments showed intermediate means (Figure 2B).
No significant interaction was found between the seedling’s age and compaction treatments for the leaf area and number of leaves per seedling (Table 2). The compaction promoted no significant effect on the leaf area (Figure 3A) or the number of leaves (Figure 3C) from S. terebinthifolia seedlings growing in iron mining tailings. S. terebinthifolia seedlings showed an increased leaf area (Figure 3B) and number of leaves (Figure 3D) from 15 to 30 days independently of compaction treatments.
There was no significant interaction between the tailing compaction and seedling age for the stem length, stem diameter, and seedling quality index (Table 2). The compaction promoted no significant modification in the stem length (Figure 4A) and diameter (Figure 4C). Seedlings of S. terebinthifolia increased their stem length (Figure 4B) and diameter (Figure 4D) from 15 to 30 days.
There was no significant interaction between the compaction and seedling age for the main root length, the lateral root length, and the number of roots per seedling (Table 2). Compaction promoted no significant effect on the main root length of S. terebinthifolia seedlings (Figure 5A), and no significant differences were found between 15 and 30 days of a seedling’s age (Figure 5B). Compaction increased the lateral root length, with the highest means found in the CMT treatment and the lowest in the DT seedlings; MTs and CDTs showed intermediate means (Figure 5C). The lateral root length increased from 15 to 30 days in S. terebinthifolia leaves, independently of the compaction (Figure 5D). Compaction promoted no significant modification in the number of roots per seedling (Figure 5E), but this parameter increased from 15 to 30 days in S. terebinthifolia seedlings (Figure 5F).
No significant interaction between the compaction and seedling age was found for the total fresh mass and total dry mass (Table 2); however, a significant interaction was found for the water content (Table 2). Compaction promoted no significant effect on the total fresh mass (Figure 6A) and total dry mass (Figure 6C) of S. terebinthifolia seedlings. Both the total fresh (Figure 6B) and dry masses (Figure 6D) increased from 15 to 30 days in S. terebinthifolia grown in iron mining tailings, independently of the compaction. The compaction and pre-moistening of iron mining tailings promoted a higher water content in 15-day-old seedlings of S. terebinthifolia since CMTs, MTs, and CDTs showed higher means compared to DTs at this age; however, no significant differences in this parameter were found for 30-day-old seedlings (Figure 6E). In addition, compacted treatments (CMT and CDT) showed no significant differences for the seedling water content when comparing 15 to 30 days of the seedling’s growth; nonetheless, uncompacted treatments (MT and DT) showed an increase in this parameter from 15 to 30 days (Figure 6E).
There was no significant interaction between the compaction and seedling age for the leaf, stem, and root dry masses (Table 2). Compaction promoted no significant effect for the leaf (Figure 7A), stem (Figure 7C), and root (Figure 7E) dry masses of S. terebinthifolia growing in iron mining tailings. Seedlings from S. terebinthifolia increased their leaf (Figure 7B), stem (Figure 7D), and root (Figure 7F) dry masses from 15 to 30 days, independently from the tailing compaction.
There was no significant interaction between the compaction and seedling age for the leaf, stem, and root biomass allocation (Table 2). Compaction promoted no significant effect for the leaf (Figure 8A), stem (Figure 8C), and root (Figure 8E) biomass allocation from S. terebinthifolia growing in iron mining tailings. S. terebinthifolia seedlings increased their leaf biomass allocation (Figure 8B) from 15 to 30 days independently from the tailing compaction, while the allocation to roots decreased (Figure 8F), and no significant modification was observed in the stem allocation (Figure 8D) in the same period.
No significant interaction between the compaction and seedling age was found for the chlorophyll content, electron transfer rate, and effective photochemical yield (Table 2). Compaction promoted no significant differences in the estimated total chlorophyll content (Figure 9A), electron transfer rate (Figure 9C), and effective photochemical yield (Figure 9E) of S. terebinthifolia seedlings growing in iron mining tailings. The chlorophyll content was not significantly modified between 15 and 30 days of S. terebinthifolia seedlings’ growth in iron mining tailings (Figure 9B). The electron transfer rate of S. terebinthifolia photosynthetic cotyledons increased from 15 to 30 days of the seedling’s growth in iron mining tailings (Figure 9D), but the effective photochemical yield decreased in this period (Figure 9F).

4. Discussion

4.1. Compaction of Iron Mining Tailings and Its Effect on S. terebinthifolia Seedling Emergence

The compaction methods applied in this experiment were effective, increasing the penetration resistance of pre-moistened (MTs) and compacted moistened tailings (CMTs). The penetration resistance varies with the soil texture and hydration, which can change due to natural or anthropic influences [10,18]. Results showed that pre-moistened tailings which were dried previously to the penetration resistance analysis were a determinant factor for the compaction of the pollutant because both compacted (CMTs) and uncompacted (MTs) moistened tailings increased their penetration resistance. The increase in the penetration resistance is related to the higher density and lower porosity in soils [10]. Drying the soil removes water located on the surface of its particles or stored in pores, causing tailings’ compaction by approaching its particles and reducing porosity. Previous studies show that the penetration resistance increased with the soil water loss [18,19]. In addition, compaction decreases soil porosity, increasing its density [20]. The moisture and humidity increased iron mining tailings’ compaction, but the surface pressure promoted by the load further increased the penetration resistance, as shown in the CMT treatment which showed the highest means for the penetration resistance. Plant survival and establishment are more difficult in compacted soils [20], and this can add a secondary factor impeding reforestation programs in areas impacted by iron mining tailings. It is important to note that only the compaction of dry tailings caused no significant effect on the penetration resistance (the CDT treatment), indicating that the tailing’s water content is important for the compaction of this pollutant. Thus, both the surface pressure and cycles of moisture and evaporation may cause the compaction of iron mining tailings, adding a secondary factor for plants to overcome.
The iron mining tailings showed a heterogeneous texture, and 51% of its particles comprised silt and clay, which are smaller than sand. This is corroborated by other works with iron mining tailings from the Fundão dam, which showed small particles mainly comprising clay of a very small size (1.2 μm) [4,21]; however, these works used a different method, with the direct measuring of the diameter of the particles in the microscope. Clay soils show a higher water retention capacity compared with sandy soils [10,22,23]. According to Pádua et al. [4], the irrigation of the field capacity of iron mining tailings caused water-logging because of the lower porosity reducing the growth and development of Copaifera langsdorffii Desf., suggesting that particles in iron mining tailings are small and promoting a lower porosity in this pollutant. Thus, the compaction promoted in moistened iron mining tailings (the CMT treatment) or by the water evaporation in moistened tailings (MTs) may have reduced its porosity, approaching its particles which can harm plant establishment.
Similarly to previous works, the iron mining tailing comprises mostly silt and sand [23,24]. According to Zanchi et al. [25] this composition can reduce the porosity of the substrate. It is also important to note that small particles can be inserted among bigger ones, reducing the soil porosity [26], which can harm the growth and development of plants by limiting water and aeration [25]. In addition, the iron mining tailing shows limited organic matter contents (Table 1), and this can reduce the formation and stabilization of particle aggregates which are important components of the soil’s structure [27]. Aggregates help reduce the compaction process, improving the porosity, aeration, and water content in the soil [28,29].
The significant reduction in germination traits from S. terebinthifolia seeds in compacted and moistened tailings (CMT and MT treatments) supports the hypothesis that compaction is harmful to seed germination and is a relevant secondary factor affecting iron mining tailings. This can be associated with the lower porosity found in compacted soils that decreases the water and oxygen availability [18]. Germination is one of the most sensitive stages of plant development, and it is highly dependent on water and oxygen availability [30,31]. Thus, the compaction of iron mining tailings may have caused limitations to water and oxygen availabilities for S. terebinthifolia seeds. Soil compaction reduces the seed germination of other plant species [32,33,34]. Methods like soil scarification can be used to improve the permeability of compacted soils [35,36], which can enhance the water and air availability in the substrate, representing potential for the management of areas impacted by compacted iron mining tailings.

4.2. Tolerance of S. terebinthifolia Seedlings to Compaction of Iron Mining Tailings

Although compaction impaired the seed germination, S. terebinthifolia seedlings showed a tolerance to compacted tailings because no significant modification was found for the majority of growth parameters evaluated (leaf area, number of leaves, stem length and diameter, main root length, number of roots, fresh and dry masses, and their allocation). The absence of a significant growth modification is an important trait for compaction-tolerant species, such as Tabebuia aurea (Silva Manso) Benth. & Hook.f. ex S. Moore [37] and Moringa oleifera Lam. [35], which showed no significant growth changes in compacted soils. There are no comparable works on iron mining tailing compaction effects on seedling growth; this the first report of such effects, but the absence of a growth restriction from S. terebinthifolia in compacted treatments supports its tolerance and potential for the revegetation of impacted areas.
The increase in the lateral root length in compacted iron mining tailings can be an interesting tolerance trait of S. terebinthifolia (Figure 5C). Roots are responsible for water and nutrient uptake. The longer roots produced in compacted iron mining tailings by S. terebinthifolia seedlings may be more efficient in compensating for compaction’s negative effects. Similar results were found for Hordeum vulgare L. grown in growth chambers with an external pressure system [38]. An increased lateral root growth was also reported for conifer trees growing in compacted soils, improving their root system [39]. In addition, the development of the root system is an important vigor trait in compacted soils because it promotes better shoot growth [40]. The increased proportion of lateral roots may be stimulated by the shoot, compensating for its development under stress conditions [41]. The improved growth of S. terebinthifolia roots in compacted iron mining tailings supports its tolerance for this pollutant and potential for the revegetation of impacted areas.
The absence of negative effects in photochemical traits of S. terebinthifolia seedlings, like the chlorophyll content (Figure 9A), electron transfer rate (Figure 9C), and effective photochemical yield (Figure 9E), indicate that this species is tolerant to compacted tailings, maintaining its photosynthesis. This is an important result since non-tolerant species show decreased photosynthesis under compacted soils [42,43]. Reduced photosynthesis may harm plant growth [44], but its stability is important for efficient plant growth. Soil compaction reduces photochemical traits in beans [45] and wheat [46], causing problems for their growth and development. Thus, stable photosynthesis is an important tolerant trait in S. terebinthifolia, supporting the capacity of this species for the reforestation of areas impacted by compacted iron mining tailings.

4.3. Early Growth and Development of S. terebinthifolia Seedlings in Compacted Iron Mining Tailings

Most growth parameters and photochemical traits of S. terebinthifolia seedlings showed an increase from 15 to 30 days after germination independently of the compaction treatment, supporting its tolerance to this pollutant and its potential for use in reforestation systems. This species was already reported as tolerant to iron mining tailings, showing a capacity to germinate in early growth [6]. This species can suffer some degree of toxicity to its germination and early growth despite being capable of surviving and growing in iron mining tailings [7]. The variation in the tolerance capacity may be caused by the seed set used [7] or the great variability in the iron mining tailings’ composition [4,5,6,7,8,21]. It is also important to note that factors such as the pH of iron mining tailings affect its toxicity, being more toxic at pH values of five or lower due to increased Al and Fe availabilities [8]. Although the species showed variations in its iron mining tailing tolerance, in this work results from growth, development, and photochemical traits support its tolerance to the pollutant, most of which increased during early growth. Because this investigation lasted 60 days and seedlings were just 30 days old, works with longer experimental times may be important to understand the responses of the species in reforestation systems and also to evaluate gas exchange parameters, since the leaves of the species are fragile at the early stage, which does not allow for the use of most gas exchange devices.

5. Conclusions

Surface pressure and moisture followed by drying promote the compaction of iron mining tailings. Compacted mining tailings reduce seed germination traits in S. terebinthifolia; however, seedlings of this species show no effects of compaction on its early growth, improving most growth parameters from 15 to 30 days of the experiment. The compaction of mining tailings promotes no significant effects on the photochemical stage of the photosynthesis of S. terebinthifolia seedlings. The capacity to grow in compacted mining tailings and the absence of significant negative effects support the tolerance of S. terebinthifolia for compacted iron mining tailings.

Author Contributions

Conceptualization, P.N.d.S. and F.J.P.; methodology, P.N.d.S., V.P.D., E.M.d.C., B.M.S., J.d.J.S., and F.J.P.; formal analysis, P.N.d.S. and F.J.P.; investigation, P.N.d.S. and F.J.P.; resources, F.J.P.; data curation, P.N.d.S. and F.J.P.; writing—original draft preparation, P.N.d.S. and F.J.P.; writing—review and editing, P.N.d.S. and F.J.P.; supervision, F.J.P.; project administration, F.J.P.; funding acquisition, F.J.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by FAPEMIG [Fundação de Amparo à Pesquisa do estado de Minas Gerais (Minas Gerais State Research Foundation)], grant number APQ-02960-21.

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Acknowledgments

This work was supported by CNPq [Conselho Nacional de Desenvolvimento Científico e Tecnológico (National Counsel of Technological and Scientific Development)], CAPES [Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Coordination for the Improvement of Higher Education Personnel)]—Finance Code 001 to complete the present study, and FAPEMIG [Fundação de Amparo à Pesquisa do estado de Minas Gerais (Minas Gerais State Research Foundation)].

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 16 00950 g001
Figure 1. Penetration resistance from four different compaction treatments in iron mining tailings. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 32). Bars = standard error.
Figure 1. Penetration resistance from four different compaction treatments in iron mining tailings. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 32). Bars = standard error.
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Forests 16 00950 g002
Figure 2. Seedling emergence (A) and emergence speed index (B) from Schinus terebinthifolia seeds sown in iron mining tailings with different compaction levels. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 32). Bars = standard error.
Figure 2. Seedling emergence (A) and emergence speed index (B) from Schinus terebinthifolia seeds sown in iron mining tailings with different compaction levels. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 32). Bars = standard error.
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Forests 16 00950 g003
Figure 3. Leaf area (A,B) and number of leaves per seedling (C,D) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Figure 3. Leaf area (A,B) and number of leaves per seedling (C,D) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
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Forests 16 00950 g004
Figure 4. Stem length (A,B) and stem diameter (C,D) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Figure 4. Stem length (A,B) and stem diameter (C,D) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
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Forests 16 00950 g005
Figure 5. Main root length (A,B), lateral root length (C,D), and number of roots per seedling (E,F) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Figure 5. Main root length (A,B), lateral root length (C,D), and number of roots per seedling (E,F) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
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Forests 16 00950 g006
Figure 6. Total fresh mass (A,B), total dry mass (C,D), and water content (E) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Figure 6. Total fresh mass (A,B), total dry mass (C,D), and water content (E) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
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Forests 16 00950 g007
Figure 7. Leaf (A,B), stem (C,D), and root (E,F) dry masses from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Figure 7. Leaf (A,B), stem (C,D), and root (E,F) dry masses from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
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Forests 16 00950 g008
Figure 8. Biomass allocation to leaves (A,B), stem (C,D), and roots (E,F) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Figure 8. Biomass allocation to leaves (A,B), stem (C,D), and roots (E,F) from Schinus terebinthifolia seedlings growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
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Forests 16 00950 g009
Figure 9. Chlorophyll content (A,B), electron transfer rate (C,D), and effective photochemical yield (E,F) from Schinus terebinthifolia photosynthetic cotyledons growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Figure 9. Chlorophyll content (A,B), electron transfer rate (C,D), and effective photochemical yield (E,F) from Schinus terebinthifolia photosynthetic cotyledons growing in iron mining tailings with different compaction levels and seedling age. DTs = uncompacted dry tailings, MTs = uncompacted moistened tailings, CDTs = compacted dry tailings, and CMTs = compacted moistened tailings. Means followed by the same letter do not differ significantly according to Tukey’s test to p < 0.05 (n = 64). Bars = standard error.
Forests 16 00950 g009
Table 1. Granulometry and concentrations of macro- and micronutrients as well as potentially toxic elements (PTEs) in iron (Fe) mining tailings resulting from the failure of the Fundão dam in Mariana, MG. * Maximum value permitted [7].
Table 1. Granulometry and concentrations of macro- and micronutrients as well as potentially toxic elements (PTEs) in iron (Fe) mining tailings resulting from the failure of the Fundão dam in Mariana, MG. * Maximum value permitted [7].
Macronutrientsmg kg−1Maximum Concentration Values Permitted for Potentially Toxic Elements (PTE) (mg kg−1) *
Phosphorus (P)10.7-
Magnesium (Mg)18.2-
Potassium (K)41.6-
Calcium (Ca)226.4-
Micronutrientsmg kg−1
Manganese (Mn)200.4-
Iron (Fe)189.3-
Zinc (Zn)0.7300.0
Copper (Cu)1.163.0
Sodium (Na)37.0-
Potentially toxic elements(mg kg−1)
Aluminum (Al)80.9-
Chromium (Cr)0.0775.0
Lead (Pb)0.0272.0
Other characteristics
pH5.7-
Organic matter (mg kg−1)4.3-
Granulometry(%)
Clay12-
Silt39-
Sand49-
Table 2. Summarized ANOVA results for all variables analyzed, including mean square values, F test results, and p values. CV% = coefficient of variation.
Table 2. Summarized ANOVA results for all variables analyzed, including mean square values, F test results, and p values. CV% = coefficient of variation.
VariableCV%Mean Square ValueF Test Valuep Value
Penetration resistance (C)50.435.89404653.517<0.0001
Germination percentage (C)44.3773.0833335.8520.0038
Germination speed index (C)43.330.1862494.5750.0118
Number of leaves (C)15.740.4543271.1010.3539
Number of leaves (A)15.7424.74054059.949<0.0001
Number of leaves (C × A)15.740.7122711.7260.1685
Leaf area (C)31.010.1160120.4220.7374
Leaf area (A)31.0125.73159093.707<0.0001
Leaf area (C × A)31.010.1510090.5500.6498
Stem length (C)20.530.4657041.6580.1830
Stem length (A)20.532.6039879.2690.0032
Stem length (A × C)20.530.2996901.0670.3681
Stem diameter (C)23.480.0003811.0290.3845
Stem diameter (A)23.480.01787848.292<0.0001
Stem diameter (C × A)23.480.0002500.6740.5705
Number of roots (C)49.6719.7156150.7530.5239
Number of roots (A)49.67662.20971025.290<0.0001
Number of roots (C × A)49.677.4679800.2850.8361
Main root length (C)46.811.8884681.9210.1341
Main root length (A)46.810.2805850.2850.5949
Main root length (C × A)46.810.4542570.4620.7096
Lateral root length (C)47.122.0299132.7470.0494
Lateral root length (A)47.1222.31102230.188<0.0001
Lateral root length (C × A)47.120.7666891.0370.3816
Total fresh mass (C)33.95135.8324580.5280.6646
Total fresh mass (A)33.9516,287.77812563.278<0.0001
Total fresh mass (C × A)33.95190.2911250.7390.5320
Total dry mass (C)30.956.4274580.3320.8024
Total dry mass (A)30.95831.40512542.901<0.0001
Total dry mass (C × A)30.9511.7674580.6070.6124
Water content (C)11.94465.5735487.2320.0002
Water content (A)11.941514.53088823.526<0.0001
Water content (C × A) *11.94293.6434104.5610.0055 *
Leaf dry mass (C)28.852.8203330.6470.5872
Leaf dry mass (A)28.85329.67200075.648<0.0001
Leaf dry mass (C × A)28.855.2243331.1990.3164
Stem dry mass (C)34.360.4670000.6430.5897
Stem dry mass (A)34.3624.864500034.250<0.0001
Stem dry mass (C × A)34.360.6975000.9610.4160
Root dry mass (C)55.943.9737920.6250.6013
Root dry mass (A)55.9432.3851255.0910.0271
Root dry mass (C × A)55.943.1081250.4890.6912
Leaf dry mass allocation (C)18.52130.3533711.4480.2361
Leaf dry mass allocation (A)18.52581.8507816.4620.0132
Leaf dry mass allocation (C × A)18.5277.0942880.8560.4679
Stem dry mass allocation (C)25.435.5003270.2690.8480
Stem dry mass allocation (A)25.435.3251200.2600.6116
Stem dry mass allocation (C × A)25.4312.7487070.6230.6026
Root dry mass allocation (C)55.943.9737920.6250.6013
Root dry mass allocation (A)55.9432.3851255.0910.0271
Root dry mass allocation (C × A)55.943.1081250.4890.6912
Chlorophyll content (C)21.68114.8116731.3960.2457
Chlorophyll content (A)21.68302.2793913.6760.0569
Chlorophyll content (C × A)21.68151.2953371.8400.1418
Effective photochemical yield (C)12.210.0052050.9230.4316
Effective photochemical yield (A)12.210.745344132.175<0.0001
Effective photochemical yield (C × A)12.210.0037780.6700.5718
Electron transfer rate (C)42.8356.5785121.2400.2969
Electron transfer rate (A)42.834179.75579291.616<0.0001
Electron transfer rate (C × A)42.8363.8017781.3980.2452
The p value limit of the software was 0.0001, so results lower than this limit are given as p < 0.0001. (C) = compaction (compacted iron mining tailing when moistened to field capacity (CMT), compacted dried iron mining tailing (CDT), not compacted iron mining tailing when moistened to field capacity (MT), and not compacted dried iron mining tailing (DT)); (A) = age (15 days or 30 days). All variables showed no significant interaction at p < 0.05, except for those indicated by *.
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da Silva, P.N.; Duarte, V.P.; de Castro, E.M.; Silva, B.M.; Santos, J.d.J.; Pereira, F.J. Compaction of Iron Mining Tailings Impairs Seedling Emergence of Schinus terebinthifolia but Vigor Features Show Tolerance During Early Growth. Forests 2025, 16, 950. https://doi.org/10.3390/f16060950

AMA Style

da Silva PN, Duarte VP, de Castro EM, Silva BM, Santos JdJ, Pereira FJ. Compaction of Iron Mining Tailings Impairs Seedling Emergence of Schinus terebinthifolia but Vigor Features Show Tolerance During Early Growth. Forests. 2025; 16(6):950. https://doi.org/10.3390/f16060950

Chicago/Turabian Style

da Silva, Poliana Noemia, Vinícius Politi Duarte, Evaristo Mauro de Castro, Bruno Montoani Silva, Josiel de Jesus Santos, and Fabricio José Pereira. 2025. "Compaction of Iron Mining Tailings Impairs Seedling Emergence of Schinus terebinthifolia but Vigor Features Show Tolerance During Early Growth" Forests 16, no. 6: 950. https://doi.org/10.3390/f16060950

APA Style

da Silva, P. N., Duarte, V. P., de Castro, E. M., Silva, B. M., Santos, J. d. J., & Pereira, F. J. (2025). Compaction of Iron Mining Tailings Impairs Seedling Emergence of Schinus terebinthifolia but Vigor Features Show Tolerance During Early Growth. Forests, 16(6), 950. https://doi.org/10.3390/f16060950

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