Does Seed Coating Alter the Physiological Potential of Small-Seeded Native Species Used in Ecological Restoration?

Abstract

Seed coating technologies can enhance germination and seedling vigor, thereby improving the success of direct seeding in ecological restoration. These techniques involve applying protective and bioactive materials to the seed surface to improve performance under field conditions. This study aimed to evaluate the efficacy of different seed coating materials on germination and early seedling development of two native tree species, commonly used in ecological restoration: Guazuma ulmifolia Lam. and Mimosa bimucronata (DC.) Kuntze. Eight treatments were tested, comprising three coating techniques and an uncoated control. For pelleting, coating mass, agricultural limestone, potassium silicate, and gypsum were used. Film coating included drying powder with graphite and without finishing agent, and encapsulation involved sodium alginate and copper sulfate. The experiment followed a completely randomized design with ten replicates of 30 seeds, totaling 2,400 seeds per species. Pelleting and film coating did not significantly affect germination or early development, although responses varied depending on the species and materials used. In M. bimucronata, pelleting with limestone promoted the greatest root length. In G. ulmifolia, pelleting with gypsum delayed germination, while potassium silicate pellets yielded the most uniform germination speed. Encapsulation reduced germination percentages in both species. Overall, pelleting and film coating show potential as viable techniques for enhancing seed performance in ecological restoration efforts.

Keywords:
Germination; Direct seeding; Pelleting; Encapsulation; Seedlings; Seed Technology.

HIGHLIGHTS

• Pelleting and film coating do not impair germination of native tree species.

• Encapsulation with alginate and copper sulfate significantly reduces germination.

• Pelleting with agricultural limestone enhances root growth.

• Agricultural gypsum and potassium silicate promote more uniform germination speed.

INTRODUCTION

The global effort to restore degraded ecosystems has gained momentum in recent years, driven by urgent environmental and socio-economic concerns. In recognition of this need, the United Nations (UN) declared 2021-2030 the Decade on Ecosystem Restoration, prompting countries to adopt international commitments and implement large-scale ecological restoration initiatives [¹-⁴]. Among the available techniques, direct seeding has emerged as a cost-effective and scalable method for restoring native vegetation [⁵-⁷]. However, it faces challenges such as low establishment and survival rates of species in the field [⁸], particularly for species with smaller seeds [⁹,¹⁰], which are more vulnerable to desiccation, limited seedling reserves, and often exhibit lower germination rates and require more precise sowing depth, making field sowing more technically demanding and management-intensive. Additional issues include low emergence [¹¹], seed availability [¹²,¹³], and seed quality [¹⁴]. Recent research has identified seed wastage and poor early emergence as critical bottlenecks to the success of direct seeding [¹⁵], underscoring the need for strategies that improve seedling establishment and reduce seed loss in restoration contexts.

To overcome these challenges, seed enhancement technologies, such as coating, have been increasingly adopted to improve seed performance under field conditions [¹⁶-¹⁹]. Seed coating involves applying external materials to the seed surface [²⁰], altering its physical properties to improve sowing efficiency by standardizing seed shape, mass, and size [²⁰,²¹]. Common coating techniques include: (i) pelleting, which incorporates materials that increase seed size and roundness [¹⁶,²²]; (ii) encapsulation, which uses hydrogels and cross-linking agents like aluminum chloride to form a gel capsule around the seed [²³,²⁴]; and (iii) film coating, which applies a thin layer of active ingredients such as agrochemicals or inert powders [¹⁷,²⁰].

These techniques can facilitate mechanized sowing, improve seed handling, and synchronize germination and emergence [²⁰]. Additionally, seed coating can improve soil-seed contact, regulate water uptake, and protect seeds from physical and environmental stressors, which are critical factors for enhancing seedling emergence in direct seeding systems, especially for small-seeded species [¹⁸]. The effectiveness of seed coating depends largely on the choice of coating materials, which can significantly influence seed vigor and germination performance [²⁵]. Materials such as mineral powders, bio-stimulants, and pesticides have been explored for their potential to enhance seedling establishment [¹⁷,²⁰,²³]. However, further research is needed to assess the specific effects of these materials on native tree species commonly used in ecological restoration, in order to inform best practices and optimize treatment protocols.

In this study, we hypothesize that seed germination and vigor are key determinants of successful direct seeding [¹⁵,²⁶], and that the efficiency of seed coating for forest species varies depending on the method and material used. Therefore, our objective is to evaluate the effectiveness of different seed coating materials on native tree species, guided by the following question: How can seed coating improve the germination and early development of native tree species used in direct seeding for ecological restoration?

MATERIAL AND METHODS

Criteria, species selection and quality tests

To assess the potential of direct seeding for ecological restoration, we considered two key factors that influence initial plant establishment: the selection of suitable species [¹⁵] and their seedling emergence capacity in field conditions [²⁷]. Based on these principles, we used two species with smaller seeds (> 10,000 seeds per kilogram), identified as having low success in direct seeding [¹⁰,²⁸]. The selection criteria included (a) species commonly used in direct seeding, (b) species with high laboratory germination rates, and (c) species with small seeds. Based on this, we selected the native forest tree species Guazuma ulmifolia Lam. and Mimosa bimucronata (DC.) Kuntze, native forest tree species.

Both species are pioneer trees recommended for ecological restoration [²⁹], and exhibit germination rates above 50% under laboratory conditions once dormancy is overcome [³⁰,³¹]. They are also used to restore degraded areas via direct seeding [¹⁰,¹⁵,³²].The seed lots were assembled from nine mother trees of Guazuma ulmifolia Lam. and seven mother trees of Mimosa bimucronata (DC.) Kuntze, all located in the municipality of Promissão, São Paulo State, Brazil (21°21′12″S, 49°49′06″W), within areas of semi-deciduous seasonal forest remnants near the Tietê River reservoir. The seeds of both species were collected between September and October. The seeds were donated by AES Brasil, an energy company that maintains environmental restoration programs in the region, and were used exclusively for scientific research. As the material was obtained through institutional donation, individual herbarium vouchers of the mother trees are not available. The available information on geographic origin and habitat is provided here to ensure transparency and reproducibility regarding the biological source of the seeds. To assess physical quality, purity test, thousand-seed weight, and moisture content were conducted (Table 1) according to the Rules for Seed Analysis [³³] and the International Seed Testing Association [³⁴].

Table 1
Analyses of the initial physical and physiological quality of Guazuma ulmifolia and Mimosa bimucronata seed lots. P%= purity percentage; TSW= Thousand-seed weight (grams); Ns= number of seeds/kg; Mc= Moisture content (%);

Species	P%	TSW	Ns	Mc%
Guazuma ulmifolia	99.6	6,5976	151,570	10.3
Mimosa bimucronata	99.8	8,6001	116,278	10.1

Coating process

Seed coating was tested using eight treatments with pelleting, encapsulation, and film coating methods (Table 2). A completely randomized experimental design was employed, with ten replicates per treatment. Each replicate used 30 coated seeds, totaling 300 seeds per treatment and 2,400 seeds per species throughout the experiment.

Table 2
Description of treatments and materials tested on seeds in each coating method.

Technique	Code	Treatment
Control	T1	Uncoated
Pelleting	T2	Laborsan® coating mass
	T3	Agricultural limestone
	T4	Potassium silicate
	T5	Agricultural gypsum (Calcium sulphate dihydrate)
Encapsulation	T6	Sodium alginate (Alg) and copper II sulfate (CuSO4)
Film-coating	T7	Drying powder without finishing agent
	T8	Drying powder with graphite

Dormancy and asepsis of the two species were addressed according to the Instructions for Forest Seed Analysis [³⁵]. These procedures were followed for all treatments. To overcome dormancy in M. bimucronata, seeds were soaked in distilled water at 80°C. After removing the heat source, the seeds remained submerged for 24 hours. G. ulmifolia seeds were immersed in water at 90°C and left for one hour after removing the heat source. Seed asepsis involved soaking in a detergent solution (5 drops of detergent per 100 mL of water), followed by rinsing in running water, immersion in a sodium hypochlorite solution (5% solution of the commercial product, which contains 2.5% active ingredient) for 2 to 5 minutes, and three final rinses in water.

The coating materials were chosen based on their significant attributes for initial plant growth [³⁶,³⁷], as well as their market availability. These included agricultural limestone (CaO-42%; MgO-8%), which acts as a source of calcium and magnesium important for cell wall strength and enzyme activation; potassium silicate (K-10%; Si-25%), a product rich in soluble silicon and potassium, known to enhance plant productivity, improve resistance to biotic and abiotic stresses, and regulate water loss; agricultural gypsum (Ca-18%; S-15%), which provides calcium and sulfur essential for root development and nutrient uptake; and a commercial seed coating mass from Laborsan®. All materials were in powder form. In the pelleting method (T2, T3, T4, and T5), materials were added in a 3:1 ratio, with six grams of each powdered material (coating mass from Laborsan®, agricultural limestone, potassium silicate, and agricultural gypsum) for every two grams of G. ulmifolia seeds, and 7.7 grams of powdered materials for every 2.6 grams of M. bimucronata seeds.

The pelleting process was carried out using a specialized apparatus comprising a rotating container measuring 15 x 20 cm, fitted with a mini-motor equipped with a reduction gearbox and speed control (Figure 1). This container was affixed to a polyvinyl chloride (PVC) pipe structure at a 45º angle. Varnished wooden flaps (0.5 cm x 15 cm) were affixed to the container to facilitate seed movement. Seeds were added to the container, maintaining a rotation speed of 60 rpm. Gradually, seeds were sprayed with an agglutinating material comprising white glue based on PVA (polyvinyl acetate) at a concentration of 20%.

Figure 1
Scheme A: Equipment for pelleting (above) and seeds of Mimosa bimucronata and Guazuma ulmifolia before and after pelleting. Scheme B: Encapsulation process: Mimosa bimucronata and Guazuma ulmifolia seeds (a) were submerged in a container filled with sodium alginate solution and extracted using a pipette (b). These seeds, now coated with alginate, were subsequently immersed in copper sulfate solution using the dripping method (c), resulting in the formation of alginate + copper sulfate capsules (d). After the capsules were formed, they were taken out of the container and laid on filter paper (e) to eliminate excess solution. A comparison between seeds with and without encapsulation (f). Scheme C: The post-drying agent application (film coating technique) for the two species tested. Arrows on the left indicate the agitation movement.

A plastic container with a nozzle opening of 0.5 mm was employed for spraying. The pelleting materials were divided into ten equal parts (six grams and 7.7 grams divided by 10) and added progressively using a sieve with a 1 mm opening. This division of materials allowed for improved aggregation of seed materials during the pelleting process. With each portion of pelleting material added to the seeds, adhesive totaling 3.2 ml was applied by the end of the process. Subsequently, pelleted seeds were dried for 24 hours at room temperature (25-26ºC) upon completion of the process.

To evaluate the effectiveness of encapsulation (T6), we prepared a sodium alginate solution (2% w/v) in distilled water (Figure 1), a commonly used material for seed coating [³⁸]. Seeds were submerged in the alginate solution for one minute and subsequently extracted using a Pasteur pipette. Encapsulation was performed using the dripping method [³⁹], in which the alginate-coated seeds were immersed in a copper (II) sulfate (CuSO₄) solution (1.5% w/v) for 60 minutes to promote ionic cross-linking and capsule formation.

The use of CuSO₄ as a cross-linking agent, instead of the conventional CaCl₂, was based on its dual functionality: copper ions (Cu²⁺) are capable of promoting alginate gelation through coordination with carboxyl groups, forming stable cross-linked structures comparable to those obtained with calcium ions (Ca²⁺), while also conferring antifungal and antimicrobial properties to the encapsulated seeds [⁴⁰]. The selected concentration (1.5%) and exposure time (60 min) were determined from previous studies that optimized capsule integrity and polymer stability under similar conditions [⁴¹,⁴²].

For the film coating process (T7 and T8), two drying powders were utilized, one without a finishing agent (T7) and the other containing graphite (T8) in its composition. These drying powders serve to dry the seeds and enhance their flowability, facilitating improved mechanized sowing. The application process entailed manual handling with the aid of a resealable plastic bag measuring 14x20 cm. Seeds were placed into the bag along with 0.2 grams of each material, and then thoroughly stirred until all the drying powder adhered to the seeds (see Figure 1, scheme 3).

Laboratory tests and data collection

The germination tests were conducted according to the Instructions for Forest Seed Analysis [³⁵]. Seeds from control treatments (uncoated seeds - T1) and seeds subjected to coating treatments (T2, T3, T4, T5, T6, T7, T8) were placed in Petri dishes lined with two sheets of filter paper moistened with 2.5 times its mass in water. The plates were then placed in a BOD-type germination chamber with a constant temperature of 30°C and a 12-hour photoperiod. Moistening of the plates occurred twice a week, with 1 ml of distilled water being replaced each time.

The first count was conducted three days after installation and then repeated every three days until the end of the experiment (20 days). Seed germination was determined by the number of seeds emitting a radicle, in accordance with botanical criteria [⁴³,⁴⁴], which involved measuring radicle emission at 2mm. Twenty seedlings were sampled per treatment for measuring length of the shoot (Shoot), consisting of the epicotyl, hypocotyl, and cotyledons, as well as the length of the primary root (Root), in centimeters.

We calculated the germination percentage (%G) by the number of seeds that emit radicles to evaluate the relationship between coating techniques and seed quality. The germination speed index (GSI), a trait associated with seed vigor and field emergence [¹⁵], was used to evaluate the speed and uniformity of germination.

To compare the sensitivity of each species to the coating method, we calculated the ratio between the germination percentage of the coated seeds and the control (%Gtreat / %Gcontr), which we classified as follows: extremely sensitive (ES, < 0.25), sensitive (S, 0.26-0.50), low sensitivity (LS, 0.51-0.75), indifferent (I, 0.76-1.0), and potentiated (P > 1.0), according to Dutra and coauthors [²⁴].

Data analysis

We tested data normality using the Shapiro-Wilk test and residual plots. Before applying the one-way ANOVA, the homogeneity of variances was verified using Levene’s test. The ANOVA was complemented by Tukey’s post-hoc test to detect differences between treatments at a 5% significance level. Exploratory data analysis was conducted, including box plots for the analysed parameters (%G, GSI, primary root length, and shoot). All analyses were performed using R software (version 4.3.3) [⁴⁵].

RESULTS

Pelleting and film coating demonstrated comparable effects, with the magnitude of responses varying according to species, method, and coating material. For Guazuma ulmifolia, both pelleting and film coating had no detrimental impact on germination or initial seedling development, suggesting these methods are compatible with the physiological characteristics of the species (Table 3). The uncoated treatment (T1) exhibited the lowest variability in final germination percentage (%G) (Figure 2A), serving as a consistent baseline. Among treatments, only encapsulation (T6) significantly reduced germination (G = 18%), showing a strong statistical difference (F = 26.26; p =2 × 10^-16) in the proportion of germinated seeds, along with an increase in seed mortality (F = 95.69; p = 2 × 10^-16). Additionally, G. ulmifolia displayed extreme sensitivity (ES) to the encapsulation method, which negatively affected seedling development (Table 3).

Table 3
Mean and standard deviation (±) of the percentage of germinated seeds (%G), germination speed index (GSI. Average primary root length (Root) and shoot length (Shoot) in centimeters. Degree of sensitivity (S) and its classification (Class.) S: Sensibility. Class: Classification. ES: extremely sensitive. S: sensitive. LS: low sensitive. I: indifferent. P: potentiated. Equal letters in the same column show no significant difference following Tukey's test (p < 0.05).

Treatment1	%G	GSI	Root(cm)	Shoot(cm)	S	Class.
Guazuma ulmifolia
T1	84.1±12a	3.7±0.6a	2.15±0.64a	1.09±0.26a
T2	72.8±15.5a	3.3±0.9a	2.22±0.58a	1.15±0.24a	0.87	I
T3	76.7±14.8a	3.8±0.7a	1.92±0.66a	1.02±0.34a	0.92	I
T4	79±11.7a	3.4±0.6a	1.99±0.51a	1.11±0.28a	0.94	I
T5	64.1±16.1a	3.2±0.9a	1.7±0.73a	1.23±0.40a	0.76	I
T6	17.7±5b	0.5±0.1b	-	-	0.21	ES
T7	76.1±14.6a	3.4±0.8a	2.19±0.61a	1.02±0.24a	0.9	I
T8	77.7±12.2a	3.5±0.6a	2.05±0.28a	1.02±0.29a	0.93	I
Mimosa bimucronata
T1	70.4±9.1a	4.3±0.8a	0.87±0.4b	2.77±0.7a
T2	72;3±8.9a	4.6±0.6a	1.35±0.9b	3.11±0.5a	1.03	P
T3	67.3±9.3a	4.1±0.6a	2.96±1.1a	3.23±0.8a	0.96	I
T4	63±7.6a	3.9±0.5a	1.42±0.7b	3.03±0.8a	0.91	I
T5	72.1±7.8a	4.3±0.5a	1.79±0.6b	2.74±0.5a	1.03	P
T6	49.8±14.6b	1.9±0.6b	-	-	0.71	SB
T7	63.6±9.1a	4.1±0.6a	1.24±0.4b	2.95±0.6a	0.91	I
T8	75.6±9a	4.2±0.9a	1.41±0.5b	3.01±0.7a	1.09	P

• ¹
  T1 - Control, uncoated; Pelleting with different materials (T2 - coating mass; T3 - agricultural limestone; T4 - potassium silicate; T5 - agricultural gypsum); Encapsulation (T6 - sodium alginate + copper sulfate II) and Film coating with two materials (T7 - drying powder without finishing agent and T8 drying powder with graphite).

Figure 2
Boxplot of percentage germination (%G), germination speed index (GSI), Primary root length (Root) and shoot length (Shoot). A for Guazuma ulmifolia and B for Mimosa bimucronata. T1 - Control, uncoated; Pelleting with different materials (T2 - coating mass; T3 - agricultural limestone; T4 - potassium silicate; T5 - agricultural gypsum); Encapsulation (T6 - sodium alginate + copper sulfate II) and Film coating with two materials (T7 - drying powder without finishing agent and T8 - drying powder with graphite).

Although pelleting and film coating had no negative effects on germination, pelleting with potassium silicate (T4) resulted in the lowest variation in germination speed index (GSI) (Figure 2A), highlighting its potential to enhance uniformity. Pelleting with agricultural gypsum (T5) promoted a broader germination period, which can be advantageous for staggered seedling emergence. Encapsulation (T6) substantially reduced germination speed compared to all other treatments, being the only method that caused a significant delay (F = 22.7; p = 6.42 × 10^-16) (Table 3).

Root and shoot lengths were not significantly affected (Root: F = 1.657; p = 0.137; Shoot: F = 1.385; p = 0.225), indicating that most coatings maintained normal seedling development (Table 3). Although encapsulated seeds (T6) did not produce normal seedlings and were excluded from this analysis, film coating treatments (T7 and T8) promoted more consistent root growth (Figure 2A). The shoot also showed reduced variability in T7 (film coating with drying powder without finishing agent), suggesting greater uniformity in seedling establishment (Figure 2A).

For Mimosa bimucronata, both pelleting and film coating maintained high germination percentages and germination speed (Table 3). Notably, agricultural gypsum (T5) and film coating with drying powder (T7) resulted in the most uniform germination responses (%G and GSI) (Figure 2B). Treatments such as coating mass (T2) and both film coatings (T7 and T8) enhanced germination performance, highlighting their potential applicability in seed enhancement (Table 3). In contrast, encapsulation with sodium alginate and copper sulfate (T6) significantly reduced germination (F = 7.18; p = 1.66× 10^-06) and slowed germination speed (F = 17.74; p = 1.86 × 10^-13). This treatment also decreased the number of hard seeds (F = 2.413; p = 0.0282) while causing the highest seed mortality (F = 294.8; p = 2 × 10^-16) (Table 3). Nonetheless, M. bimucronata exhibited lower sensitivity to encapsulation than G. ulmifolia (Table 3), indicating some level of tolerance to this coating method.

Pelleting treatments significantly increased primary root length (F = 18.15; p = 2.57 × 10^-15), with limestone (T3) yielding the most substantial effect-tripling root length relative to the control (Table 3). Despite this marked improvement, T3 showed higher variability in root growth (Figure 2B). Shoot length did not differ significantly among treatments (F = 1.434; p = 0.206); however, greater uniformity in shoot development was observed in the agricultural gypsum treatment (T5) (Figure 2B). As with G. ulmifolia, the encapsulation treatment (T6) did not result in viable seedlings and was excluded from this part of the analysis.

DISCUSSION

Pelleting increases seed mass and size while standardizing shape, thereby enhancing seed handling and sowing precision in restoration practices [¹⁷,²⁰,⁴⁶]. This technique also confers mechanical resistance to radicle and cotyledon protrusion [⁴⁷]. Despite these structural modifications, our results indicate that pelleting did not impair the germination performance of either species evaluated. This finding aligns with previous studies showing that pelleting had no detrimental effect on Solanum sessiliflorum Dunal seeds [⁴⁶] and 20 pelleted Myrtaceae species [⁴⁶]. Furthermore, pelleting may confer additional advantages, such as protection against herbivory [⁴⁹] and improved emergence rates [⁴⁶], underscoring its potential value in direct seeding applications.

The pelleting material used (T2) consisted primarily of clay, a substance known for its excellent water retention and cation exchange capacities [⁵⁰]. These properties likely contributed to mitigating any physical barrier effects, allowing normal germination. In addition, pelleting with agricultural limestone (T3) significantly increased root length in Mimosa bimucronata, a desirable outcome for seedling establishment. This benefit can be attributed to the presence of CaO and MgO in limestone, which are essential for structural integrity, enzymatic activation, and chlorophyll synthesis in plants [⁵¹]. Moreover, limestone has been shown to enhance root biomass [⁵²] and promote the growth of native seedlings [⁵³], reinforcing its potential value; however, any benefits in field conditions remain unverified and require direct field evaluation. Nonetheless, this treatment exhibited greater variability in root growth (Figure 2B), which may influence field performance under heterogeneous conditions.

For direct seeding, ideal treatments should promote rapid and uniform germination, increase seedling vigor, and offer protection against environmental stressors and pathogens [¹⁸]. In this regard, pelleting with potassium silicate (T4) yielded the most consistent germination speed index (GSI) in Guazuma ulmifolia, indicating stable and reliable germination, an important attribute for field establishment (Figure 2A). Potassium silicate offers multiple agronomic benefits, such as improved potassium availability, reduced salinity compared to potassium chloride, and enhanced tolerance to drought and diseases due to its silicon content [⁵⁴-⁵⁶]. While it did not significantly increase germination percentage or vigor in the species tested, its stabilizing effect on germination dynamics suggests potential relevance for restoration, although these effects must be validated under field conditions.

Agricultural gypsum (T5) did not negatively affect germination or seedling growth in either species. Gypsum provides essential nutrients such as calcium and sulfur in the form of CaSO₄, which play critical roles in enzymatic processes and structural development [⁴⁹]. In G. ulmifolia, this treatment was observed to stagger germination over time under controlled conditions (Figure 2A). While this pattern may hypothetically reduce intra-specific competition or enhance establishment success, these potential benefits remain speculative and require field validation, particularly under variable environmental conditions. Early germination has been associated with reduced survival in the field [²⁶], suggesting that distributing emergence over time could be advantageous; however, such extrapolations from controlled experiments should be interpreted with caution. Additionally, T5 reduced variability in germination parameters (%G and GSI) and improved total germination for M. bimucronata, indicating its potential suitability for direct seeding strategies in controlled conditions. Future studies should evaluate these effects under field conditions to confirm translational relevance.

In contrast, the encapsulation method produced the most unfavorable outcomes, significantly reducing both germination and seedling vigor in both species, with G. ulmifolia being particularly affected. Alginate-based encapsulation may impair water uptake due to the slow rehydration of sodium alginate, which depends on electrolyte presence and environmental conditions [⁵⁷-⁵⁸]. Similar issues have been reported in other native species, where encapsulation resulted in up to a 60% reduction in germination compared to uncoated seeds [²⁴]. The inclusion of copper sulfate (CuSO₄) in the encapsulation matrix likely intensified these effects. Although Cu²⁺ contributes to antimicrobial protection and plays essential physiological roles [⁴⁰,⁵¹,⁵⁹,⁶⁰], excessive availability of this ion can induce osmotic stress and ionic toxicity. High external concentrations of Cu²⁺ may reduce the water potential around the seed surface, delaying imbibition, while intracellular accumulation of copper can disrupt membrane integrity, generate reactive oxygen species, and inhibit key enzymes involved in germination [⁶¹,⁶²]. These combined effects explain the pronounced decrease in germination and seed vigor observed in the CuSO₄ crosslinked treatments.

Given these findings, the use of Cu²⁺ as a cross-linking agent should be approached with caution in seed encapsulation protocols, particularly for sensitive native species. Alternative divalent cations, such as Ca²⁺, remain preferable for maintaining seed viability, while Cu²⁺ may be more suitable for applications emphasizing antimicrobial protection rather than germination enhancement. Drying powder-based film coatings (T7 and T8) are typically used in conjunction with bioactive compounds, such as protectants or growth regulators [¹⁷,⁶³]. These materials facilitate rapid and uniform drying, reducing seed stickiness and improving flowability during sowing [²³,⁶⁴]. Although some studies suggest drying powders may reduce seed vigor in major crops [64,65], our findings show no adverse effects on either germination or seedling development in the native species tested. In fact, T7 promoted more uniform root growth and reduced variability in shoot development (Figure 2B), contributing to more predictable seedling performance under controlled conditions.

Among the treatments tested, pelleting with limestone (T3) consistently improved root development in M. bimucronata, which could theoretically benefit establishment, although such effects remain hypothetical and require field testing. Conversely, the film coating with drying powder (T7) promoted uniform seedling morphology, suggesting greater developmental stability. These complementary effects point to the potential of combining pelleting materials and coating strategies to maximize both performance and reliability in seed-based restoration.

Overall, most coating treatments tested did not negatively affect germination responses in either species. The exception was encapsulation, which proved unsuitable due to its detrimental effects on germination and seedling vigor. On the other hand, the beneficial impacts observed, such as increased root length (T3), reduced variation in germination and growth (T4, T5, T7), and enhanced emergence stability demonstrate the potential value of seed coating technologies, though their actual effectiveness in restoration settings requires field validation. While these treatments did not universally enhance germination rates, they contributed important functional traits (e.g., emergence uniformity, root development) that are critical for successful seedling establishment.

Although our findings provide important insights into the physiological responses of coated seeds under controlled conditions, the study did not include field trials, which limits extrapolation to restoration contexts. Environmental variability, seed soil interactions, and biotic pressures may alter treatment performance. Future research should therefore evaluate these seed coating materials under field conditions, quantifying emergence, early survival, and establishment to determine their practical relevance for large-scale ecological restoration.

CONCLUSION

Seed coating techniques, particularly pelleting and film coating, showed potential for modulating germination timing and improving certain aspects of seed performance. In Mimosa bimucronata, treatments involving potassium silicate, agricultural gypsum, and limestone, as well as film coating with drying powder, contributed to better seedling development and vigor. For Guazuma ulmifolia, however, the differences among treatments were less pronounced, and the control treatment often exhibited comparable or superior results. These findings suggest that the effectiveness of coating materials is species-dependent and may vary according to specific physiological responses. Therefore, while some materials present promising potential, especially for small-seeded species like M. bimucronata, their use in restoration programs should be carefully tailored to the target species and site conditions.

• Funding:
  The study was funded by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES - Financial Code 001).
• Institutional Review Board Statement:
  Not applicable
• Informed Consent Statement:
  Not applicable.

Acknowledgments:

The authors wish to thank the Seeds and Forest Seedlings Laboratory (LASEM-UFSCar) for supporting the development of this research and AES Brasil for kindly donating the seed lots used in the experiments, and the financial support, the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the scholarship.

Use of Generative Artificial Intelligence

The authors declare that large language models and other generative artificial intelligence (AI) or AI-assisted technologies cannot be credited as authors and have not been listed as authors of this paper.

The authors declare that generative artificial intelligence (AI) or AI-assisted tools were used under full human supervision. The tool(s) and version(s) used, and their purpose, are described here: grammar correction, punctuation correction, and synonym suggestion. No confidential or sensitive data were uploaded to such tool(s), and all AI-assisted content was checked, corrected and approved by the authors, who take full responsibility for the integrity and originality of the manuscript.

Data Availability Statement:

Research data are available in the body of the manuscript.

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Edited by

• Editor-in-Chief:
  Bill Jorge Costa

• Associate Editor:
  Oriel Tiago Kölln

Publication Dates

• Publication in this collection
  17 Aug 2026
• Date of issue
  2026

History

• Received
  07 Dec 2025
• Accepted
  26 May 2026