Next Article in Journal
Residents’ Perception-Based Typology of Forest Landscape: A Case Study of Changsha, Central China
Next Article in Special Issue
Litsea Males Are Better Adapted to Pb Stress Than Females by Modulating Photosynthesis and Pb Subcellular Distribution
Previous Article in Journal
Determination of Leaf pH without Grinding the Sample: Is It Closer to the Reality?
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Forests
Volume 13
Issue 10
10.3390/f13101641
forests-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Impact of Silica Addition on Alleviating Cadmium Stress: Case Studies of Three Afforestation Tree Species Seedlings in Southern China

by
Ziyang Wang
1,†,
Shaofei Jin
2,†,
Yi Su
1,
Dongmei He
1,
Yunxiang Wang
1,
Yifei Chen
1,
Chenlei Lin
1,
Xiaoli Liao
2 and
Dexiang Zheng
1,*
1
College of Forestry, Fujian Agriculture and Forestry University, Fuzhou 350002, China
2
College of Geography and Oceanography, Minjiang University, Fuzhou 350108, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Forests 2022, 13(10), 1641; https://doi.org/10.3390/f13101641
Submission received: 25 September 2022 / Accepted: 3 October 2022 / Published: 7 October 2022
(This article belongs to the Special Issue Soil Contamination in Forest Ecosystem)
Browse Figures
Versions Notes

Abstract

:
Cadmium (Cd) stress is becoming an increasing menace for plants, inducing a series of negative effect. Silicon (Si) plays an important role in mitigating Cd stress in plants. Here, we conducted a one-year experiment with three kinds of tree species seedlings (Schima superba, Chinese sweetgum, Chinese fir) and five levels of Cd treatments (0 mg·kg−1, 6 mg kg−1, 12 mg kg−1, 24 mg kg−1, 36 mg kg−1) with or without 1 g kg−1 Si addition to investigate the mitigation effect of Si on woody plants. The results in this study showed that Cd stress triggered morphological and physiological changes, inhibiting the growth of the three kinds of tree species seedlings. Low concentrations of Cd treatment stimulated the biomass production of Schima superba and Chinese sweetgum seedlings, whereas the biomass production of Chinese fir was not stimulated by Cd treatment. The stimulatory effects were also observed in the antioxidant enzyme (SOD, POD, CAT) activities of the three kinds of seedlings. The MDA contents decreased with the rise of Cd treatments. Soil pH decreased under Cd stress. BCF values of different fractions were observed to increase with the rise of Cd treatments, except for the leaf BCF value of Chinese sweetgum. The root−to−stem TF values of all increased compared with the control, while the root-to-leaf TF values were observed to decrease. Si addition enhanced the growth of the three kinds of tree species seedlings, inducing the increase of heights, ground diameter, leaf morphological parameters, biomass production, the content of chlorophyll and the activities of antioxidant enzymes. Treatment with Si significantly decreased the Cd concentration in different fractions of the three kinds of seedlings. Soil pH increased after treatment with Si. The BCF values for Si-treated plants were all observed to be lower than the non-Si-treated ones. However, the addition Si did not affect the root-to-stem and root-to-leaf TF values in the three kinds of seedlings.

1. Introduction

Heavy metal, deriving from anthropogenic activities and the development of industry, is one of the most severe pollutions threatening the environment Nowadays, more and more heavy metals are rampantly contaminating the environment. As a nonnutritive element, cadmium (Cd) has a detrimental effect on plants [1]. Much attention has been paid to Cd pollution because of its mobility and the small concentrations of it required for toxicity. The negative effects of Cd include the decline of biomass production and soluble protein content, the disturbance of metabolism, the retardation of enzymatic activities and the excessive production of reactive oxygen species (ROS), thereby stunting plant growth [2,3,4,5]. Additionally, the presence of Cd may undermine the microorganisms in soil, which may result in a decline in soil organic matter decomposition, and thus lead to decrease in soil nutrients, while soil nutrients are generally believed to have strong effects on seed yield [6,7], the recruitment of plant communities [8,9] and some other crucial functions for plants. Therefore, it is vital to enhance the capacity of defenses against the adverse impacts induced by Cd stress in plants.
Silicon (Si), the second most abundant element in the earth’s crust, has now gained wide attention due to its benefits for plants. It is well-documented that Si protects plants against both biotic and abiotic stresses [10]. With respect to biotic stress, the mechanisms through which Silicon mitigates heavy metal toxicity are mainly composed of three actions, including the physical, biochemical and molecular processes [11]. For instance, Si can interact with principal components of plant stress singling systems, thereby inducing defenses against fungi [12]. The mitigation effect of Si has also been observed in a variety of plants under heavy metal stress [13,14]. Concerning abiotic stresses, many mechanisms has been proven to be involved in Si’s mitigating of heavy metal toxicity: decreasing the content of bioavailable heavy metal elements in soil, reducing the uptake and translocation of heavy metal elements, stimulating the activities of antioxidant enzymes and regulating the expression of genes regulating heavy metal transportation [13,15]. Guo et al. [16] demonstrated that Si mitigated Cd stress in rice plants by inhibiting the translocation and accumulation of Cd. Addition of Si was also reported to enhance the capacity of thylakoid formation [17] and to reduce the uptake of Cd and Cd translocation into protoplasts in the cells of maize under Cd stress [18]. The way by which Si enhances the growth of plants exposed to Cd might to some degree be explained by the increased production of biomass and photosynthesis rate attributed to the enhanced formation of thylakoid induced by exogenous addition of Si [17]. In basil, Si addition was found to lower the content of Cd and raise the levels of protective compounds to alleviate the adverse impact of Cd stress [19]. According to previous studies, the role of Si as a supplement that reduces the negative impacts of toxic metal elements was also reported for zinc [20,21], aluminum [22,23,24], copper [25,26], chromium [27,28] and manganese [29].
Forest ecosystems are now being seriously contaminated by Cd pollution derived from industrial effluent, fertilization, application of pesticide, irrigation and so on [1]. Schima superba (Schima superba Gardn), Chinese sweetgum (Liquidambar formosana Hance) and Chinese fir (Cunninghamia lanceolata) are three main afforestation tree species in southern China which can better represent the local forest situations. At present, most studies are mainly focus on crop plants in regard to the mitigation effects of silicon on heavy metal elements rather than woody plants. In this study, we carried out a one-year experiment at Zhangdun nursery, located in Shunchang, Nanping, Fujian province to investigate the effect of Cd stress as well as the mitigation mechanisms of Si addition on woody plants. The aims of this study were: (1) To investigate the impact of Cd stress on growth parameters (height, ground diameter, leaf biomass production, leaf morphological characteristics), chlorophyll content, antioxidant enzyme (SOD, POD, CAT) activities, bioconcentration factor (BCF) values and translocation factor (TF) values of the three kinds of afforestation tree species seedlings; (2) to identify the role of Si on Cd detoxification and the mechanisms involved in Si mitigating Cd stress in woody plants. This study provides an insight into the Cd contamination in forests and paves a way for managers to alleviate Cd stress in forest ecosystem.

2. Materials and Methods

2.1. Study Area

This study was carried out at the Zhangdun nursery of Shunchang, Nanping, Fujian, China, with a mean annual temperature of 18–20 °C and a mean annual precipitation of 1650 mm.

2.2. Experimental Design

Chinese fir, Chinese sweetgum and Schima superba seedlings were chosen as experimental materials in this study. Chemical properties of the soil are: pH 6.85, 0.12 g·kg−1 of organic matter, 0.03 g·kg−1 of available phosphorus, 0.1 g·kg−1 of available potassium and 0.09 mg·kg−1 of cadmium.
Each kind of seedlings with the same height, DBH (diameter at breast height) and canopy were selected to a total number of 60, and were planted in pots (23 cm × 14.5 cm) which contained 5 kg of soil. No exogenous additives but water were added to the seedlings during the growth period.
Ten treatments with six repetitions were employed during the experimental period. Five levels of cadmium supply (0 mg·kg−1, 6 mg·kg−1, 12 mg·kg−1, 24 mg·kg−1, 36 mg·kg−1) were added to the soil in the form of CdCl2·2.5H2O. One level of silicon (1 g·kg−1) was added in the form of soluble silicon fertilizer. (SiO2 ≥ 50%) (Table 1) Water was supplemented to the samples according to the growth situation. After a year, the samples were all collected for measurements and assays.

2.3. Measurements

2.3.1. Determination of Growth Parameters

After harvesting, heights were measured using a typeline and the ground diameter of the samples were measured using a vernier caliper. In order to determine the fresh weight, the samples were rinsed, wiped dry with filter paper and weighed. To determine the dry weight, the samples were dried at the temperature of 65 °C in the drying oven for 72 h to a constant weight. For measuring the leaf areas of the sample, five leaves were randomly taken from each sample and scanned by the scanner (EPSON V39, Zhejiang, China). The length and width area were measured using the software Image J.

2.3.2. Determination of Enzyme Activities and Chlorophyll Content

The fresh leaf samples were frozen by liquid nitrogen for determination of enzyme activities immediately after harvesting. Then, leaf samples were weighed, thoroughly grinded into powder and mixed with 1 mL of extracting solution. The homogenate was subsequently centrifuged at 8000× g, 4 °C for 10 min and was filtered after precipitation. Afterward, the solutions were added following the manufacturer’s instructions on the kit.
The activity of superoxide dismutase (SOD) was assayed according to the method proposed by Giannopolitis and Ries [30] with some modifications. Peroxidase (POD) was measured according to the method proposed by Chance and Maehly [31]. To determine catalase (CAT), the method described by Beers and Sizer [32] was employed, in which the consumption of H2O2 was used to determine the increase of the absorbance at 240 nm. Malondialdehyde (MDA) was assayed according to the method illustrated by Heath and Packer. [33], where the absorbance was determined at 532 nm and adjusted by subtracting the value measured at 600 nm. The method for assaying the chlorophyll content was given by Al-aghabary et al. [34].

2.3.3. Determination of Cd Concentrations, Translocation Factor (TF) and Bioconcentration Factor (BCF)

Different fractions of the samples (leaves and roots shoots) were digested through the microwave digestion instrument after being mixed with HNO3 and H2O2, and the Cd concentrations in different fractions were measured through atomic absorbance spectrometry (TAS-990). To determine the Cd concentrations in soil, 1 g of dried soil sample was sieved through a 2 mm sieve and then was digested with HNO3 and HClO4 in the proportion of 4:1 using the microwave digestion instrument. The Cd concentrations were measured through the atomic absorbance spectrometry (TAS-990). The translocation factor (TF) values and bioconcentation factor (BCF) values were calculated according to the method proposed by Sozoniuk et al. [35].

2.3.4. Statistical Analysis

The statistical analysis was carried out using the IBM SPSS Statistics 25. Means and standard deviations were calculated for each treatment. The significant differences were analyzed using the one way ANOVA followed by the Turkey test, at the probability level of 0.05. Graphs in this study were produced using the software Origin 2021.

3. Results

3.1. Effects of Cd and Si on Growth Parameters of Three Kinds of Tree Specie Seedlings

Figure 1 indicates the growth parameters of the three target tree species seedlings under different levels of Cd stress treated with or without Si. Cd stress caused decreases in the heights and ground diameters of the tree target species seedlings. Under 36 mg·kg−1 Cd treatment, which is the highest treatment in our study, both the heights and the ground diameters decreased the most. Conversely, Si addition increased the heights and ground diameters of the target species seedlings. The increases were rather significant under 12–36 mg·kg−1 Cd treatments. (Heights: 30.81%, 18.85%, 26.45% and ground diameters: 16.21%, 15.44%, 22.36% for Schima superba, Chinese sweetgum and Chinese fir, respectively).
Leaf lengths, widths and areas of Schima superba and Chinese fir seedlings all decreased significantly in Schima superba seedlings except under 6 mg·kg−1 Cd treatment, whereas the situation was not the same for Chinese sweetgum seedlings, in which leaf lengths, widths and areas were all observed to decrease significantly compared to the controls under 6 mg·kg−1 and 12 mg·kg−1 Cd treatments. The addition of Si promoted the growth of leaf lengths, widths and areas in the three target specie seedlings, though the growth of leaf traits did not differ significantly under 6 mg·kg−1 Cd treatment with or without Si addition.
Si significantly promoted the biomass production of the three kinds of tree species seedlings, which implied the beneficial effect of Si application. The leaf dry weight and fresh weight production of Schima superba and Chinese sweetgum seedlings were stimulated by 6 mg·kg−1 Cd treatment, while both decreased with the increasing Cd treatments and reached their minimum under 36 mg·kg−1 Cd treatment. However, instead of stimulating dry weight and fresh weight productions, Cd stresses were only observed to decrease biomass production of Chinese fir seedlings. Added Si imposed a growth-promoting effect, which facilitated both biomass productions of the three kinds of target species seedlings.

3.2. Effects of Cd and Si Antioxidative Enzyme Activities

As shown in Figure 2, Cd treatments caused both a stimulative and inhibitory effect on antioxidative enzyme activities, while both effects differed among treatments and species. Exogenous Si application played a beneficial role in enhancing the activities. SOD activities of the three target tree species seedlings were all stimulated by Cd stress under 12 mg·kg−1 Cd treatment and the ones of Chinese sweetgum and Chinese fir seedlings still remained higher than the controls under 24 mg·kg−1 Cd treatment. POD activities of Schima superba seedlings were stimulated, but not significantly, under 6 mg·kg−1 Cd treatment and finally decreased by 57.81% under 36 mg·kg−1 Cd treatment. The stimulatory effects of Cd on POD activities were observed in Chinese sweetgum seedlings under 12 mg·kg−1 Cd treatment and in Chinese fir seedlings under 6−24 mg·kg−1 Cd treatments. Also, 36 mg·kg−1 Cd treatment caused a significant decline in the activities of POD in Chinese sweetgum and Chinese fir seedlings as compared to the controls. For CAT activities, those in Schima superba and Chinese sweetgum seedlings were stimulated by Cd stress under 12 mg·kg−1 Cd treatment, whereas the ones in Chinese fir seedlings were only observed to decrease under 12–36 mg·kg−1 Cd treatments.
In general, the application of Si imposed a positive effect on the three target specie seedlings, enhancing the activities of the enzymes under Cd stress.

3.3. Effects of Cd and Si on Malondialdehyde (MDA) Content

As shown in Figure 3, increasing Cd levels resulted in the increase of MDA concentration, and the contents were greatest under 36 mg·kg−1 Cd treatment (increased by 60.75%, 44.91%, 49%, respectively, for Schima superba, Chinese sweetgum and Chinese fir), which was the highest treatment in this study. In contrast, exogenously addition of Si caused declines in MDA contents under different levels of Cd treatments.

3.4. Effects of Cd and Si on Chlorophyll Content

Figure 4 shows that Cd stress significantly decreased the content of chlorophyll a, chlorophyll b and the total chlorophyll content of the three target specie seedlings; while the reverse was true for Si application. Overall, Cd stress declined the contents of chlorophyll a and chlorophyll b, and, as a consequence, the total chlorophyll content. Additionally, high treatment of Cd (36 mg·kg−1) induced the greatest reduction of all relative to the controls for all the three contents in the target species seedlings. Addition of Si, on the other hand, caused a positive effect, increasing the contents of chlorophyll a and b, and thus the content of total chlorophyll Also, the chlorophyll a/b ratio decreased under Cd stress, whereas the addition of Si did not ameliorate this trend.

3.5. Effects of Cd and Si on Soil PH

Soil PH decreased significantly under Cd stress, while the trend was opposite after Si addition (Figure 5). Specifically, for Schima superba, soil PH values of the seedlings treated with Si increased by 3.06%, 1.9% and 1.26%, respectively, compared to those non-Si−treated ones (6, 24 and 36 mg·kg−1 Cd treatment). Additionally, Soil PH values in Chinese sweetgum seedlings increased by 5.25%, 3.93%, 4.43%, and 4.72%, respectively (6, 12, 24 and 36 mg·kg−1 Cd treatment). For Chinese fir seedlings, soil PH values were 3.52% and 5.09% higher than non-Si−treated ones (24 and 36 mg·kg−1 Cd treatment, respectively).

3.6. Effects of Cd and Si on Cd Concentration of Different Fractions of Seedlings and Translocation Factor (TF) Values and Bioconcentration Factor (BCF) Values

The Cd concentrations of different fractions of seedlings under different levels of Cd treatments treated with or without Si and the translocation factor (TF) and bioconcentration factor (BCF) obtained for the three kinds of tree species seedlings are shown in Table 2, Table 3 and Table 4. For the three species seedlings, Cd stress hardly affected Cd concentration in root stems and leaves under 6 mg·kg−1 Cd treatment, while they all saw a significant increase under 12–36 mg·kg−1 Cd treatments as compared to the controls. (Table 2) Application of Si significantly decreased the Cd concentration in different fractions of seedlings. As Cd levels increased, the BCF values increased significantly for all parts of Schima superba and Chinese fir seedlings, as well as for the roots and stems of Chinese sweetgum seedlings, whereas the BCF values of leaves of Chinese sweetgum under 24–36 mg·kg−1 Cd treatments were all lower than the value under 6 mg·kg−1 Cd treatment. (Table 3) After Si addition, the BCF values decreased significantly for all fractions of the three tree species. The root−to−stem TF values were all observed to increase under Cd treatments compared to the control in the three kinds of tree species seedlings, whereas the root−to−leaf TF values decreased with the rise of Cd treatments. (Table 3) TF values of the three kinds of tree species seedlings were generally not affected by Si application, except for the root-to-stem TF values of Schima superba seedlings, which decreased by 32% under 6 mg·kg−1 Cd treatment, the root−to−leaf TF value of Chinese sweetgum seedlings, which increased by 52.88% under 36 mg·kg−1 Cd treatment, and the root−to−stem TF value of Chinese fir, which increased by 78.03% and 38.25% under 6 mg·kg−1 and 36 mg·kg−1 Cd treatments, respectively.

4. Discussion

Here, we tested how Cd stress and the addition of Si affect three tree species in southern China. The negative impact of Cd on growth is apparent from the decreases in heights, ground diameters, leaf biomass productions and leaf morphological parameters of all the three target species seedlings (Schima superba, Chinese sweetgum and Chinese fir). The deficiency of nutrition and reduction of water imbibition induced by toxic heavy metal stress negatively affected the metabolic activities, thereby declining the plant growth. Similar results were also demonstrated by a study on oak seedlings [36]. According to a previous study, the decline of growth parameters is the initial symptom through which heavy metal toxicity begins to manifest itself [37]. In our cases, though 6 mg·kg−1 Cd treatment mostly did not affect the growth of heights, ground diameters and leaf morphological traits, all of which markedly decreased as the treatments increased (Figure 1). For leaf biomass production, a stimulatory effect that was corroborated also by Zorrig et al. [38] was detected in Schima superba and Chinese sweetgum seedlings, which indicates a protection against the initial levels of toxic heavy metal stress. However, Cd stress was beyond the capacity of protection derived from the seedlings as the Cd levels increased, and thus caused a decrease in leaf biomass protection. Noteworthy, the leaf dry weight fresh weight production of Chinese fir seedlings was not stimulated by Cd stress. Given so, we speculate that the leaf biomass production of Chinese fir might be stimulated by a Cd level lower than 6 mg·kg−1. Moreover, our study also showed that heights, ground diameters, leaf morphological parameters and biomass production of the three target species seedlings increased significantly in response to Si addition, which indicated the beneficial effect of Si on the growth of the seedlings—corroborated by a previous study, in which Si addition alleviated the depression of growth parameters including leaf length, leaf area, root length and biomass, caused by Cd stress [39].
Our results showed that chlorophyll a, chlorophyll b and total chlorophyll content of the three kinds of tree species seedlings decreased significantly under Cd stress. A similar result was found by Duan et al. [40], who demonstrated that chlorophyll of Cd-exposed seedlings decreased significantly compared to the non-Cd−treated ones. Mechanisms of Cd−induced reduction in chlorophyll contents were also studied. To be specific, Cd stress attenuates the uptake of nutrient, which inhibits Mg2+ inserting into protoporphyrinogen, thereby affecting the synthesis of chlorophyll [41]; additionally, Cd2+ can be used as a substitution of Mg2+ due to their similar charges, causing reductions in the biosynthesis of chlorophyll a and chlorophyll b [41,42]. Treatment with Si significantly increased the content of chlorophyll a and chlorophyll b, and thus the total chlorophyll (Figure 4). Si plays a key functional role in mitigating photosynthesis inhibition caused by Cd stress [43,44]. Furthermore, a mitigation effect of Si on photosynthetic inhibition induced by Cd stress contributed to the growth of biomass production, which means that addition of Si causes the increase of biomass production as a consequence of the increase of chlorophyll content [43]. This outcome is in agreement with our study (Figure 1 and Figure 4). The chlorophyll a/b ratio also declined relative to the control under Cd stress, However, we found no evidence that addition of Si mediated the negative effect of Cd stress on chlorophyll a/b ratio. In fact, high concentrations of Cd may do more damage to the content of chlorophyll a than to chlorophyll b. However, due to the experiment period not being long enough, we did not observe any amelioration on chlorophyll a/b ratio. Further research is thus needed to shed more light on the effect of Si addition on chlorophyll a/b in long-term experiments. Plants spontaneously developed a cellular antioxidant system in order to minimize the impact of oxidative stress [45], which is mainly composed of SOD, POD and CAT [46]. The enzymatic system, in which SOD plays an important role in catalyzing the radical O2 to H2O2 and molecular oxygen, and POD and CAT both serve as a catalyzer for catalyzing the superoxide and H2O2 to H2O and O2 [47], acts directly by scavenging the reactive oxygen species (ROS) or produces a non-enzymatic antioxidant [48]. According to previous studies, imposition of Cd stress caused declines in SOD, POD and CAT activities [49,50]. Not surprisingly, we found that POD and CAT activities of Schima superba and Chinese fir seedlings decreased relative to the controls (Figure 2). Besides, SOD, POD and CAT activities were observed to be stimulated by Cd stress in our cases. This is actually in line with a corroborating study that showed that low concentrations of Cd treatment may stimulate antioxidant enzyme activities so as to protect plants against oxidative stress [51]. Conversely, high concentrations of Cd treatment would damage the structure of enzymes and affect the synthesis of antioxidant enzymes, by which the protective system would be diminished. Even under 36 mg kg−1 Cd treatment, antioxidant enzyme (SOD, POD, CAT) activities of Chinese sweetgum were not lower than the controls, which implied that the Cd toxicity thresholds of SOD, POD and CAT activities of Chinese sweetgum were higher than 36 mg·kg−1. In addition, our study also supported the finding that application of Si promotes the activities of antioxidant enzymes in order to resist the adverse impact of Cd toxicity in plants [50,52] (Figure 2). The stimulative effects of Si facilitate the formation of antioxidant enzyme, thereby enhancing the plants’ ability to resist the Cd−induced oxidative stress. Additionally, a mitigation effect of Si was reported to alleviate the stress caused by toxic heavy metals such as Zn, Pb and Mn by stimulating the antioxidant enzyme activities [53]. It is well documented that instead of producing ROS directly, Cd stress generates oxidative burst by means of interfering with the cellular antioxidant system, which may result in the production of lipid peroxidation and thus increases the content of MDA. [54,55] Therefore, the content of MDA serves as a determinant for lipid peroxidation in plants. In line with this, we found that increasing levels of Cd treatments stimulated the MDA productions in contrast to the non−Si−treated ones. Together with the results, we concluded that in the three target species seedlings, enhanced activities of SOD POD and CAT alleviated oxidative stress, and thus prohibited the production of lipid peroxidation. In this way, the content of MDA was diminished (Figure 2 and Figure 3).
The translocation factor (TF) represents the capacity of toxic heavy metal element transfer from roots to different fractions of plants; the bioconcentration factor (BCF) represents the levels of heavy metal element concentrations in plants [56]. Toxic heavy metal elements can be absorbed by plant roots and subsequently be translocated from roots to different fractions. Our cases showed that as the Cd levels increased, Cd concentrations of different fractions (root, stem, leaf) of the three kinds of tree species all increased markedly compared to the controls, with leaves accumulating the lowest concentration of Cd. (Table 2) This result is in agreement with a study suggesting that low Cd concentration in leaves might be a strategy for plants to protect photosynthetic organs from oxidative stress induced by Cd [57], The incremental Cd treatments induced the rise of BCF values in contrast with the controls, except for the leaf BCF values in Chinese sweetgum, which were lower than the control under 24 and 36 mg kg−1 Cd treatments. (Table 4) Noteworthy, unlike the root-to-stem TF values, which significantly increased under different Cd treatments, the root-to-leaf TF values decreased significantly compared to the controls (Table 3). Similarly, Sozoniuk et al. [36] explained that decreased values of leaf root−to−leaf TF indicated a diminished capacity to translocate Cd to photosynthetic organs, suggesting a way for plants to cope with Cd stress. The present study also showed that the Si concentration of different fractions in Si-treated seedlings was higher than in non−Si−treated ones. This phenomenon, shown also by a previous study [56], is attributable to the enhanced defense of the seedlings against Cd stress. Treatment with Si significantly decreased the content of Cd in roots, stems and leaves; also, this trend was true for the BCF values. The detoxification mechanism of Si for inhibition of toxic metal uptake was investigated: (1) by inducing toxic metal ions to create a bond with root cell walls and deposit lignin, Si effectively inhibits the uptake of toxic metals in plants [58]. (2) Si can form complexes with toxic metal ions in roots and soil and thus inhibits the uptake of toxic metal [59]. So, together with these results, we speculated that Si might bond Cd ions with cell walls and form complexes with Cd in order to lower the Cd concentration in the three target tree species seedlings. In general, the root−to−leaf and root-to-stem TF values were not affected by Si addition (Table 3). The root-to-stem TF values of Schima superba seedlings under 6 mg kg−1 were higher than those of the Si-treated ones, whereas the root-to-leaf TF values of Chinese sweetgum seedlings under 36 mg kg−1 Cd treatment and the root−to−stem TF values of Chinese fir seedlings were all lower than those of the Si-treated ones. The inconsistent variations of TF values indicated the influences of other factors on the mitigation effect of Si on Cd stress. So, we conjectured that instead of inhibiting the translocation of Cd, the addition of Si mitigates Cd stress mainly by inhibiting the uptake of Cd. It has been frequently suggested that soil pH is negatively correlated with toxic metal availability and mobility in soil. Not surprisingly, our study echoed some of the previous empirical studies. (Figure 4). For instance, Dong et al. [56] corroborated that Cd stress increased the acidity of soil, while the application of Si could counteract the negative impact of Cd on soil PH. So, together with the results above, we concluded that the Si−related amendment of Cd toxicity in the three target tree species seedlings is in connection with the increase of soil pH and the reduction of availability and uptake of Cd.

5. Conclusions

According to our current study, Cd stress could significantly decrease growth parameters, including heights, ground diameter, leaf morphological parameters, biomass production, chlorophyll contents and chlorophyll a/b ratio in the three kinds of tree species seedlings. Cd stress could stimulate the antioxidant enzyme activities (SOD, POD, CAT), whereas the activities might be diminished as the Cd treatments increased. Cd treatments induced the incremental increase in MDA content due to the increase of ROS production in the seedlings. The BCF values of the three kinds of seedlings mostly increased with the rise of Cd treatments, except for the leaf BCF value of Chinese sweetgum. Root−to−stem TF values increased under Cd treatments, while Cd treatments induced a decrease in the root−to−leaf TF values of the three kinds of seedlings. Soil PH values also decreased under Cd stress. Si plays an important role in mitigating Cd stress. The mechanisms by which Si mitigates Cd toxicity involved in this study are: (1) enhancing the growth parameters of seedlings and increasing the chlorophyll contents. (2) Stimulating the formation of antioxidant enzymes so as to scavenge the excessive production of ROS and decreasing the content of MDA. (3) Increasing the Si concentration of different fractions of seedlings. (4) Inhibiting the uptake of Cd from soil by the seedlings and increasing soil pH. To summarize, Si addition is beneficial to Schima superba, Chinese sweetgum and Chinese fir seedlings, alleviating the adverse impact induced by Cd stress.

Author Contributions

Conceptualization, S.J. and D.Z.; methodology, S.J. and D.Z.; software, Z.W.; validation, S.J. and D.Z.; formal analysis, Z.W. and S.J.; data curation, Z.W., Y.S., D.H., Y.W., Y.C. and C.L.; writing—original draft preparation, Z.W., X.L., D.Z. and S.J.; writing—review and editing, Z.W., Y.S., D.H., Y.W., Y.C., C.L., X.L., D.Z. and S.J.; visualization, Z.W.; supervision, S.J. and D.Z.; project administration, D.Z.; funding acquisition, D.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research is funded by the National Natural Science Foundation of China (Project Nos. 32071760 and 41701099), and the Fujian Forestry Science and Technology Project (2022FKJ02).

Institutional Review Board Statement

No applicable.

Informed Consent Statement

No applicable.

Data Availability Statement

No applicable.

Conflicts of Interest

The authors declare no competing interests.

References

  1. Das, P.; Samantaray, S.; Rout, G. Studies on cadmium toxicity in plants: A review. Environ. Pollut. 1997, 98, 29–36. [Google Scholar] [CrossRef]
  2. Kieffer, P.; Schröder, P.; Dommes, J.; Hoffmann, L.; Renaut, J.; Hausman, J.-F. Proteomic and enzymatic response of poplar to cadmium stress. J. Proteom. 2009, 72, 379–396. [Google Scholar] [CrossRef] [PubMed]
  3. Ali, B.; Qian, P.; Jin, R.; Ali, S.; Khan, M.; Aziz, R.; Tian, T.; Zhou, W. Physiological and ultra-structural changes in Brassica napus seedlings induced by cadmium stress. Biol. Plant. 2014, 58, 131–138. [Google Scholar] [CrossRef]
  4. Arduini, I.; Godbold, D.L.; Onnis, A. Cadmium and copper uptake and distribution in Mediterranean tree seedlings. Physiol. Plant. 1996, 97, 111–117. [Google Scholar] [CrossRef]
  5. EF, A.A.; Abeer, H.; Alqarawi, A.; Hend, A.A. Alleviation of adverse impact of cadmium stress in sunflower (Helianthus annuus L.) by arbuscular mycorrhizal fungi’. Pak. J. Bot. 2015, 47, 785–795. [Google Scholar]
  6. Karyotis, T.; Iliadis, C.; Noulas, C.; Mitsibonas, T. Preliminary research on seed production and nutrient content for certain quinoa varieties in a saline–sodic soil. J. Agron. Crop Sci. 2003, 189, 402–408. [Google Scholar] [CrossRef]
  7. Qiu, T.; Andrus, R.; Aravena, M.-C.; Ascoli, D.; Bergeron, Y.; Berretti, R.; Berveiller, D.; Bogdziewicz, M.; Boivin, T.; Bonal, R.; et al. Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery. Nat. Commun. 2022, 13, 2381. [Google Scholar] [CrossRef] [PubMed]
  8. Qiu, T.; Sharma, S.; Woodall, C.W.; Clark, J.S. Niche Shifts from Trees to Fecundity to Recruitment That Determine Species Response to Climate Change. Front. Ecol. Evol. 2022, 9, 719141. [Google Scholar] [CrossRef]
  9. Richards, A.E.; Forrester, D.I.; Bauhus, J.; Scherer-Lorenzen, M.J.T.P. The influence of mixed tree plantations on the nutrition of individual species: A review. Tree Physiol. 2010, 30, 1192–1208. [Google Scholar] [CrossRef] [Green Version]
  10. Ma, J.F. Role of silicon in enhancing the resistance of plants to biotic and abiotic stresses. Soil Sci. Plant Nutr. 2004, 50, 11–18. [Google Scholar] [CrossRef]
  11. Verma, K.K.; Song, X.-P.; Tian, D.-D.; Guo, D.-J.; Chen, Z.-L.; Zhong, C.-S.; Nikpay, A.; Singh, M.; Rajput, V.D.; Singh, R.K.; et al. Influence of Silicon on Biocontrol Strategies to Manage Biotic Stress for Crop Protection, Performance, and Improvement. Plants 2021, 10, 2163. [Google Scholar] [CrossRef] [PubMed]
  12. Fauteux, F.; Rémus-Borel, W.; Menzies, J.G.; Bélanger, R.R. Silicon and plant disease resistance against pathogenic fungi. FEMS Microbiol. Lett. 2005, 249, 1–6. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  13. Bhat, J.A.; Shivaraj, S.M.; Singh, P.; Navadagi, D.B.; Tripathi, D.K.; Dash, P.K.; Solanke, A.U.; Sonah, H.; Deshmukh, R. Role of silicon in mitigation of heavy metal stresses in crop plants. Plants 2019, 8, 71. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  14. Mvondo-She, M.A.; Gatabazi, A.; Laing, M.D.; Ndhlala, A.R. A Review on the Role of Silicon Treatment in Biotic Stress Mitigation and Citrus Production. Agronomy 2021, 11, 2198. [Google Scholar] [CrossRef]
  15. Adrees, M.; Ali, S.; Rizwan, M.; Zia-Ur-Rehman, M.; Ibrahim, M.; Abbas, F.; Farid, M.; Qayyum, M.F.; Irshad, M.K. Mechanisms of silicon-mediated alleviation of heavy metal toxicity in plants: A review. Ecotoxicol. Env. Saf. 2015, 119, 186–197. [Google Scholar] [CrossRef] [PubMed]
  16. Guo, L.; Chen, A.; He, N.; Yang, D.; Liu, M. Exogenous silicon alleviates cadmium toxicity in rice seedlings in relation to Cd distribution and ultrastructure changes. J. Soils Sediments 2017, 18, 1691–1700. [Google Scholar] [CrossRef]
  17. Vaculik, M.; Pavlovic, A.; Lux, A. Silicon alleviates cadmium toxicity by enhanced photosynthetic rate and modified bundle sheath’s cell chloroplasts ultrastructure in maize. Ecotoxicol. Environ. Saf. 2015, 120, 66–73. [Google Scholar] [CrossRef]
  18. Kollárová, K.; Kusá, Z.; Vatehová-Vivodová, Z.; Lišková, D. The response of maize protoplasts to cadmium stress mitigated by silicon. Ecotoxicol. Environ. Saf. 2018, 170, 488–494. [Google Scholar] [CrossRef]
  19. Gheshlaghpour, J.; Asghari, B.; Khademian, R.; Sedaghati, B. Silicon alleviates cadmium stress in basil (Ocimum basilicum L.) through alteration of phytochemical and physiological characteristics. Ind. Crops Prod. 2021, 163, 113338. [Google Scholar] [CrossRef]
  20. Gu, H.-H.; Zhan, S.-S.; Wang, S.-Z.; Tang, Y.-T.; Chaney, R.L.; Fang, X.-H.; Cai, X.-D.; Qiu, R.-L. Silicon-mediated amelioration of zinc toxicity in rice (Oryza sativa L.) seedlings. Plant Soil 2012, 350, 193–204. [Google Scholar] [CrossRef] [Green Version]
  21. Kaya, C.; Tuna, A.L.; Sonmez, O.; Ince, F.; Higgs, D. Mitigation effects of silicon on maize plants grown at high zinc. J. Plant Nutr. 2009, 32, 1788–1798. [Google Scholar] [CrossRef]
  22. de Jesus, L.R.; Batista, B.L.; da Silva Lobato, A.K. Silicon reduces aluminum accumulation and mitigates toxic effects in cowpea plants. Acta Physiol. Plant. 2017, 39, 1–14. [Google Scholar] [CrossRef]
  23. de Freitas, L.B.; Fernandes, D.M.; Maia, S.C.M.; Fernandes, A.M. Effects of silicon on aluminum toxicity in upland rice plants. Plant Soil 2017, 420, 263–275. [Google Scholar] [CrossRef] [Green Version]
  24. Dorneles, A.O.S.; Pereira, A.S.; Sasso, V.M.; Possebom, G.; Tarouco, C.P.; Schorr, M.R.W.; Rossato, L.; Ferreira, P.A.A.; Tabaldi, L.A. Aluminum stress tolerance in potato genotypes grown with silicon. Bragantia 2019, 78, 12–25. [Google Scholar] [CrossRef] [Green Version]
  25. El-Beltagi, H.S.; Sofy, M.R.; Aldaej, M.I.; Mohamed, H.I. Silicon alleviates copper toxicity in flax plants by up-regulating antioxidant defense and secondary metabolites and decreasing oxidative damage. Sustainability 2020, 12, 4732. [Google Scholar] [CrossRef]
  26. Bosnić, D.; Nikolić, D.; Timotijević, G.; Pavlović, J.; Vaculík, M.; Samardžić, J.; Nikolić, M. Silicon alleviates copper (Cu) toxicity in cucumber by increased Cu-binding capacity. Plant Soil 2019, 441, 629–641. [Google Scholar] [CrossRef]
  27. Alam, P.; Balawi, T.H.; Altalayan, F.H.; Hatamleh, A.A.; Ashraf, M.; Ahmad, P. Silicon attenuates the negative effects of chromium stress in tomato plants by modifying antioxidant enzyme activities, ascorbate–glutathione cycle and glyoxalase system. Acta Physiol. Plant. 2021, 43, 1–17. [Google Scholar] [CrossRef]
  28. Sarkar, U.; Tahura, S.; Das, U.; Amin Mintu, M.R.; Humayan Kabir, A. Mitigation of chromium toxicity in wheat (Triticum aestivum L.) through silicon. Gesunde Pflanz. 2020, 72, 237–244. [Google Scholar] [CrossRef]
  29. Li, P.; Song, A.; Li, Z.; Fan, F.; Liang, Y. Silicon ameliorates manganese toxicity by regulating both physiological processes and expression of genes associated with photosynthesis in rice (Oryza sativa L.). Plant Soil 2015, 397, 289–301. [Google Scholar] [CrossRef]
  30. Fridovich, I. Superoxide dismutases. Annu. Rev. Biochem. 1975, 44, 147–159. [Google Scholar] [CrossRef]
  31. Chance, B.; Maehly, A. [136] Assay of catalases and peroxidases. Methods Enzymol. 1955, 2, 764–775. [Google Scholar] [CrossRef]
  32. Beers, R.F.; Sizer, I.W. A spectrophotometric method for measuring the breakdown of hydrogen peroxide by catalase. J. Biol. Chem. 1952, 195, 133–140. [Google Scholar] [CrossRef]
  33. Heath, R.L.; Packer, L. Photoperoxidation in isolated chloroplasts: I. Kinetics and stoichiometry of fatty acid peroxidation. Arch. Biochem. Biophys. 1968, 125, 189–198. [Google Scholar] [CrossRef]
  34. Al-aghabary, K.; Zhu, Z.; Shi, Q. Influence of silicon supply on chlorophyll content, chlorophyll fluorescence, and antioxidative enzyme activities in tomato plants under salt stress. J. Plant Nutr. 2005, 27, 2101–2115. [Google Scholar] [CrossRef]
  35. Sozoniuk, M.; Nowak, M.; Dudziak, K.; Leśniowska-Nowak, J.; Kowalczyk, K. Quercus robur as a Potential Cd Phytostabilizator. Russ. J. Plant Physiol. 2020, 67, 294–302. [Google Scholar] [CrossRef]
  36. Kahle, H. Response of roots of trees to heavy metals. Environ. Exp. Bot. 1993, 33, 99–119. [Google Scholar] [CrossRef]
  37. Domínguez, M.T.; Madrid, F.; Marañón, T.; Murillo, J.M. Cadmium availability in soil and retention in oak roots: Potential for phytostabilization. Chemosphere 2009, 76, 480–486. [Google Scholar] [CrossRef] [PubMed]
  38. Zorrig, W.; El Khouni, A.; Ghnaya, T.; Davidian, J.-C.; Abdelly, C.; Berthomieu, P. Lettuce (Lactuca sativa): A species with a high capacity for cadmium (Cd) accumulation and growth stimulation in the presence of low Cd concentrations. J. Hortic. Sci. Biotechnol. 2013, 88, 783–789. [Google Scholar] [CrossRef]
  39. Vaculík, M.; Lux, A.; Luxová, M.; Tanimoto, E.; Lichtscheidl, I. Silicon mitigates cadmium inhibitory effects in young maize plants. Environ. Exp. Bot. 2009, 67, 52–58. [Google Scholar] [CrossRef]
  40. Duan, C.; Wu, S.; Sang, Y.; Bahetibieke, W.; Ru, J.; Song, J.; Cui, X. Exogenous succinic acid mediates responses of Larix olgensis A. Henry to cadmium stress. Int. J. Phytoremediation 2019, 21, 742–751. [Google Scholar] [CrossRef]
  41. Parmar, P.; Kumari, N.; Sharma, V. Structural and functional alterations in photosynthetic apparatus of plants under cadmium stress. Bot. Stud. 2013, 54, 1–6. [Google Scholar] [CrossRef]
  42. Küpper, H.; Küpper, F.; Spiller, M. In situ detection of heavy metal substituted chlorophylls in water plants. Photosynth. Res. 1998, 58, 123–133. [Google Scholar] [CrossRef]
  43. Wu, J.-W.; Shi, Y.; Zhu, Y.-X.; Wang, Y.-C.; Gong, H.-J. Mechanisms of enhanced heavy metal tolerance in plants by silicon: A review. Pedosphere 2013, 23, 815–825. [Google Scholar] [CrossRef]
  44. Rizwan, M.; Meunier, J.-D.; Davidian, J.-C.; Pokrovsky, O.; Bovet, N.; Keller, C. Silicon alleviates Cd stress of wheat seedlings (Triticum turgidum L. cv. Claudio) grown in hydroponics. Environ. Sci. Pollut. Res. 2016, 23, 1414–1427. [Google Scholar] [CrossRef] [PubMed]
  45. Dixit, V.; Pandey, V.; Shyam, R. Differential antioxidative responses to cadmium in roots and leaves of pea (Pisum sativum L. cv. Azad). J. Exp. Bot. 2001, 52, 1101–1109. [Google Scholar] [CrossRef] [Green Version]
  46. Apel, K.; Hirt, H. Reactive oxygen species: Metabolism, oxidative stress, and signal transduction. Annu. Rev. Plant Biol. 2004, 55, 373–399. [Google Scholar] [CrossRef] [Green Version]
  47. Sofy, A.R.; Dawoud, R.A.; Sofy, M.R.; Mohamed, H.I.; Hmed, A.A.; El-Dougdoug, N.K. Improving regulation of enzymatic and non-enzymatic antioxidants and stress-related gene stimulation in Cucumber mosaic cucumovirus-infected cucumber plants treated with glycine betaine, chitosan and combination. Molecules 2020, 25, 2341. [Google Scholar] [CrossRef] [PubMed]
  48. Yang, F.; Xu, X.; Xiao, X.; Li, C. Responses to drought stress in two poplar species originating from different altitudes. Biol. Plant. 2009, 53, 511–516. [Google Scholar] [CrossRef]
  49. Muradoglu, F.; Gundogdu, M.; Ercisli, S.; Encu, T.; Balta, F.; Jaafar, H.Z.; Zia-Ul-Haq, M. Cadmium toxicity affects chlorophyll a and b content, antioxidant enzyme activities and mineral nutrient accumulation in strawberry. Biol. Res. 2015, 48, 1–7. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  50. Farooq, M.A.; Ali, S.; Hameed, A.; Ishaque, W.; Mahmood, K.; Iqbal, Z. Alleviation of cadmium toxicity by silicon is related to elevated photosynthesis, antioxidant enzymes; suppressed cadmium uptake and oxidative stress in cotton. Ecotoxicol. Environ. Saf. 2013, 96, 242–249. [Google Scholar] [CrossRef]
  51. Wang, Y.; Yan, A.; Dai, J.; Wang, N.; Wu, D. Accumulation and tolerance characteristics of cadmium in Chlorophytum comosum: A popular ornamental plant and potential Cd hyperaccumulator. Environ. Monit. Assess. 2012, 184, 929–937. [Google Scholar] [CrossRef] [PubMed]
  52. Mittler, R.; Vanderauwera, S.; Gollery, M.; Van Breusegem, F. Reactive oxygen gene network of plants. Trends Plant Sci. 2004, 9, 490–498. [Google Scholar] [CrossRef]
  53. Fu, Y.-Q.; Shen, H.; Wu, D.-M.; Cai, K.-Z. Silicon-mediated amelioration of Fe2+ toxicity in rice (Oryza sativa L.) roots. Pedosphere 2012, 22, 795–802. [Google Scholar] [CrossRef]
  54. Krantev, A.; Yordanova, R.; Janda, T.; Szalai, G.; Popova, L. Treatment with salicylic acid decreases the effect of cadmium on photosynthesis in maize plants. J. Plant Physiol. 2008, 165, 920–931. [Google Scholar] [CrossRef] [PubMed]
  55. Foyer, C.H.; Noctor, G. Redox homeostasis and antioxidant signaling: A metabolic interface between stress perception and physiological responses. Plant Cell 2005, 17, 1866–1875. [Google Scholar] [CrossRef] [Green Version]
  56. Dong, Q.; Fang, J.; Huang, F.; Cai, K. Silicon amendment reduces soil Cd availability and Cd uptake of two Pennisetum species. Int. J. Environ. Res. Public Health 2019, 16, 1624. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  57. Mingjie, Y.; Xianyong, L.; Xiaoe, Y. Impact or Cd on growth and nutrient accumulation or different plant species. Chin. J. Appl. Ecol. 1998, 9, 89–94. [Google Scholar]
  58. Ma, J.F.; Yamaji, N. Silicon uptake and accumulation in higher plants. Trends Plant Sci. 2006, 11, 392–397. [Google Scholar] [CrossRef] [PubMed]
  59. Hodson, M.J.; Sangster, A. The interaction between silicon and aluminium in Sorghum bicolor (L.) Moench: Growth analysis and X-ray microanalysis. Ann. Bot. 1993, 72, 389–400. [Google Scholar] [CrossRef]
Forests 13 01641 g001 550
Figure 1. Effects of Cd and Si on growth parameters of seedling for (A) Schima superba, (B) Chinese sweetgum, and (C) Chinese fir. Uppercase letter beside each graph represent height, ground diameter, biomass production and leaf morphological traits for (A–D), respectively. Each value is a mean of six repetitions. Lowercase letters above the bars indicates significant differences according to Turkey test (p < 0.05).
Figure 1. Effects of Cd and Si on growth parameters of seedling for (A) Schima superba, (B) Chinese sweetgum, and (C) Chinese fir. Uppercase letter beside each graph represent height, ground diameter, biomass production and leaf morphological traits for (A–D), respectively. Each value is a mean of six repetitions. Lowercase letters above the bars indicates significant differences according to Turkey test (p < 0.05).
Forests 13 01641 g001
Forests 13 01641 g002 550
Figure 2. Effects of Cd and Si on antioxidative enzyme activities of seedlings for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese fir. Each value is a mean of six repetitions. Lowercase letters above the bars indicate significant differences according to the Turkey’s test (p < 0.05).
Figure 2. Effects of Cd and Si on antioxidative enzyme activities of seedlings for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese fir. Each value is a mean of six repetitions. Lowercase letters above the bars indicate significant differences according to the Turkey’s test (p < 0.05).
Forests 13 01641 g002
Forests 13 01641 g003 550
Figure 3. Effects of Cd and Si on MDA contents of seedling for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese fir. Each value is a mean of six repetitions. Lowercase letters above the bars indicate significant differences according to the Turkey’s test (p < 0.05).
Figure 3. Effects of Cd and Si on MDA contents of seedling for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese fir. Each value is a mean of six repetitions. Lowercase letters above the bars indicate significant differences according to the Turkey’s test (p < 0.05).
Forests 13 01641 g003
Forests 13 01641 g004 550
Figure 4. Effects of Cd and Si on chlorophyll a, chlorophyll b, total chlorophyll and chlorophyll a/b ratio of seedling for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese firs. Each value is a mean of six repetitions. Lowercase letters above the bars indicate significant differences according to the Turkey’s test (p < 0.05).
Figure 4. Effects of Cd and Si on chlorophyll a, chlorophyll b, total chlorophyll and chlorophyll a/b ratio of seedling for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese firs. Each value is a mean of six repetitions. Lowercase letters above the bars indicate significant differences according to the Turkey’s test (p < 0.05).
Forests 13 01641 g004
Forests 13 01641 g005 550
Figure 5. Effects of Cd and Si on soil pH of seedlings for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese fir. Lowercase letters above the bars indicate significant differences according to the Turkey’s test. (p < 0.05).
Figure 5. Effects of Cd and Si on soil pH of seedlings for (a) Schima superba, (b) Chinese sweetgum, and (c) Chinese fir. Lowercase letters above the bars indicate significant differences according to the Turkey’s test. (p < 0.05).
Forests 13 01641 g005
Table
Table 1. Treatments for the experiment.
Table 1. Treatments for the experiment.
Numbers of TreatmentsCombinations
1Cd0 Si0Cd0 Si1
2Cd6 Si0Cd6 Si1
3Cd12 Si0Cd12 Si1
4Cd24 Si0Cd24 Si1
5Cd48 Si0Cd48 Si1
Subscripts represent the concentrations of each treatment (e.g., Cd6 indicates that the concentration of Cadmium added into the soil is 6 mg·kg−1).
Table
Table 2. Effects of Cd and Si on Cd and Si concentrations of different fractions of the seedlings.
Table 2. Effects of Cd and Si on Cd and Si concentrations of different fractions of the seedlings.
SpeciesCd
Concentration
(mg kg−1)		Si
Concentration
(mg kg−1)		Si Concentration (mg kg−1)Cd Concentration (mg kg−1)
RootStemLeafRootStemLeaf
Schima superba0Si01.646 ± 0.491c1.253 ± 0.047d1.600 ± 0.174e0.780 ± 0.177f0.127 ± 0.068g
Si14.320 ± 1.290a1.745 ± 0.301bc2.235 ± 0.217bc0.680 ± 0.011f0.530 ± 0.060g
6Si01.336 ± 0.197c1.426 ± 0.150cd1.477 ± 0.165e22.016 ± 0.300e25.920 ± 2.272de0.193 ± 0.035d
Si13.785 ± 0.334a1.855 ± 0.070b2.06 ± 0.139cd22.746 ± 2.41e17.936 ± 2.110f0.113 ± 0.015d
12Si01.900 ± 0.040bc1.153 ± 0.133de1.760 ± 0.131cd28.267 ± 1.164e22.360 ± 2.833de2.720 ± 0.191b
Si13.875 ± 0.544a2.280 ± 0.556a2.800 ± 0.070a20.257 ± 2.415cd17.013 ± 0.455f1.280 ± 0.325c
24Si01.703 ± 0.255a1.026 ± 0.116de1.817 ± 0.104de43.337 ± 3.917ab37.990 ± 6.725b2.810 ± 0.612b
Si13.865 ± 0.256a1.330 ± 0.095d2.500 ± 0.150ab36.923 ± 2.495cde28.283 ± 3.391cd1.623 ± 0.359c
36Si01.520 ± 0.376c0.817 ± 0.030e1.850 ± 0.020de83.793 ± 6.870a62.136 ± 1.995a4.150 ± 0.096a
Si12.680 ± 0.214b1.395 ± 0.098cd2.345 ± 0.463bc60.087 ± 1.581b36.187 ± 0.196bc2.683 ± 0.096b
Chinese sweetgum0Si03.270 ± 0.319c2.650 ± 0.156de3.160 ± 0.987cd0.390 ± 0.007e0.127 ± 0.011f
Si14.333 ± 0.090b4.316 ± 0.280bc4.383 ± 0.198a0.336 ± 0.089e0.186 ± 0.040f
6Si03.793 ± 0.178bc3.703 ± 0.267cd2.703 ± 0.266d3.220 ± 0.588e1.997 ± 0.455ef0.586 ± 0.068d
Si15.660 ± 0.402a4.843 ± 0.491b4.253 ± 0.168ab1.543 ± 0.254e1.683 ± 0.317ef0.323 ± 0.075e
12Si03.363 ± 0.260c2.393 ± 0.345e2.420 ± 0.036d11.670 ± 0.916bc14.903 ± 0.551c1.543 ± 0.196bc
Si15.880 ± 0.186a6.323 ± 0.737c3.520 ± 0.156d8.620 ± 1.202d7.106 ± 0.861de0.556 ± 0.086d
24Si03.756 ± 0.116bc2.453 ± 0.393e2.450 ± 0.446d24.540 ± 0.947a22.816 ± 1.384b2.346 ± 1.743ab
Si16.206 ± 0.065a6.523 ± 0.394a4.443 ± 0.542a16.726 ± 1.677b16.906 ± 0.643c0.956 ± 0.086cde
36Si02.567 ± 0.239d2.790 ± 0.081de2.426 ± 0.392d26.987 ± 2.177a35.243 ± 4.496a3.680 ± 0.535a
Si14.377 ± 0.315b5.246 ± 0.284b2.613 ± 0.342d14.626 ± 0.483bc26.583 ± 3.912b1.766 ± 0.309bc
Chinese
fir		0Si03.260 ± 0.329cd1.453 ± 0.203de1.270 ± 0.295cd0.293 ± 0.090f0.868 ± 0.196f0.480 ± 0.180e
Si13.310 ± 0.255c1.785 ± 0.530cd1.263 ± 0.304cd0.393 ± 0.123f0.268 ± 0.228f0.473 ± 0.215e
6Si02.740 ± 0.217d1.170 ± 0.036e0.933 ± 0.104d16.830 ± 1.518e21.770 ± 0.541e1.257 ± 0.223e
Si14.110 ± 0.518b2.095 ± 0.320bc1.930 ± 0.114a11.220 ± 1.680e16.093 ± 2.138e1.227 ± 0.225e
12Si02.727 ± 0.225d1.607 ± 0.127de1.250 ± 0.158cd68.560 ± 1.647e42.763 ± 2.963d5.176 ± 0.098c
Si13.295 ± 0.150c2.370 ± 0.265ab1.745 ± 0.392ab40.746 ± 7.868d52.013 ± 5.838c4.440 ± 0.343d
24Si03.330 ± 0.276cd1.623 ± 0.127de0.983 ± 0.045d91.263 ± 3.551b51.960 ± 4.869c6.633 ± 0.591b
Si14.765 ± 0.480b2.105 ± 0.293bc1.445 ± 0.112bc42.326 ± 5.028d39.483 ± 1.341d5.600 ± 0.552c
36Si01.817 ± 0.265e1.446 ± 0.416de0.890 ± 0.173d112.650 ± 9.610a99.226 ± 7.930a8.650 ± 1.064a
Si15.760 ± 0.452a2.590 ± 0.112a1.530 ± 0.261bc67.010 ± 8.578c61.263 ± 6.524b5.900 ± 0.230bc
Note: Each value is a mean of six repetitions. Lowercase letters indicate significant differences according to the Turkey’s test (p < 0.05).
Table
Table 3. Effects of Cd and Si on TF values of the seedlings.
Table 3. Effects of Cd and Si on TF values of the seedlings.
SpeciesCd Concentration
(mg kg−1)		Si Concentraion
(mg kg−1)		TF
Root-StemRoot-Leaf
Schima superba0Si00.180 ± 0.118d
Si10.312 ± 0.132cd
6Si01.177 ± 0.111a0.360 ± 0.004a
Si10.800 ± 0.177bc0.351 ± 0.001a
12Si00.791 ± 0.097bc0.154 ± 0.009b
Si10.847 ± 0.096b0.195 ± 0.024b
24Si00.878 ± 0.158b0.030 ± 0.007bc
Si10.764 ± 0.048bc0.014 ± 0.009c
36Si00.753 ± 0.110bc0.008 ± 0.001c
Si10.603 ± 0.012c0.001 ± 0.003c
Chinese sweetgum0Si00.335 ± 0.091f
Si10.559 ± 0.053ef
6Si00.617 ± 0.034ef0.206 ± 0.037a
Si10.592 ± 0.173ef0.213 ± 0.056a
12Si00.768 ± 0.097de0.133 ± 0.022bc
Si10.838 ± 0.134cde0.111 ± 0.009c
24Si00.932 ± 0.090cd0.095 ± 0.069c
Si11.017 ± 0.107cd0.159 ± 0.049abc
36Si01.318 ± 0.244b0.137 ± 0.023bc
Si11.521 ± 0.297b0.210 ± 0.018a
Chinese fir0Si00.335 ± 0.091f1.832 ± 0.982a
Si10.559 ± 0.053ef1.202 ± 0.512b
6Si00.617 ± 0.034ef0.075 ± 0.017c
Si11.099 ± 0.173bc0.110 ± 0.009c
12Si00.767 ± 0.097de0.075 ± 0.001c
Si10.838 ± 0.184cde0.112 ± 0.028c
24Si00.932 ± 0.090cd0.073 ± 0.009c
Si11.017 ± 0.107cd0.134 ± 0.026c
36Si01.317 ± 0.244b0.077 ± 0.104c
Si11.821 ± 0.296a0.088 ± 0.009c
Note: Each value is a mean of six repetitions. Lowercase letters indicate significant differences according to the Turkey’s test (p < 0.05).
Table
Table 4. Effects of Cd and Si on BCF values of the seedlings.
Table 4. Effects of Cd and Si on BCF values of the seedlings.
SpeciesCd
Concentration
(mg kg−1)		Si Concentraion (mg kg−1)BCF
RootStemLeaf
Schima superba0Si01.399 ± 0.387de0.222 ± 0.112e
Si10.968 ± 0.060de0.120 ± 0.009e
6Si03.906 ± 0.067a4.589 ± 0.263a0.034 ± 0.004cd
Si12.839 ± 0.316a3.037 ± 0.422b0.019 ± 0.003e
12Si02.413 ± 0.050a1.908 ± 0.215c0.247 ± 0.012a
Si11.647 ± 0.241de1.008 ± 0.091d0.103 ± 0.024bc
24Si02.954 ± 0.169ab1.724 ± 0.396c0.226 ± 0.022ab
Si11.538 ± 0.072de0.753 ± 0.018de0.067 ± 0.014ab
36Si02.535 ± 0.422b1.879 ± 0.030c0.225 ± 0.004ab
Si11.759 ± 0.065de1.062 ± 0.062d0.098 ± 0.007cd
Chinese sweetgum0Si00.792 ± 0.045d0.362 ± 0.027d
Si11.143 ± 0.236bc0.631 ± 0.077cd
6Si02.507 ± 0.057b1.567 ± 0.743a0.449 ± 0.145a
Si10.658 ± 0.210cd0.720 ± 0.264bcd0.238 ± 0.053b
12Si01.421 ± 0.028bc1.091 ± 0.143abc0.388 ± 0.027a
Si10.923 ± 0.096d0.762 ± 0.091bcd0.103 ± 0.003bc
24Si01.297 ± 0.016bc1.209 ± 0.114a0.222 ± 0.089b
Si10.763 ± 0.044d0.774 ± 0.050bcd0.120 ± 0.029b
36Si01.122 ± 0.254bc1.441 ± 0.185a0.249 ± 0.021b
Si10.407 ± 0.004d0.740 ± 0.116bcd0.085 ± 0.008cd
Chinese fir0Si00.867 ± 0.107e2.651 ± 0.789bc0.358 ± 0.161c
Si11.093 ± 0.842e0.609 ± 0.324e2.360 ± 1.592a
6Si03.260 ± 0.286c4.249 ± 0.646a0.772 ± 0.061cd
Si11.795 ± 0.212d2.591 ± 0.438bcd0.713 ± 0.184bc
12Si06.907 ± 0.238a4.318 ± 0.468bcd1.609 ± 0.141ab
Si13.501 ± 0.795c4.480 ± 0.792a0.796 ± 0.214cd
24Si04.823 ± 0.203b2.164 ± 0.251bc2.256 ± 0.361a
Si11.999 ± 0.317d1.557 ± 0.085d1.074 ± 0.156bc
36Si03.381 ± 0.372c2.979 ± 0.320b1.535 ± 0.008ab
Si11.882 ± 0.261d1.719 ± 0.189d0.813 ± 0.273cd
Note: Each value is a mean of six repetitions. Lowercase letters indicate significant differences according to the Turkey’s test (p < 0.05).
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Wang, Z.; Jin, S.; Su, Y.; He, D.; Wang, Y.; Chen, Y.; Lin, C.; Liao, X.; Zheng, D. Impact of Silica Addition on Alleviating Cadmium Stress: Case Studies of Three Afforestation Tree Species Seedlings in Southern China. Forests 2022, 13, 1641. https://doi.org/10.3390/f13101641

AMA Style

Wang Z, Jin S, Su Y, He D, Wang Y, Chen Y, Lin C, Liao X, Zheng D. Impact of Silica Addition on Alleviating Cadmium Stress: Case Studies of Three Afforestation Tree Species Seedlings in Southern China. Forests. 2022; 13(10):1641. https://doi.org/10.3390/f13101641

Chicago/Turabian Style

Wang, Ziyang, Shaofei Jin, Yi Su, Dongmei He, Yunxiang Wang, Yifei Chen, Chenlei Lin, Xiaoli Liao, and Dexiang Zheng. 2022. "Impact of Silica Addition on Alleviating Cadmium Stress: Case Studies of Three Afforestation Tree Species Seedlings in Southern China" Forests 13, no. 10: 1641. https://doi.org/10.3390/f13101641

APA Style

Wang, Z., Jin, S., Su, Y., He, D., Wang, Y., Chen, Y., Lin, C., Liao, X., & Zheng, D. (2022). Impact of Silica Addition on Alleviating Cadmium Stress: Case Studies of Three Afforestation Tree Species Seedlings in Southern China. Forests, 13(10), 1641. https://doi.org/10.3390/f13101641

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop