Aluminum Stress Stimulates Growth in Phyllostachys edulis Seedlings: Evidence from Phenotypic and Physiological Stress Resistance

Abstract

The exacerbation of Aluminum (Al) toxicity is a leading cause of forest degradation. However, the effects of Al on clone bamboo are not well-characterized. This study examined the influence of Al on bamboo growth using one-year-old Phyllostachys edulis seedlings subjected to control Al treatments, which aim to provide theoretical support for improving the soil quality of bamboo forests. The results indicated that the Al content in the seedlings increased by 86.42% to 162.79% compared to the control. However, it remained within a relatively stable range, with the root being the primary site of accumulation. Among the treatments, the 0.3 mM Al group (Al³⁺) exhibited the highest values in biomass indexes (LB, RB and AGB). In contrast, the 2.0 mM Al treatment led to a significantly higher root-to-shoot ratio (RSR) than other groups. Physiological analyses revealed coordinated responses in key antioxidant enzymes (POD, SOD, CAT) and osmotic adjustment substances (Pro, SP, Bet). These findings demonstrate that P. edulis possesses considerable tolerance to Al, with a significant phenotypic inhibitory effect that was not observed with 2.0 mM Al treatment. Bamboo responds to Al stress through controlling Al absorption, optimizing resource reallocation, and enhancing adaptability physiology capacity, illustrating a comprehensive collaboration adaptive mechanism.

1. Introduction

Acidic soil is widespread in tropical and subtropical regions and is considered a major factor in the decline of agricultural and forest land productivity [1,2,3,4], with direct implications for crop yield and food security [5,6]. Beyond natural climatic influences, intensive agricultural practices—such as excessive fertilizer application, monocropping, and overgrazing—significantly contribute to accelerated soil acidification [7,8]. When the soil pH value is lower than 5.0, abundant solid aluminum minerals such as aluminosilicates and oxides in the earth’s crust will dissolve into toxic forms, such as Al (OH)²⁺, Al³⁺, Al (OH)₂⁺ and Al (OH)₄⁻ [1,4,9,10]. These ions become mobile in the soil solution, are taken up by plants, and accumulate to toxic levels [11]. Among them, the trivalent Al³⁺ is the most phytotoxic, inhibiting plant growth and reducing productivity. Aluminum toxicity is recognized as a major limiting factor for crop cultivation in acidic soils. Globally, over 40% of soils are affected by Al toxicity due to progressive acidification [9]. As a result, understanding the mechanisms and effects of Al-induced phytotoxicity has become a central research theme in agricultural ecology and soil chemistry.

Aluminum (Al) is not an essential nutrient for plants and does not participate in any vital metabolic processes within living organisms [4]. Nevertheless, Al has been shown to exert beneficial effects on the growth and development of certain plant species, such as Camellia spp. and Symplocos paniculata [12,13,14]. Some studies indicated that Al could enhance phosphorus uptake, increased biomass, improve photosynthetic performance, and elevate leaf gas exchange rates in these plants [15]. However, a number of studies demonstrated the toxic effects of Al on most plant species [16,17]. For instance, soil acidification reduced microbial activity and slowed the decomposition of organic matter [18]. The accumulation of aluminum on the cell walls of root tips is a prerequisite for aluminum toxicity. By means of combing with negative ions on the cell walls, it disrupted the Ca²⁺ channels of the root protoplasmic membrane, affecting its information transmission [19,20], which would further alter the structure and function of the root cell protoplasmic membrane (affecting enzyme activity, disrupting the cytoskeleton, etc.) [21]. In addition, the binding of Mg²⁺ on the root apoplast was inhibited, which reduced the absorption of Mg [22,23]. Differences in the capacity for physiological and metabolic regulation reflect interspecific variations in plant tolerance to Al toxicity.

Aluminum toxicity also inhibits root growth, impairs nutrient uptake, and reduces photosynthetic efficiency [24]; therefore, the role of Al in plant physiology cannot be simplistically categorized as solely negative or positive; it is highly dependent on the Al tolerance of plant and physiological regulatory mechanisms. Under aluminum (Al) stress, the reactive oxygen species (ROS) concentration in plants increases, leading to membrane lipid peroxidation and an elevation in osmotic potential. This process exacerbates toxic effects. In response, plants enhanced antioxidant enzyme activity to scavenge ROS, maintained metabolic balance, and actively accumulated solutes to increase cell sap concentration. These adaptations improved the plant ability to uptake inorganic nutrient ions and retain water, thereby enhancing cellular stress tolerance [14,16,24]. Furthermore, when exposed to aluminum stress, plant roots can secrete various organic acids (malate, citrate, and oxalate) to form insoluble complexes with aluminum ions in the rhizosphere, thereby preventing their absorption [16]. This inhibitory mechanism is established within minutes after some plants come into contact [25,26], but the chelating ability of the secreted organic acids for aluminum ions varies depending on the type of organic acid, the plant species, and the age of the plant [20,27]. Differences in the capacity for physiological and metabolic regulation reflect interspecific variations in plant tolerance to Al toxicity.

Bamboo is one of the most important non-wood resources in the world, and it is widely distributed in acidic red-soil regions of tropical and subtropical areas [28]. Compared to other economic species, bamboo has advantages such as fast growth rate, rapid biomass accumulation, and well-developed rhizomes. However, long-term unreasonable fertilization has led to increased acidification of bamboo forests and an increase in active aluminum, causing bamboo forests to be poisoned by aluminum and becoming one of the important reasons for the decline of bamboo forests [29,30]. For instance, in a Phyllostachys praecox plantation amended with rice husk mulch for 15 years, soil pH decreased from 5.57 to 3.20 [31,32], and the pronounced acidification was primarily attributed to the release of organic acids from decomposing organic amendments and root exudates [33], which led to a significant observable increase in extractable aluminum (Al) fractions in long-term mulched P. praecox soils, leading to substantial Al accumulation in roots and subsequent inhibition of nutrient transport. Moreover, intensive management practices had been linked to reduced soil organic carbon pools, diminished microbial activity [18,34,35], and leaching of exchangeable base cations [36], ultimately resulting in declining bamboo shoot and timber quality and yield [37]; Gui et al. [38] demonstrated that the moso bamboo (P. edulis) seeds germination was inhibited by 2.0 mM. Despite these findings, which had predominantly focused on soil biochemical processes under Al toxicity and its impact on bamboo growth, there remains a scarcity of studies quantifying Al toxicity in bamboo and elucidating the corresponding physiological response strategies. This study employed P. edulis seedlings in an Al addition experiment to investigate growth and physiological responses to aluminum exposure. This study aims to (1) reveal the absorption characteristics of aluminum by P. edulis and its relationship with the gradient of external aluminum concentration, and attempt to explore the threshold value of aluminum for bamboo growth; (2) elucidate whether and how phenotypic plasticity, physiological enzyme activities, and osmotic adjustment substances in P. edulis seedlings exhibit a coordinated response to aluminum stress in order to provide a theoretical basis for rehabilitating bamboo forest soils and supporting sustainable management practices.

2. Materials and Methods

2.1. Study Area

The study was conducted in a greenhouse at the Changsha Forestry Seedling Center (113°02′30″ E, 28°18′54″ N); the greenhouse was covered with transparent plastic film to ensure that the treated individuals had a consistent environment, and the temperature is controlled below 35 °C by an automatic ventilation system.

The site is characterized by an elevation ranging from 50 to 108 m, with slopes less than 15°. It is located within a humid subtropical monsoon climate zone, with a mean annual temperature of 17.5 °C, an average annual precipitation of 1378 mm, a mean annual relative humidity of 81%, and total sunshine duration of 1814.8 h per year.

2.2. Experimental Design

One-year-old container-grown P. edulis seedlings with an average height of 93.3 cm ± 4.12 cm and an average stem diameter of 1.24 cm ± 0.05 cm were selected for this study. All seedlings were healthy, free from pests and diseases, and exhibited uniform growth, and the substrate consisted of a 8:2 mixture of peat and yellow-brown soil with pH 4.8; within the mean content, the organic matter was 413.7 g kg⁻¹, the TAl (total Al content) and Ex-Al (exchangeable Al) were 39.12 g kg⁻¹ and 92.94 mg kg⁻¹, the mean value of TN (Total nitrogen content) and TP (Total phosphorus content) were 11.05 g kg⁻¹ and 0.41 g kg⁻¹, respectively.

An aluminum solution was prepared using Al₂(SO₄)₃·18H₂O, which could release Al³⁺ with hydrolyzation [39], and five concentration gradients were established with 0, 0.05, 0.3, 0.7, 2.0 mM (abbreviation of mmol L⁻¹); therein, a pure water treatment served as the bank control (0 mM), the concentration gradient was selected based on our preliminary experiments, and the concentration of 0.05 mM was chosen to trigger early stress signals and physiological responses in young bamboo seedlings without causing significant growth retardation. The concentrations from 0.3 mM–0.7 mM targeted the key response ranges of root physiology and phenotype of the standing bamboo to aluminum stress, and the concentration of 2.0 mM represented the possible saturated stress concentration level that might be triggered. Each treatment gradient had three repetitions, and 30 pots (30 cm diameter × 28.5 cm height) as samples were allocated per repeating group, i.e., 90 pots were assigned to each treatment. All the groups were arranged with random block arrangement in the greenhouse. Each sample received 500 mL of the corresponding solution each time, and the solutions were applied evenly and slowly to the soil of the container seedlings to allow complete absorption by the substrate. Treatments were administered every 5 days over a total experimental period of 28 days, which is deemed adequate to evaluate the impact of aluminum on moso bamboo seedlings while avoiding confounding effects associated with prolonged or severe toxicity.

2.3. Sample Treatment

After the treatment period, 10 samples were randomly selected from each repeating group. The samples were rinsed with deionized water to remove surface soil and impurities, and then separated into roots, stems, and leaves using pruning shears. After air-drying to remove surface moisture, the fresh weight was recorded. After being dried in the air, root systems were divided into non-overlapping parts by scissors, and then root length (RL) was measured using Image J (v1.54f; National Institutes of Health, Bethesda, MD, USA). All plant parts were then oven-dried at 105 °C until constant weight was achieved. Leaf biomass (LB), stem biomass (SB), and root biomass (RB) were weighed, and the above-ground biomass (AGB) was the sum of LB and SB, root-to-shoot ratio (RSR) was calculated with RB/AGB, and specific root length (SRL) was calculated by RL/RB. Finally, the organ samples were ground and sieved (0.25 mm), and stored in a drying vessel for aluminum content analysis.

Besides that, the other 3 plants were randomly selected from each group for physiological indexes. In each sample, the 5–8 fully expanded and undamaged root systems from the basal of stem, which were basically in the same vertical position, were collected and immediately frozen with liquid nitrogen, then wrapped in self-sealing bags and stored at −40 °C. 0.1 g per sample was washed, cut into pieces, and ground into a homogenate in a pre-chilled mortar with 1.6 mL of 50 mM cold phosphate buffer (pH = 7.8) in an ice bath. The homogenate was centrifuged at 12,000 r min⁻¹ for 20 min at 4 °C in a KH20R-II centrifuge (Xinlin Corp., Gongyi, China), and the supernatant was collected as the crude enzyme extract. The supernatant of the sample was used to analyze the antioxidant compounds’ (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT)) activity, and the preparation methods of the measured liquids of osmotic adjustment substances (free proline (Pro), soluble protein (SP) and Betaine (Bet)) and MDA referred to the studies by [40,41,42].

2.4. Sample Analysis

After microwave digestion of the organ samples, the aluminum contents (TAl, mg kg⁻¹) were determined by inductively coupled plasma mass spectrometry (ICP-MS, thermoelectric X-Series 2) [33]. AN ultraviolet and visible spectrophotometer (UV-3600i Plus, Shimadzu Corp., Kyoto, Japan) was used to identify the physiological metabolic indicators except for Betaine (Bet); therein, superoxide dismutase (SOD) activity (U g⁻¹ FW) was determined using the nitrobluetetrazolium reduction method; peroxidase (POD) activity (U mg⁻¹ FW) was measured via the guaiacol method; and catalase (CAT) activity (nmol min⁻¹ g⁻¹ FW) was assayed by ultraviolet absorption [40]. Malondialdehyde (MDA) content (nmol g⁻¹ FW) was measured using the thiobarbituric acid (TBA) method. Soluble protein (SP) content (mg g⁻¹) was determined via the Coomassie brilliant blue method. Free proline (Pro) content (μg g⁻¹ FW) was assessed using ninhydrin colorimetry [41]. Soluble sugar (SS) content (mg g⁻¹ FW) was measured using the anthrone–sulfuric acid method. Betaine (Bet) content (mg g⁻¹) was quantified through LC-20A high-performance liquid chromatography (HPLC) (Shimadzu Corp., Kyoto, Japan) [42].

2.5. Statistical Analysis

All data were subjected to a homogeneity of variance test before implementing the specific statistical analysis procedures to meet the prerequisite assumptions for the subsequent analysis. For comparing the Al content in same bamboo organ among additive gradients or the various organs in each additive gradient, the mean values of three replicates were used for analysis with one-way ANOVA. Least significant difference (LSD) was used to examine the differences among gradients if the difference was significant. For correlation analysis between morphological/physiological indicators and aluminum content in P. edulis, a Shapiro–Wilk normality test on the continuous variables involved was conducted before correlation analysis, the results showed that their distributions significantly deviated from normality (p < 0.05), so the Spearman correlation analysis was further conducted. Statistical analyses, including one-way ANOVA, multiple comparisons using the LSD test, and Spearman correlation analysis, were performed with SPSS (v21.0, IBM Corp. Armonk, NY, USA). Figures were generated using Origin (v2021, OriginLab Corp., Northampton, MA, USA).

3. Results

3.1. Comparison of Aluminum Content in P. edulis Seedlings Among Treatments

The mean values of total aluminum (TAl) content in the seedlings ranged from 42.92 to 60.51 mg kg⁻¹ across Al treatments (Figure 1), with the relative ratio of Al absorption to Ck increasing by 86.4% to 162.8%. No significant differences in TAl content were observed among the aluminum-added treatments; however, they were all significantly higher than the Ck (p < 0.05). The TAl content did not exhibit a concentration-dependent increase with higher aluminum application; therein, the TAl content of the leaf was from 20.13 mg kg⁻¹ to 28.95 mg kg⁻¹, root content was from 80.41 mg kg⁻¹ to 121.3 mg kg⁻¹, and the content of shoot was from 4.13 mg kg⁻¹ to 4.87 mg kg⁻¹. A comparison of TAl content among organs revealed that the root system accumulated significantly higher amounts of aluminum than the stems and leaves (p < 0.001). No significant difference was detected between stems and leaves. The order of TAl accumulation was root > stem > leaf, indicating that aluminum was primarily concentrated in the root system.

3.2. Differences in Growth Traits of P. edulis Seedlings with Aluminum Addition

The significant differences in LB, RB, RL, SRL, RSR, and AGB were observed between treatments and Ck (

Table 1. The comparison of the seedling traits of P. edulis among treatments. n = 10. The data in the table are presented by mean value ± standard errors. ** denotes the significant difference in treatments, *** denotes the highly significant difference in treatments (p < 0.001), lowercase letters indicate the significant differences between treatments with 95% confidence interval analysis. LB (leaf biomass); SB (stem biomass); RB (root biomass); AGB (above-ground biomass); RSR (root–shoot ratio); RL (root length); SRL (specific root length).

Treatment	LB (g)	SB (g)	RB (g)	AGB (g)	RSR	RL (g)	SRL (cm/g)
Ck	1.71 ± 0.02 d	4.31 ± 0.22 c	4.75 ± 0.14 e	6.02 ± 0.24 b	0.79 ± 0.01 c	20.52 ± 1.05 c	4.32 ± 0.14 a
Al1	2.16 ± 0.45 cd	3.54 ± 0.23 d	10.72 ± 0.09 d	5.7 ± 0.68 b	1.9 ± 0.21 a	21.89 ± 0.66 Bc	2.04 ± 0.04 b
Al2	3.66 ± 0.02 a	5.0 ± 0.29 b	18.38 ± 0.21 a	8.66 ± 0.31 a	1.43 ± 0.03 b	24.76 ± 1.09 a	1.35 ± 0.06 d
Al3	2.36 ± 0.25 c	4.08 ± 0.15 c	11.92 ± 0.41 c	6.44 ± 0.4 b	1.85 ± 0.05 a	24.21 ± 0.73 ab	2.03 ± 0.02 b
Al4	3.02 ± 0.31 b	5.9 ± 0.12 a	12.51 ± 0.2 b	8.92 ± 0.43 a	1.4 ± 0.05 b	22.72 ± 0.79 b	1.82 ± 0.05 c
F values	24.583	55.332	1259.0	36.335	59.7	11.471	697.73
p values	<0.001 ***	<0.001 ***	<0.001 ***	<0.001 ***	<0.001 ***	0.001 **	<0.001 ***

). Specifically, LB, RB, RL, and RSR were significantly higher in aluminum-treated seedlings than in Ck (p < 0.001), whereas SRL was significantly higher in Ck than in all treatments (p < 0.001). Among these, 0.3 mM treatment resulted in the highest values of LB, RB, and AGB, which were significantly greater than those in other treatments (p < 0.01). Meanwhile, 2.0 mM had the highest RSR, which was also significantly greater compared to other treatments (p < 0.001).

3.3. Physiological Responses of P. edulis Seedlings Under Aluminum Treatment

Among the treatments, significant differences were observed in antioxidant enzyme activities and osmotic regulation indices (p < 0.001) (Figure 2). Among the antioxidant enzymes, SOD activity initially decreased and then increased with rising aluminum concentration, while CAT and POD activities initially increased and then decreased, reaching their peak values at 0.3 mM. In contrast, SP content showed a gradual decreasing trend. Regarding osmotic regulators, MDA and SS contents generally increased first and then decreased, with maximum values observed at 0.3 mM and 0.05 mM, respectively. In comparison, Pro and Bet contents decreased with increasing aluminum concentration.

3.4. Correlation Between Morphological/Physiological Indicators and Aluminum Content in P. edulis

Analysis of the relationship between morphological and physiological indicators and TAl content (Figure 3 and Figure 4), revealed that aluminum concentrations in LTAl, STAl, and RTAl were positively correlated with organ biomass (LB, SB, RB), root-to-shoot ratio (RSR), and root length (RL), but negatively correlated with SRL. These results indicate that the addition of aluminum promotes biomass accumulation and root growth in the seedlings. Regarding physiological responses, aluminum content showed a non-significant inhibitory effect on SOD activity, while non-significant promoting effects were observed on POD and CAT activities.

4. Discussion

4.1. Spatial Distribution of Aluminum in P. edulis and Its Effect on Phenotype

Aluminum is dissolved into various toxic free ions at pH below 5.0 and absorbed by plants through root hairs [43]. This study found that the root system is the main site of aluminum accumulation (Figure 1), consistent with findings in P. praecox, Cunninghamia lanceolata, and Camellia spp. [14,44]. This study also revealed a spatially heterogeneous distribution of aluminum in one-year-old P. edulis seedlings, with concentrations gradually decreasing from the bottom to the top, which partially reflected the impact of aluminum on growth according to prolonged aluminum toxicity which reduces nutrient transport capacity in bamboo roots, leading to decreased aluminum content in stems, branches, and leaves [45]. Furthermore, the aluminum content in the seedlings did not increase with higher external aluminum concentrations but remained within a relatively stable range (mean values of 42.92–60.51 mg kg⁻¹), consistent with the results reported by the previous studies [33,38,39,40,41,42,43,44,45,46], which suggested that P. edulis maintained a possible internal metabolic regulation for aluminum, although the precise mechanisms remain unclear. However, the present study showed (Table 1) that even at 2.0 mM, aluminum significantly promoted phenotypic traits except for specific root length (SRL). The decreasing SRL could be attributed to a lower growth rate of root length (RL) relative to root biomass (RB). The decrease in SRL reflected the decoupling between root length and biomass growth rate. Aluminum triggered physiological and growth adaptive changes in the roots. Under aluminum stress, the elongation of the most aluminum-sensitive fine roots were strongly inhibited, which may correspondingly promote thickening of root diameter and cell walls [8]. Meanwhile, aluminum stress disrupted the balance of plant hormones: the transport and signaling of auxin (IAA), which promoted elongation, was hindered, while the synthesis of hormones that promote thickening and lignification (such as ethylene and jasmonic acid) increased [20], which would reduce the investment in biomass, and such morphological changes reflect the shift in the growing strategy of moso bamboo from a “pioneering” type to a “conservative” type. However, it appeared to be inconsistent with previous studies [47], indicating that aluminum concentrations of up to 2.0 mM did not cause significant toxicity in P. edulis seedlings but stimulated growth instead, likely due to external stress. The increase in root-to-shoot ratio (RSR) further suggested that, under aluminum stress, resources are allocated preferentially to root growth (e.g., biomass and length), which might be to enhance mineral nutrient absorption (e.g., phosphorus and carbon) [15,48]. Thus, we concluded that P. edulis responds to aluminum stress through dynamic resource allocation between growth and defense, along with structural adaptability remodeling.

4.2. Physiological Responses of P. edulis to Aluminum Stress

Under prolonged aluminum stress, plants activate external exclusion or internal tolerance to mitigate aluminum toxicity [49,50]. In our study (Table 1), aluminum was absorbed and maintained within a certain concentration range, which aligned with the internal tolerance strategy. As Figure 3 showed, the three major antioxidant enzymes—SOD, CAT, and POD—exhibited non-uniform responses. SOD activity increased rapidly with rising aluminum concentration, while CAT and POD activities initially increased and then decreased. This pattern reflects a coordinated response among antioxidant enzymes in P. edulis. Under aluminum stress, the seedlings produced a large amount of superoxide anion radicals, which rapidly induced higher SOD activity to maintain reactive oxygen species (ROS) homeostasis [51]. During the early stages of aluminum exposure, CAT and POD were promptly induced to counteract transient accumulation of H₂O₂ and enhance physiological function through promoted lignin synthesis. However, excessively high aluminum concentrations significantly suppressed CAT and POD activities [52], leading to their subsequent decline. Furthermore, under pot-based experimental conditions with limited nutrient resources, plants prioritized fundamental defense mechanisms such as SOD, while reducing enzymes like POD and CAT [53].

With increasing aluminum concentration, Pro, SP, and Bet decreased (Figure 2 and Figure 3), which played crucial roles in maintaining cellular osmotic balance and protecting plasma membrane integrity under environmental stress [54]. The decline in Pro and SP might mean a metabolic shift involving carbon and nitrogen reallocation as part of the stress response. The reduction in Bet may indicate a transition in choline metabolism toward the synthesis of membrane-protective compounds. Previous studies have shown that rapid growth, lignification, and protective barrier construction in P. edulis consume substantial amounts of SP and Pro [55]. Additionally, aluminum-induced root exudation of citrate—an Al³⁺ chelator—inhibited the synthesis of Pro and Bet [48], reflecting complex regulatory physiology in response to aluminum. Malondialdehyde (MDA) is an important indicator for characterizing the severity of oxidative damage in plants. As shown in this article, the addition of Al to the soil caused significant oxidative damage to the seedlings of P. edulis, but this damage did not continue to increase with the increase in concentration. Instead, it decreased after 0.3 mM. And MDA largely returned to control levels at 2.0 mM treatment. Combined with the changes in the phenotypic traits of P. edulis seedlings, this further indicated that the antioxidant enzymes represented by SOD played a key role in this process. The lack of significant correlation between aluminum accumulation and the activities of antioxidant enzymes or osmotic regulators (Figure 4) further supported the high aluminum tolerance of one-year-old P. edulis seedlings. The variation in soluble sugar (SS) content was generally consistent with antioxidant enzyme activity. SS dynamics reflect membrane lipid peroxidation stress and act as important signaling molecules that regulate metabolic and physiological processes, thereby activating antioxidant mechanisms in response to stress [56]. Overall, the results demonstrated that P. edulis responds to aluminum stress by enhancing its internal antioxidant capacity and osmotic regulation in a concentration-dependent manner.

4.3. Analysis of Aluminum Tolerance in P. edulis

Although numerous studies have reported the toxic effects of aluminum (Al) on plants, these effects typically become significant only beyond a critical concentration threshold [57,58]. Many Al-sensitive plants exhibit damage at very low concentrations; for example, 40–60 μmol L⁻¹ Al can harm barley (Hordeum vulgare) roots, and 50 µM Al inhibits root growth in Eleusine coracana [59]. In contrast, tea plants (Camellia spp.), which are typically Al-tolerant, show promoted accumulation of nutrients such as polyphenols and amino acids even at Al concentrations as high as 5.0 g L⁻¹ [46,60]. A low Al concentration of 0.3 mM stimulated root biomass accumulation in Tabebuia chrysantha seedlings, whereas a high concentration (2.4 mM) caused inhibition. The critical Al tolerance concentrations for Triticum aestivum, Zea mays, and Glycine max were reported as 40, 48, and 52 mM, respectively [61], while the toxicity threshold for root growth in tomato seedlings was 1.25 mM [62]. In our study, growth traits of one-year-old P. edulis seedlings remained higher than those of the control even at 2.0 mM Al, suggesting that the toxicity threshold for these seedlings exceeds this concentration. Therefore, it is concluded that one-year-old P. edulis exhibits relatively high aluminum tolerance compared to many other plant species. However, due to inconsistencies in the age of plant materials across studies, effective interspecific comparisons of Al tolerance remain challenging.

Within the Al concentration range of 0–2.0 mM, aluminum significantly promoted both module biomass and root phenotypic traits in one-year-old P. edulis seedlings (Table 1). Only the specific root length (SRL) in the control group was significantly higher than in Al-treated groups. The reduction in SRL was associated with a relatively lower growth rate in root length compared to root biomass. Most phenotypic indicators were highest under the 0.3 mM Al treatment, suggesting that the concentration might be a critical threshold for one-year-old seedlings. Nevertheless, the Al concentrations applied in this study did not induce significant toxicity. Other studies have reported that Al concentrations as low as 0.2 mM inhibit seed germination and growth in P. edulis [38,63]. Additionally, Li et al. [64] found that exchangeable Al in soil of up to 200 mg kg⁻¹ did not cause toxicity in P. praecox forests, though bamboo shoot production was significantly suppressed. These findings indicate that aluminum tolerance in P. edulis increases with age. It should be noted that current research on aluminum toxicity and tolerance has predominantly focused on seedlings and herbaceous plants, with limited studies on large herbaceous and woody species. Besides that, our study also had some limitations; for instance, the comparison on the various age of bamboo to aluminum stress, and the experiment duration should be extended to observe root development better, etc., and the underlying mechanisms and broader implications remain to be further elucidated.

5. Conclusions

This study reveals that moso bamboo (Phyllostachys edulis) exhibits heterogeneity in aluminum absorption across different spatial organs of standing culms, with the highest accumulation observed in the root system. It further demonstrates that aluminum supplementation stimulates growth-related plant traits, while indicating that aluminum concentrations of up to 0.2 mM do not exert significant stress on one-year-old moso bamboo. However, as a potent environmental signal, aluminum triggers physiological and growth adaptations in roots, shifting their strategy from a “pioneering” growth mode to a “conservative” survival approach. In response to aluminum stress, moso bamboo employs mechanisms, including regulated aluminum uptake, optimized resource reallocation, and enhanced osmotic and stress-resistant physiological efficiency, reflecting a comprehensive synergistic adaptation mechanism to aluminum stimulation. These insights into species-specific aluminum tolerance mechanisms contribute to a deeper understanding of moso bamboo’s adaptation to acidified soils and may inform sustainable bamboo forest management practices.