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Effects of aluminum on metabolism of reactive oxygen species and reactive nitrogen species in root tips of different Eucalyptus species

BMC Plant Biology volume 25, Article number: 55 (2025) Cite this article

Abstract

On acidified soil, the growth of Eucalyptus is seriously restricted by aluminum (Al) stress. Therefore, breeding Eucalyptus species with excellent Al tolerance, developing the genetic potential of species, and improving tolerance to Al stress are important for the sustainable development of artificial Eucalyptus forests. By observing the occurrence and distribution of the main reactive oxygen species (ROS) and reactive nitrogen species (RNS) in root tips of Eucalyptus seedlings under Al stress, this study analyzed change in the growth and physiological indexes of Eucalyptus seedlings under Al stress. The antioxidant enzymes activities of the root tips of different Eucalyptus species induced by Al stress resulted in different ROS and RNS contents, ultimately resulting in differing degrees of membrane lipid peroxidation. In addition to suppressions of root relative elongation and root activity, the accumulations of soluble sugar, soluble protein, and proline can be used as indicators of Al sensitivity in Eucalyptus species. This may be an important determinant of the differences in Al tolerance among Eucalyptus species. The accumulation of ROS and RNS in the roots of E. grandis and E. tereticornis resulted in severe oxidative and nitrification stress. The tolerance of E. urophylla and E. urophylla × E. grandis to Al stress was stronger than that of E. grandis and E. tereticornis. Differences in Al toxicity tolerance were related to long-term selection of the original habitat of the species; moreover, the Al tolerance was hereditary. Eucalyptus urophylla × E. grandis had stronger Al tolerance than its parents, which is indicative of heterosis. These results provide theoretical support for the breeding of tree species in areas with acidic soil.

Key message

In addition to suppressions of root relative elongation and root activity, the accumulations of soluble sugar, soluble protein, and proline can be used as indicators of aluminum (Al) sensitivity in Eucalyptus species. The Al tolerance of E. urophylla × E. grandis was better than that of both parents, which may have been due to heterosis.

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Introduction

Plantations are an important part of the terrestrial ecosystem, and have high ecological and economic value [1, 2]. About 30% of the world’s land area is currently acidic (pH < 5.5) due to anthropogenic and natural soil acidification process [3]. Soil acidification in plantations leads to the leaching of nutrient elements in soil with basal ions, resulting in a substantial loss of soil nutrients in the plantation and a serious decline in its fertility [4]. Aluminum (Al) is the most abundant metal element in the Earth’s crust, and mostly exists in Al-containing minerals in fixed states such as silicate or oxide [5]. However, Al is easily dissociated into Al3+ in acidic soil, which disrupts normal operation of the plant antioxidant system and restricts plant growth and development. Aluminum toxicity has become one of the most important causes of forest decline on acidic soils [6]. In recent decades, the degradation of plantations in area with acidic soil has severely restricted forestry production and damaged the ecological environment [7]. Root growth is highly sensitive to Al stress [8]. Under Al stress conditions, the redox state in plants breaks down, which usually manifests as rapid accumulation of various reactive oxygen species (ROS), such as superoxide free radicals (O2−), hydrogen peroxide (H2O2), hydroxyl radicals (OH−)and singlet oxygen (1O2) [9,10,11,12]. The levels can exceed the range of plant self-regulation, resulting in oxidative damage to plant cells or tissues. Excess accumulation of reactive nitrogen species (RNS) under stress condition can lead to nitrification stress, which can harm the plants [13, 14]. Both ROS and RNS play an important role in the plant response to stress; both induce toxic and protective effects on cells, i.e., they harm cells at high concentrations and act as signaling molecules at low concentrations [15, 16]. Under stress conditions, plant proline, soluble sugar, and soluble protein control the homeostasis of intracellular ions and regulate their translocation by osmoregulation [17]. Under Al stress, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, antioxidant enzyme activity and osmotic regulatory substances index will change to enhance the Al tolerance of Eucalyptus.

Eucalyptus is the general name of the Eucalyptus species in the Myrtaceae family, which contains about 800 species. It is native to the Australian mainland, although there are a few occurrences in the neighboring areas of New Guinea, Indonesia, and the Philippines [18]. Eucalyptus plantations are an important part of the world’s plantation industry and are playing an increasingly important role in wood supply and climate change [19]. Many countries in tropical and subtropical regions are vigorously developing Eucalyptus plantations and the global area of Eucalyptus plantations is increasing. The global area of Eucalyptus plantations covers > 25 million ha, thereby accounting for 15% of the world’s plantation area [20, 21]. Eucalyptus species have become the main fast-growing timber species in south China due to their strong adaptability, fast growth and production of useful materials; they account for a large proportion in wood production. Populus is widely planted in the north China, they are called “Eucalyptus in Southern and Poplar in Northern” [20]. In recent years, soil acidification caused by continuous industrialization, continuous cropping of plantations, and the application of chemical fertilizers has exacerbated Al stress and seriously affected the growth of Eucalyptus [3, 22,23,24]. Therefore, it is important to maintain the productivity of Eucalyptus plantations by selecting excellent Eucalyptus varieties with Al tolerance, fully exploiting the genetic potential of excellent varieties and improving the tolerance of Eucalyptus to Al stress. Current studies have found that Eucalyptus root tips mainly respond to Al stress by accumulating and secreting some substances (including lignin and callose, oenothein B, organic acids, etc.), which can enhance the cell wall defense ability, reduce root absorption of metals, and discharge heavy metal pollutants outside the roots by enhancing the cell wall structure, changing the pH, chelation, complexation, and precipitation of of heavy metals in the rhiza environment [24,25,26,27,28]. In this study, same-age seedlings of four different Eucalyptus species from Dongmen Forest Farm in Guangxi were selected as the research materials, among which there were three pure species: E. urophylla, E. tereticornis and E. grandis. These species are widely used in cross breeding; a widely planted hybrid E. urophylla × E. grandis was also selected. By observing the occurrence and distribution of ROS and RNS species in the root tips of Eucalyptus seedlings under Al stress, we analyzed change trends of the growth and physiological indicators of Eucalyptus seedling roots under Al stress, and attempted to answer the following questions: (1) what indicators can be used to reflect the Al sensitivity of Eucalyptus species?; (2) how high is Al tolerance of a hybrid species relative to its parent species (pure species)?; and is Al tolerance ability hereditary?

Materials and methods

Treatments

Seedlings of four different Eucalyptus species from Dongmen Forest Farm in Guangxi Province were selected, namely E. urophylla, E. tereticornis, E. grandis, and E. urophylla × E. grandis. First, Eucalyptus seedlings had been cultured in the substrates (coconut chaff: rice husk: peat soil = Weight ratio 5:3:2). After three months, healthy Eucalyptus seedlings with a seedling height of 22 ± 3.0 cm and ground diameter of 3.5 ± 1.0 mm were selected and then transported to the hydroponic system from 5 August 2019 (Supplementary Figure S1). Seedlings were sterilized with 1‰ carbendazim for 30 min, washed thoroughly with deionized water and transplanted into 3-L black plastic buckets (Supplementary Figure S2). Seedlings were hydroponically cultured with modified Hoagland nutrient solution (Supplementary Table S1) for 21 days. During this period, they were ventilated continuously with an oxygen pump and the nutrient solution was changed every 3 days (Supplementary Figure S2). The pH was maintained at 5.5 for the first 7 days and adjusted to 4.0 with hydrochloric acid (HCl) thereafter. Eucalyptus seedlings (seedling height 30.5 ± 4.2 cm, ground diameter 3.9 ± 1.4 mm) with similar growth and strong hydroponic roots were selected for the experimental treatment. The experiment was divided into two parts. First, five Al treatments (including CK, stands for control) with different concentrations were established (0, 1.5, 3.0, 4.5, and 6.0 mM, respectively). After 24 h, by measuring the relative elongation and activity of seedling roots, the optimal Al treatment concentration was determined to distinguish Eucalyptus seedlings in terms of Al tolerance (a 4.5 mM Al concentration treatment was finally selected in this experiment). In the subsequent experiment, 0 (CK) and 4.5 mM Al concentrations were established, and the malondialdehyde (MDA) content, Evans Blue uptake, O2− content, H2O2 content, antioxidant enzyme activity and osmotic regulatory substances in Eucalyptus seedling roots were determined after 24 h with and without 4.5 mM Al stress. All treatments were set up with three replicates, one pot per replicate, and eight Eucalyptus seedlings were hydroponically cultured in each pot (Supplementary Figure S2).

The experiment was conducted in the nursery (22◦ 50′ 28.41" N, 108◦ 17′ 9.00" E) of the College of Forestry of Guangxi University (Nanning City, China). The area has a subtropical monsoon climate zone, Summer is long, winter is short, the average annual temperature is 21.6 ℃, the average annual rainfall is 1304.2 mm, and the average relative humidity is 79%, the hydrothermal conditions were suitable for the growth of Eucalyptus.

Index determination method

Determination of the root relative elongation

The hydroponic roots of Eucalyptus seedlings were measured with vernier calipers (Accurate to 0.01 mm) before and after treatment. Numbers of replicates are three, each plastic bucket as one replicate and there are eight seedlings inside (Supplementary Figure S2). The longest three roots of each Eucalyptus seedling were measured, the average of the data from all eight seedlings in each plastic bucket was used as the data for that replicate, and the root relative elongation was calculated according to formula (1) [29].

$$\text{root relative elongation}=\frac{L_{treat}-L_{initial\;(treat)}}{L_{control}-L_{initial\;(control)}}\times100\%$$
(1)

Ltreat refers to the root length of the treatment group after the 24 h Al treatment, Linitial (treat) refers to the root length of the treatment group before the Al treatment, Lcontrol refers to the root length of the control group after a 24 h hydroponic control, and Linitial (control) refers to the root length of the control group before the 24 h hydroponic control.

Determination of root activity

Root activity was determined by triphenyltetrazolium chloride (TTC) method, with TTC being reduced to tribenzoate (TTF) by dehydrogenase in viable cells [30]. A 0.5 g root tip was placed into the bottom of a 50 ml plastic centrifuge tube, and 5 ml of 0.4% (W/V) TTC solution and 0.05 M phosphate buffered saline (PBS, pH = 7.0) were then added (2 ml of 1 M sulfuric acid solution was added first as a zeroing control) so that the root tip was fully immersed in the solution. The culture was incubated at 37 °C for 3 h in the dark. Then, 2 ml of 1 M sulfuric acid (H2SO4) solution was added immediately to terminate the reaction. The Eucalyptus root tip was removed with tweezers, and the root tip surface solution was gently blotted dry with filter paper. Then, the root tip was placed into a mortar with a small amount of quartz sand, and 5 ml of ethyl acetate was added for grinding and extraction. The residue remaining in the mortar was cleaned with ethyl acetate three times and completely transferred to a centrifuge tube with a constant volume of 10 mL extract. The clarified red liquid was collected and the absorbance was measured with a microplate reader at a wavelength of 485 nm.

Determination of malondialdehyde (MDA) content in roots

The MDA content was determined by the thiobarbituric acid (TBA) method [31]. First, 0 − 10 mm root tips were ground into a homogenate with trichloroacetic acid (TCA) solution, boiled in a water bath, cooled to room temperature, and centrifuged at 10,000 g for 10 min. The absorbance of the supernatant was measured at 532, 600, and 450 nm. The MDA content was calculated using the absorbance coefficient ε = 155 mM−1 cm−1.

Microscopic observation of ROS distribution in Eucalyptus roots

The O2− distribution in root tips was determined by dihydroethidium (DHE) fluorescence staining [32]. The root tips of Eucalyptus seedlings were carefully cut off with a blade and mixed with 200 μl 10 mΜ DHE (dissolved in 10 mM Tris–HCl buffer, pH 7.4) in a 96-well culture plate. After incubation at 37 °C for 30 min in the dark, the tips were washed three times with 10 mM Tris–HCl buffer (pH = 7.4), and finally observed and photographed with a Nikon E600 fluorescence microscope with a Nikon U-2A filter block (380–420 nm excitation filter, 430 nm dichroic mirror, 450 nm barrier filter).

Hydrogen peroxide can react with 3,3-diaminobenzidian (DAB) to produce brown substances [33]. The DAB staining solution (1 mg/ml) was dissolved in 50 mM Tris–HCl (pH = 3.8). Eucalyptus root tips were washed and placed into DAB staining solution, incubated and stained at 25 °C for 4 h, rinsed three times with 50 mM Tris–HCl (pH = 3.8), and photographed with a Nikon E100 light microscope.

Microscopic observation of root staining using Schiff’s reagent

Schiff reagent reacts with aldehydes in plant or animal cells to produce purplish red to purplish blue substances, and can therefore be used to detect MDA in Eucalyptus root tips. The 0—10 mm root tips were cut and stained with Schiff reagent for 20 min. The stained root tips were rinsed with 0.5% (W/V) potassium sulfite solution dissolved in 0.05 M HCl. The stained area was observed under a light microscope (Nikon E100) and photographed [34].

Microscopic observation of root uptake of Evans orchid

The integrity of the cell membrane was determined by Evans Blue staining; the larger the absorption amount of Evans Blue the deeper the staining, the more severe the damage to the cell membrane [35]. The 0 − 10 mm portion of the root tip was cut and stained in Evans Blue at a concentration of 0.25% (w/v) for 10 min. Then, the root tip was rinsed three times with deionized water, and staining was observed under a microscope (Nikon E100) and photographed [36].

Microscopic observation of the distribution of RNS in Eucalyptus root tips

The sites of nitric oxide (NO) occurrence and distribution in Eucalyptus root tips were detected by diaminofluorescein-FM diacetate (DAF-FM DA), which is a fluorescent probe for detecting low NO concentrations [37]. The root tips of Eucalyptus trees were cut off from 0 − 10 mm with a clean blade and placed into 96-well culture plates. Then, 250 μl of 15 μM DAF-FM DA (pH = 7.4, dissolved in 20 mM HEPES) was injected into the plates. After 30 min of culture at room temperature in the dark, Eucalyptus roots were washed with 20 mM HEPES (pH = 7.4) and examined with a Nikon E600 fluorescence microscope with a Nikon B-2A filter block (450–490 nm excitation filter, 505 nm dichroic mirror, 520 nm barrier filter).

Fluorescence microscopy examination of root ONOO− was carried out with aminophenyl fluorescein (APF) fluorescent probes [38]. The 0 − 10 mm parts of Eucalyptus root tips were cut off, rinsed with water, and placed in 96-well culture plates. Then, 250 μl of 10 μM APF (dissolved in 10 mM Tris–HCl, pH = 7.4) was added to completely immerse the roots, which were incubated for 60 min under dark conditions. Then, they were washed with 10 mM Tris–HCl (pH = 7.4), and finally observed and photographed with a Nikon E600 fluorescence microscope (excitation, 495 nm; emission, 515 nm).

Determination of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in Eucalyptus roots

NADPH oxidase exists specifically in the cytoplasmic membrane and must be extracted from the plant root cell membrane. Referring to the method of Zhang et al. [39], 0 − 10 mm root tips were cut from Eucalyptus seedlings with a single blade. Then, 5 ml of the extract (containing 0.5% (W/V) polyvinyl pyrrolidone (PVP), 10% (W/V) glycerol, 5 mM ethylenediamine tetraacetic acid (EDTA), 250 mM sucrose, 1 mM dithiothreitol (DTT), 1 mM phenylmethylsulfonyl fluoride (PMSF), 15 mM β-mercaptoethanol, and 25 mM Tris-mes (pH = 7.6)) were added to a precooled mortar. A small amount of quartz sand was also added to ensure that it was fully ground to homogeneous state in an ice bath environment, and it was then filtered through a double-layer gauze, and centrifuged at 13,000 g for 20 min at 4 °C. The supernatant was centrifuged at 80,000 g for 50 min at 4 °C. All of the supernatant was discarded and the precipitate was completely dissolved in 2 ml buffer containing 5 mM Tris-MES (pH = 6.5), 1 mM DTT, and 1 mM PMSF. The resulting solution was the cell membrane solution.

The NADPH oxidase activity was measured as the relative rate of O2− production by NADPH oxidase. To start the reaction, 100 μl cell membrane solution was added to 1 ml of reaction solution containing 0.5 mM sodium XTT, 50 mM Tris–HCl (pH = 7.5) and 0.1 mM NADPH, and the rate of XTT reduction was continuously measured at 470 nm absorbance (ε = 21.6 mM−1 cm−1).

Determination of Eucalyptus root antioxidant enzyme activity

A 0.5 g portion of fresh Eucalyptus seedling root tips (0 − 10 mm) was ground in liquid nitrogen to extract crude protein from the root tips in 2 mL 50 mM PBS (pH 7.0) containing 1 mM EDTA and 1% (W/V) PVP. The extract was centrifuged at 15,000 g for 20 min at 4 °C, and the supernatant was used for the determination of the following enzyme activities [40].

The activity of superoxide dismutase (SOD) was determined based on the degree intensity of inhibition of the photochemical reduction of nitro blue tetrazolium chloride (NBT). The 3 ml reaction system consisted of 50 mM PBS (pH 7.8), 1% (W/N) EDTA, 130 mM methionine, 750 μM NBT, and 100 μM riboflavin. Finally, 100 μl crude enzyme extract was added and exposed to light (4,000 LX intensity) for 20 min. We did not use NBT, enzyme extract or dark treatments as controls. The absorbance was measured at 560 nm and one unit (U) of SOD activity was defined as the amount of enzyme required for NBT to be photoreduced by 50%.

Catalase (CAT) activity was determined by measuring the decomposition rate of H2O2 in the reaction system after the addition of crude enzyme extract. The reaction system consisted of 3 mL of 100 mM PBS(Ph 7.0),1 μM EDTA, and 20 mM H2O2, and 100 μl of enzyme extract was added to start the reaction.

S-nitrosoglutathione reductase (GSNOR) was obtained by measuring NADH oxidation [41]. A 3 mL colorimetric reaction system containing 20 mM Tris–HCl (pH = 8.0), 0.2 mM NADH, 0.5 mM EDTA, and S-nitrosoglutathione (GSNO final concentration 400 μM) was added to start the reaction, and the reaction was measured at 340 nm (ε = 6.22 mM−1 cm−1).

Ascorbate peroxidase (APX) activity was determined by measuring the oxidation of ascorbate at 290 nm. The 3 ml reaction system contained 1.7 ml 50 mM PBS (pH = 7.0), 0.1 ml 30 mM ascorbic acid (AsA), and 1 ml 0.9 mM H2O2; 0.2 ml enzyme extract was added to start the reaction. Changes in optical density values (ε = 2.8 mM−1 cm−1) were continuously measured at 290 nm [40].

Determination of osmotic regulatory substances in Eucalyptus roots

The soluble protein content was determined using Coomassie brilliant blue G-250 staining [42]. A 0.5 g portion of fresh Eucalyptus seedling root tips (0 − 10 mm) was weighed, cut into pieces and placed in a pre-cooled mortar. Then 5 mL of pre-cooled 0.1 M PBS (pH = 7.0) and a small amount of quartz sand were added, fully ground into homogenates in an ice bath environment, and centrifuged at 4,000 g for 10 min at 4 °C. Next, 0.1 ml of the extract was absorbed, and 5 ml of 100 mg/L Coomassie brilliant blue G-250 solution (dissolved in 50 ml 90% ethanol and 100 ml 85% phosphoric acid, with the volume was fixed in 1,000 ml of distilled water) was added; the absorbance of the solution was then measured at 595 nm.

The soluble sugar content in plants was determined by the anthrone colorimetry method [43]. A 0.5 g portion of fresh Eucalyptus root tips (0 − 10 mm) was weighed, cut into pieces, and placed into a mortar. A small amount of quartz sand and distilled water were added to enable the root tips to be ground into a homogenate, which was then transferred to a 20-ml glass test tube. The mortar was washed with distilled water, which was transferred to a test tube together with the extract; the total volume was 10 ml. The extract was boiled in a water bath for 10 min, cooled, and filtered with filter paper and funnel; the filtered extract was transferred to a volumetric flask of 100 mL. The volume was fixed with distilled water and the flask was shaken; then, 1 ml of the liquid was absorbed into a plastic centrifuge tube with a lid, and 1 ml of distilled water and 0.5 ml of 2% (W/V) anthrone reagent (dissolved in ethyl acetate) were added. Then, 5 ml of concentrated H2SO4 was added carefully and slowly, and the tube was gently shaken, placed in a boiling water bath for 10 min, and cooled to room temperature (1 ml of distilled water was used to replace the extract for reaction). Finally the absorbance was determined at 620 nm.

The proline content in plants is one of the most important indicators of the tolerance to stress. Proline will react with acid ninhydrin to produce red substances and is therefore used to detect the proline content in plants [44]. A 0.5 g portion of fresh Eucalyptus hydroponic root tips (0 − 10 mm) was cut into pieces with clean scissors and placed into a mortar. A small amount of quartz sand and 5 ml of 80% ethanol were added to fully grind the tips into a homogenate, which was then transferred to a glass test tube. The mortar residue was washed three times with 5 mL of 80% ethanol and transferred to a test tube together with the extract; the volume was 10 ml (80% ethanol). The solution was mixed thoroughly and extracted in an 80 °C water bath for 30 min. Then, 2 ml of the extract was absorbed into a 10 mL centrifuge tube, and 2 ml of 80% ethanol was absorbed into another centrifuge tube as a control. Then, 2 ml glacial acetic acid or 2 ml 2.5% ninhydrin reagent was added to each centrifuge tube, and the reaction solution was further boiled in the water bath for 15 min. After cooling, the absorbance in the reaction solution was detected at 520 nm.

Data processing

A two-factor analysis of variance (ANOVA) was used to detect significant differences in root relative elongation and root activity among species (E. urophylla, E. tereticornis, E. grandis, and E. urophylla × E. grandis) and the Al levels (0, 1.5, 3, 4.5, 6 mM), and we compared the interspecies difference within each dosage or/ and dose interval difference for each species by Multiple mean comparison as Tukey’s HSD test (Fig. 1). According to the difference of the response of root relative elongation and root activity to different Al concentrations among species, an Al concentration that can distinguish four Eucalyptus species was selected for the next test. Then, another two-factor ANOVA was used to detect significant differences in physiological indicators among species and the Al stress (0, 4.5 mM), and we compared the interspecies difference within each dosage or/ and dose interval difference for each species by Multiple mean comparison as Tukey’s HSD test (Fig. 6). All values are means of three replicates (n = 3, ± SD). SPSS 25.0 software (IBM Corp.) was used for the analysis. To assess the interspecific differences in all physiological indicators, principal component analysis (PCA) was used to reduce the dimensionality of the response variables. PCA was conducted using R-4.0.3 software (R Development Core Team) to investigate tolerance based on a set of traits (Fig. 9 and Supplementary Table S2 and S3). SigmaPlot (Systat Software Inc.) 12.0 and R 4.03 were used to produce graphs (Figs. 1, 6 and 9) [45].

Fig. 1
figure 1

Effects of different concentrations of Al on root relative elongation and root activity of four Eucalyptus species seedlings. * and ** indicate statistical significance among species at P < 0.05 and P < 0.01, respectively. Based on Multiple mean comparison such as Tukey’s HSD test, the different lowercase letters indicate that there are statistical significances among species at P < 0.05, and the different capital letters indicate that there are statistical significances among Al concentrations at P < 0.05. All values are means of three replicates (n = 3, ± SD)

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Results

Effects of Al stress on the growth and activity of Eucalyptus seedling roots

With an increase in Al concentration, the root relative elongation of the four Eucalyptus species decreased significantly (Fig. 1). Under 4.5 and 6 mM Al stress, the root relative elongation was significantly different among the four species. In general, the root relative elongation was highest for E. urophylla × E. grandis roots, followed (in order) by those of E. urophylla, E. grandis, and E. tereticornis. With an increase in Al concentration, the root activity of the four Eucalyptus species decreased significantly. The root activity of E. urophylla × E. grandis was highest, followed (in order) by E. urophylla, E. tereticornis, and E. grandis. Under 4.5 mM Al concentration stress, multiple comparative analysis showed that the root relative elongation of E. urophylla × E. grandis was significantly higher than that of E. tereticornis, and the root activity of E. urophylla × E. grandis and E. urophylla was significantly higher than that of E. tereticornis and E. grandis (Fig. 1). Because there were significant differences in root relative elongation and root activity among the four Eucalyptus species under 4.5 mM Al stress, the 4.5 mM Al concentration was selected for subsequent stress experiments.

Microscopic observation of superoxide anion accumulation in Eucalyptus root tips under Al stress

Without Al stress, Species showed obvious (Eucalyptus grandis), slight (E. tereticornis and E. urophylla) and did not show fluorescence staining (E. urophylla × E. grandis) (Fig. 2). After 24 h of Al stress, the four Eucalyptus species showed different degrees of fluorescence staining (Fig. 2). The staining of E. urophylla × E. grandis and E. urophylla was mild, while the staining of E. tereticornis and E. grandis was severe. In general, the staining sites were all in the root cap, indicating that the O2− produced by the four Eucalyptus species under Al stress was mainly concentrated in the root cap.

Fig. 2
figure 2

Distribution of superoxide anions in root tips of four Eucalyptus species seedlings a, c, e and g represent the distribution of superoxide anion in the root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis seedlings without Al stress, respectively. b, d, f and h represent the distribution of superoxide anion in root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis after Al stress, respectively. Arrows indicate the stained sites

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Microscopic observation of H2O2 accumulation in Eucalyptus root tips under Al stress

Without Al treatment, the roots of the four Eucalyptus species were slightly stained, indicating that a certain amount of H2O2 had been produced and accumulated in the roots in the hydroponic environment (Fig. 3). There was no significant difference in staining of the root tips of the four Eucalyptus species without the Al treatment (Fig. 3). After 24 h of Al stress, the root tips of the four Eucalyptus species exhibited deeper staining than those of the control group. The degree of staining was highest in E. tereticornis, in which the entire root tip was stained, indicating that large amounts of H2O2 had accumulated there. The roots of E. grandis also showed obvious staining after Al stress, with the stained parts mainly being concentrated in the meristem, elongation, and mature areas. The degree of staining of E. urophylla and E. urophylla × E. grandis under Al stress was less than that of the other two species, and staining was mainly concentrated in the root meristem and maturation areas.

Fig. 3
figure 3

Location and distribution of hydrogen peroxide in root tips of four Eucalyptus species seedlings without and with Al treatment a, c, e and g represent the distribution of hydrogen peroxide in the root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis seedlings without Al stress, respectively. b, d, f and h represent the distribution of hydrogen peroxide in root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis after Al stress, respectively

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Microscopic observation of Schiff reagent uptake by Eucalyptus root tips under Al stress

According to Fig. 4, there was no significant difference in the staining of E. urophylla root tips after Al stress compared with CK (without Al stress). After the Al stress treatment, the staining of the root tip of E. urophylla × E. grandis was slightly deeper than that of CK, and was mainly concentrated in the root meristem area. The staining of the root tip of E. grandis and E. tereticornis was significantly deeper after Al stress than in plants without Al stress, and the root cap, meristem area and mature area of the root tip were all severely stained.

Fig. 4
figure 4

Distribution of schiff’s reagent uptake in root tips of four Eucalyptus species seedlings without and with Al treatment a, c, e and g represent the distribution of schiff’s reagent uptake in the root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis seedlings without Al stress, respectively. b, d, f and h represent the distribution of schiff’s reagent uptake in root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis after Al stress, respectively

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Microscopic observation on the uptake of Evans blue in Eucalyptus root tips under Al stress

As shown in Fig. 5, the root tips of the four Eucalyptus species were relatively lightly stained without Al stress. After a 4.5 mM Al treatment for 24 h, root tip staining of all four Eucalyptus species seedlings had deepened. The entire apical area of E. tereticornis and E. grandis was severely stained, with E. grandis having the deepest and most widely distributed stained area. A small number of unstained areas were observed in the root cap of E. tereticornis, and a few intact viable cells remained. Compared with the control group, the staining of E. urophylla under Al stress was also significantly deeper, with severe staining of the whole root tip. The results indicated damage to all root cells in E. urophylla. Only the root cap and mature zone of E. urophylla × E. grandis seedlings showed severe staining; there was no obvious staining in other parts of the root tip, indicating that most of the cells in the root elongation zone could maintain their original activity under 4.5 mM Al stress. In summary, the damage to the root tip cells of E. grandis and E. tereticornis under Al stress was more severe than that of E. urophylla and E. urophylla × E. grandis.

Fig. 5
figure 5

Distribution of Evans blue uptake in root tips of four Eucalyptus seedlings without and with Al treatment a, c, e and g represent the distribution of Evans blue uptake in the root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis seedlings without Al stress, respectively. b, d, f and h represent the distribution of Evans blue uptake in root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis after Al stress, respectively

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Changes in physiological indicators of Eucalyptus root tips under Al stress

In general, the physiological indicators displayed an upward trend after 24 h of Al stress (Fig. 6). Although there was no statistically significant difference in whether Al was added or not, the NADPH oxidase activity of E. tereticornis was 62.46% higher after Al stress than in plants without Al stress, and the same trend was observed in E. grandis (33.04%) (Fig. 6a). For E. urophylla and E. urophylla × E. grandis, NADPH oxidase activity after Al stress was not significantly different from in plants without Al stress. The SOD activity and soluble protein content in the seedling root tips of all four Eucalyptus species were significantly increased after Al stress compared to plants without Al stress, except there was not significantly difference between Al stress or without Al stress for soluble protein of E. urophylla × E. grandis (Fig. 6b and i). Although significantly higher activities were observed only in particular species not in all the four species in a statistical sense (CAT in E. urophylla × E. grandis, and APX in E. grandis), the CAT, POD, and APX activities in the root tips of the four Eucalyptus species seedlings after Al stress were higher than in plants without Al stress on average (Fig. 6c, d and e). It is worth noting that the relative increments of POD and APX of E. grandis and E. tereticornis after Al stress were higher than that of E. urophylla and E. urophylla × E. grandis, while the opposite is true for CAT. Although there was no significant difference between species, under Al stress the CAT activity of E. urophylla and E. urophylla × E. grandis was higher than that of E. grandis and E. tereticornis on average, while under Al stress the POD activity of E. urophylla and E. urophylla × E. grandis was lower than that of E. grandis and E. tereticornis on average. Multiple comparative analyses showed that the APX activity of E. urophylla and E. urophylla × E. grandis was higher than that of E. grandis and E. tereticornis (although there was no statistically significant difference among E. urophylla, and E. grandis, and E. tereticornis under Al stress, the average APX activity of E. urophylla was still higher than that of E. grandis and E. tereticornis) (Fig. 6c, d and e). The relative increments of AsA contents of E. grandis, E. urophylla and E. urophylla × E. grandis after Al stress were higher than E. tereticornis on average, although significantly higher AsA contents were observed only in E. urophylla and E. grandis (Fig. 6f). Multiple comparative analysis showed that the AsA content of E. urophylla and E. urophylla × E. grandis was significantly higher than that of E. tereticornis under Al stress. The AsA content of E. urophylla and E. urophylla × E. grandis was slightly higher than that of E. grandis under Al stress, although there was no significant difference among three species. Under Al stress, the relative increments of MDA, proline, soluble protein and soluble sugar contents of E. grandis and E. tereticornis after Al stress were higher than that of E. urophylla and E. urophylla × E. grandis on average (Fig. 6g, h, i and j). Under Al stress, the MDA, proline, soluble protein and soluble sugar contents of E. grandis and E. tereticornis were significantly higher than that of E. urophylla and E. urophylla × E. grandis, except there was not significantly difference among E. urophylla, E. tereticornis and E. urophylla × E. grandis for MDA content and not significantly difference between E. urophylla and E. grandis for soluble protein. The proline contents in the root tips of E. grandis and E. tereticornis under Al stress were significantly increased compared to plants without Al treatment, while that of E. urophylla × E. grandis and E. urophylla with and without Al stress were not significantly different (Fig. 6h). The GSNOR content in the root tips of E. urophylla and E. urophylla × E. grandis under Al stress was significantly higher than in plants without Al stress, while for that of E. tereticornis and E. grandis the GSNOR content was not significantly different between plants with and without Al stress (Fig. 6k).

Fig. 6
figure 6

Changes of physiological indexes in root tips of four Eucalyptus seedlings without and with Al treatment for 24 h. The percentage represents the relative increment of physiological indexes under Al stress compared with those without Al stress. Based on Multiple mean comparison as Tukey’s HSD test, * and ** indicate statistical significance between plant physiological indexs with and without Al stress at P < 0.05 and P < 0.01, and the different capital letters indicate that there are statistical significances among species without Al stress at P < 0.05, and the different lowercase letters indicate that there are statistical significances among species with Al stress at P < 0.05. All values are means of three replicates (n = 3, ± SD). EU, E. urophylla; ET, E. tereticornis; EG, E. grandis; EU × EG, E. urophylla × E. grandis

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Microscopic observation of NO content in Eucalyptus root tips under Al stress

According to Fig. 7, without Al stress only the root cap of E. grandis showed slight staining, while no staining was observed in the other three Eucalyptus species. The seedling root tips of all four species showed obvious staining after a 24 h Al treatment, but the degree and location of staining differed. The root staining of E. urophylla was concentrated from the root cap to the elongation zone, while in E. tereticornis it mainly occurred from the apical meristem to the mature area, and the root cap was only slightly stained. The root staining of E. grandis occurred in the whole root tip, and that of E. urophylla × E. grandis occurred from the apical meristematic zone to the mature zone. In general, the degree of staining of E. urophylla after Al stress was the lowest among the four species.

Fig. 7
figure 7

Distribution of nitric oxide in root tips of four Eucalyptus seedlings without and with Al treatment. a, c, e and g represent the distribution of nitric oxide in the root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis seedlings without Al stress, respectively. b, d, f and h represent the distribution of nitric oxide in root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis after Al stress, respectively. Arrows indicate the stained sites

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Microscopic observation of ONOO− content in Eucalyptus root tips under Al stress

As shown in Fig. 8, no obvious staining occurred in the roots of E. urophylla and E. grandis without Al stress, while there was slight staining of the roots of the other two Eucalyptus species. After the Al treatment, the whole root tip of E. tereticornis displayed obvious fluorescent staining. After the Al treatment, the root caps of E. urophylla and E. grandis exhibited fluorescent staining, indicating that ONOO− mainly accumulated in the root cap area. Moreover, the degree of staining of E. grandis was greater than that of E. urophylla. There was no significant staining in the root tip of E. urophylla × E. grandis with Al stress.

Fig. 8
figure 8

Production sites and contents of ONOO− in root tips of four Eucalyptus seedlings without and with Al treatment. a, c, e and g represent the production sites and contents of ONOO− in the root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis seedlings without Al stress, respectively. b, d, f and h represent the production sites and contents of ONOO− in root tips of Eucalyptus urophylla, E. tereticornis, E. grandis and E. urophylla × E. grandis after Al stress, respectively. Arrows indicate the stained sites

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PCA

Principal components (PCs) with values > 1 were retained, and the first three PCs accounted for 80.72% of the variance in the 13 original variables. PC1, which accounted for 54.83% of the variance, was mainly affected by APX, soluble sugar, MDA, soluble protein, proline, the root relative elongation of roots, and root activity. PC2, which accounted for 15.87% of the variance, was mainly affected by POD and SOD. PC3, which accounted for 10.02% of the variance, was mainly affected by ASA (Supplementary Table S2 and Table S3). The loadings of the 13 physiological indexes on the three PCs represented the three main components of the Al tolerance of Eucalyptus seedlings. PC1 represented root morphology and the osmotic regulation mechanism, PC2 represented antioxidant enzymatic activity, and PC3 represented non-enzymatic antioxidant activity.

According to Fig. 9, PC1 has a strong ability to distinguish the four Eucalyptus species, which could be clearly divided into two types: Eucalyptus urophylla and E. urophylla × E. grandis, and E. tereticornis and E. grandis. The two types were distributed to the left and right sides of the axis. According to Fig. 9 and Supplementary Table S3, the suppressions of root relative elongation and root activity, and the accumulations of soluble sugar, soluble protein and proline were good indicators of Al sensitivity of Eucalyptus (composition matrix ≥ 0.9; Supplementary Table S3). These results indicated that the root morphology and osmotic regulatory substance content of Eucalyptus were sensitive to Al stress. The differences between PC2 and PC3 were not significant for the four Eucalyptus species.

Fig. 9
figure 9

Principal component analysis of the thirteen physiological variables for the four species. A first principal component (PC1) vs. second PC (PC2); B PC1 vs. third PC (PC3). EU, E. urophylla; ET, E. tereticornis; EG, E. grandis; EUG, E. urophylla × E. grandis

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Multiple comparisons of the PC values showed that, for PC1, E. tereticornis and E. grandis were ranked significantly higher than E. urophylla and E. urophylla × E. grandis. For PC2 and PC3, there were no significant differences among the four Eucalyptus species. Finally, E. tereticornis and E. grandis were ranked significantly higher for the integrated PCs than E. urophylla and E. urophylla × E. grandis (Supplementary Figure S3).

Discussion

Differential analysis of the root responses of different Eucalyptus species to Al stress

Inhibition of root elongation is the most typical feature of plants in the early stage of Al toxicity stress [46]. In this study, the relative elongation and activity of the roots of four Eucalyptus species showed a significant downward trend after Al stress. Different Eucalyptus species have different root growth responses to Al stress. In this study, we found that the relative elongation and activity of the roots of the four Eucalyptus species decreased by different degrees after 4.5 mM Al stress for 24 h, and there were significant differences among species (Fig. 1). The F of 4.5 mM Al treatment was higher than the F of 3.0 mM and 6.0 mM, which also indicated that the difference of root relative elongation and root activity among the four species under 4.5 mM Al stress was greater than 3.0 and 6.0 mM (Fig. 1). Therefore, we selected the 4.5 mM Al stress test for subsequent analyses of the differences in Al tolerance between Eucalyptus species.

Stress often disturbs the redox state in plants, resulting in excessive accumulation of ROS and oxidative damage. Additionally, stress can induce the production of NO and other RNS derived from plants, which will also disturb the redox homeostasis in plant cells [14, 15, 47]. The root tip is considered to be the original site of plant Al toxicity, and is the main site of accumulation of callose, which is a sensitive marker of Al toxicity [48, 49]. In this study, Al stress induced significant ROS and RNS accumulation in Eucalyptus roots (Figs. 2, 3, 7 and 8), and the staining sites were largely concentrated in the root cap, meristem and elongation zone, and mature areas. The staining of E. tereticornis and E. grandis was significantly deeper than that of E. urophylla and E. urophylla × E. grandis, indicating that more ROS and RNS accumulated in the roots of E. tereticornis and E. grandis compared to the other two Eucalyptus species. This result showed that the changes of root tip redox status and antioxidant system of different Eucalyptus species were due to differences in Al tolerance. Aluminum stress led to a 62.46% increase in the activity of NADPH oxidase in E. tereticornis compared to the NO Al treatment, which was higher than that in the other three Eucalyptus species. Conversion of O2− produced by plasma membrane NADPH oxidase into H2O2 catalyzed by SOD is an important way to induce oxidative stress under adverse conditions [50]. In this study, the SOD activity of the root tips of the four Eucalyptus species after Al stress was significantly higher than in plants without stress. Under Al stress the accumulation of O2− and H2O2 in the root tips of E. tereticornis and E. grandis was significantly higher than in plants E. urophylla and E. urophylla × E. grandis (Figs. 2 and 3). Peroxidase is an antioxidant enzyme with dual functions. It can generate H2O2 from NADH as an electron donor, and also directly participates in the scavenging of H2O2 [51, 52]. In this study, the relative increments of POD of E. grandis and E. tereticornis under Al stress were higher than that of E. urophylla and E. urophylla × E. grandis, and the POD activity of E. urophylla and E. urophylla × E. grandis was lower than that of E. grandis and E. tereticornis after Al stress; this indicates that the higher POD activity seen under Al stress may contribute to the higher H2O2 content in the root tips of E. tereticornis and E. grandis. CAT and APX are involved in the scavenging of H2O2 and maintenance of intracellular redox homeostasis. APX scavenges H2O2 with AsA as a substrate, while CAT can directly scavenge H2O2 [50, 53]. AsA is an important non-enzymatic antioxidant that is ubiquitous in most plants. In addition to participating in the H2O2 scavenging process as a substrate catalyzed by APX, AsA can also react directly with H2O2 to scavenge H2O2 [50, 54]. In this study, the lower CAT activity seen under Al stress may have led to a lower H2O2 removal efficiency from root tips of E. tereticornis and E. grandis than the other two species. The APX activity and AsA content in the root tips of E. urophylla and E. urophylla × E. grandis were higher than those of E. tereticornis and E. grandis with Al stress, which indicated that E. urophylla and E. urophylla × E. grandis root tips had higher H2O2 scavenging efficiency. These findings may explain the high H2O2 content of E. tereticornis and E. grandis.

Various abiotic stresses, such as salinity, mechanical damage, UV irradiation, ozone, and heavy metal toxicity, can result in the production of NO and other RNS in plants [15, 41, 55, 56]. An appropriate amount of NO can function as a signaling molecule and improve the tolerance of plants to adversity; however, excessive NO accumulation can interfere with the redox state in plant cells and cause nitrification stress [15, 16]. This study showed that the NO (Fig. 7) and ONOO− (Fig. 8) contents in the tips of E. tereticornis and E. grandis were significantly higher than in E. urophylla and E. urophylla × E. grandis after Al stress. Aluminum stress significantly increased GSNOR activity in the root tips of E. urophylla and E. urophylla × E. grandis, but had no significant effect in E. tereticornis and E. grandis (Fig. 6k). It has been reported that plant GSNOR can reduce the levels of NO and s-nitrosothiols (SNOs) in plants by degrading its GSNO substrate [57]. This may be the main reason why the NO and ONOO− contents in root tips of E. tereticornis and E. grandis were significantly higher than those of E. urophylla and E. urophylla × E. grandis (Figs. 7 and 8).

In general, under Al stress, the effects of oxidative and nitrification stress on E. tereticornis and E. grandis were greater than those on E. urophylla and E. urophylla × E. grandis. The proline, soluble sugar, and soluble protein contents of E. tereticornis and E. grandis under Al stress were higher than that of E. urophylla and E. urophylla × E. grandis (Figs. 6h, i and j). Moreover, under Al stress, the amount of membrane lipid peroxidation product (MDA) was higher in E. tereticornis and E. grandis than in E. urophylla and E. urophylla × E. grandis (Fig. 6g), which indicated that the Al tolerance of E. tereticornis and E. grandis was weaker than that of E. urophylla and E. urophylla × E. grandi. Aluminum stress induced differences in antioxidant enzyme activity in root tips among the different Eucalyptus species, resulting in different ROS and RNS contents. Although E. grandis and E. tereticornis tried to maintain the function and integrity of the membrane by synthesizing more osmotic regulatory substances than E. urophylla and E. urophylla × E. grandis, the membranes of E. grandis and E. tereticornis still suffered great damage, and the MDA content was higher than that of E. urophylla and E. urophylla × E. grandis. Ultimately, this led to differences in the degree of membrane lipid peroxidation, which may be an important factor driver of the differences in Al tolerance among Eucalyptus species.

Main indexes characterizing species differences in Al tolerance

The results showed that that root relative elongation, root activity, soluble sugar, soluble protein, and proline are important factors that characterize the Al tolerance of Eucalyptus (component matrix ≥ 0.9; Supplementary Table S3). Root length is one of the most sensitive morphological indicators, and inhibition of root elongation can be observed in many plants within hours or even tens of minutes after micromolar Al treatment [58,59,60]. Aluminum stress may impede cell differentiation and increase cell wall stiffness, thereby limiting root elongation; this leads to poor root hair development, and ultimately affects root uptake and the utilization of water and nutrients [61,62,63]. To protect themselves against stress, plants can also biosynthesize soluble compounds such as carbohydrates (including soluble sugars and soluble proteins), proline and betaine to regulate cell osmosis, maintain membrane integrity and function, and stabilize enzymatic activities [64, 65]. As an organic acid, proline can also activate soil nutrient elements and promote plant absorption of mineral nutrients under adversity [21, 66, 67]. As can be seen from Fig. 9, root relative elongation and root activity of E. urophylla and E. urophylla × E. grandis were higher than those of E. grandis and E. tereticornis. However, the contents of soluble sugar, soluble protein and proline in the roots of E. urophylla and E. urophylla × E. grandis were lower than those of E. grandis and E. tereticornis. This result showed that the changes of root growth, redox status and antioxidant system, osmosis regulation, and peroxidation of membrane lipid of different Eucalyptus species were due to differences in Al tolerance. These indicators can be used as the key factors to evaluate the Al sensitivity of Eucalyptus species.

Factors underlying species differences in Al tolerance

According to the PCA results for the root indexes, the four Eucalyptus species could be divided into two categories (E. grandis and E. tereticornis, and E. urophylla and E. urophylla × E. grandis) (Figs. 9 and Supplementary Figure S3). This agrees with the results of previous studies that used physiological indexes of Eucalyptus leaves [68]. From a phylogenetic perspective, the three purebred Eucalypts had different native sites [69]. The native land of E. urophylla is located in the volcanic islands of eastern Indonesia, where the soil has high Al content [69,70,71]. Eucalyptus grandis is native to eastern Australia and E. tereticornis is distributed from Papua New Guinea to southern Australia [72, 73]. The Soil Al content in these areas is lower than in the volcanic islands of eastern Indonesia. Thus, through long-term selection in Al-rich environments, E. urophylla has developed adaptations to relatively high Al concentrations. When leaves were used as test materials, we found that the Al tolerance of E. urophylla × E. grandis and E. tereticornis was intermediate between that of E. urophylla and E. grandis [68], while the Al tolerance of E. urophylla × E. grandis was greater than that of E. urophylla and E. grandis in this study. The Al tolerance of E. tereticornis was lowest when roots were used as test materials in this study. This may be due to tissue-specific differences between different organs or tissues within individuals. In this study, E. urophylla × E. grandis had higher Al tolerance than its parents, which may be due to heterosis [74, 75]. The hybridization of parents with different genotypes may result in dominant genes, complementarity, and a rich allelic diversity [76]. The results obtained using both root and leaf materials indicated that E. urophylla × E. grandis shared similar characteristics to its parent species (E. urophylla), further suggesting that its tolerance to Al stress is heritable, regulated by a few genes, and largely inherited by hybrid species. Many countries have conducted studies on the breeding and planting of improved Eucalyptus hybrid varieties, and batches of improved varieties with high yield, high tolerance, and high adaptability [77, 78] have been selected. Additionally, genetic control of Al tolerance has been reported for some crops, indicating that the breeding of Al-tolerance genotypes in Eucalyptus is feasible [79,80,81,82]. Although the hybrid was found to have strong Al tolerance similar to the female parent in this study, the male parent (E. grandis) had low Al tolerance. Therefore, Al tolerance may be maternally inherited, and the major cause of maternal inheritance during germ cell and sperm cell development may be the degradation or substantial reduction of paternal mitochondrial DNA [83]. A reciprocal test is needed to further validate the genetic characteristics of Al tolerance in Eucalyptus species.

Conclusion

Under Al stress, E. grandis and E. tereticornis had relatively higher POD activity and lower CAT and APX activities and AsA content than E. urophylla and E. urophylla × E. grandis. The higher production efficiency and lower removal efficiency of H2O2 may be the main reasons for the greater accumulation of ROS in E. grandis and E. tereticornis. Additionally, Al stress significantly increased GSNOR activity in the root tips of E. urophylla and E. urophylla × E. grandis, which effectively alleviated the nitrification caused by Al stress. Compared to E. urophylla and E. urophylla × E. grandis, E. grandis and E. tereticornis roots accumulated more ROS and RNS. Although E. grandis and E. tereticornis tried to maintain the function and integrity of the membrane by synthesizing more osmotic regulatory substances than E. urophylla and E. urophylla × E. grandis, the membranes of E. grandis and E. tereticornis still suffered great damage, and the MDA content was higher than that of E. urophylla and E. urophylla × E. grandis. In general, E. urophylla and E. urophylla × E. grandis were more resistant to Al stress than E. grandis and E. tereticornis. This study confirmed that differences in Al toxicity tolerance are related to long-term selection in the original habitat of the species, and that Al tolerance is hereditary. Eucalyptus urophylla had stronger Al tolerance than its parents, which was indicative of heterosis. These results provide theoretical support for the breeding of tree species in areas with acidic soil.

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Author notes

  1. Zilong Ouyang and Bing Liu contributed equally to this work.

Authors and Affiliations

  1. Guangxi Colleges and Universities Key Laboratory for Cultivation and Utilization of Subtropical Forest Plantation, Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning, 530004, China

    Zilong Ouyang, Bing Liu, Tangkan Li, Tiandao Bai & Weichao Teng

  2. Nanning Botanical Garden, Nanning, 530002, China

    Zilong Ouyang & Tangkan Li

  3. Key Laboratory of National Forestry and Grassland Administration on Cultivation of Fast-Growing Timber in Central South China, College of Forestry, Guangxi University, Nanning, 530004, China

    Zilong Ouyang, Tiandao Bai & Weichao Teng

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  1. Zilong Ouyang
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Contributions

Zilong Ouyang wrote the paper. Bing Liu and Tangkan Li performed the experiments and collect the data. Tiandao Bai analysed the data, and revised the paper. Weichao Teng designed and conceived the study, and revised the paper. All authors reviewed and approved the final manuscript.

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Correspondence to Weichao Teng.

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Ouyang, Z., Liu, B., Li, T. et al. Effects of aluminum on metabolism of reactive oxygen species and reactive nitrogen species in root tips of different Eucalyptus species. BMC Plant Biol 25, 55 (2025). https://doi.org/10.1186/s12870-024-06042-z

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BMC Plant Biology

ISSN: 1471-2229

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