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Article

Inhibition of Photosynthesis in Quercus acutissima Seedlings by LaCl3 Through Calcium Signaling Regulation

by
Xiaohang Weng
1,2,3,4,
Hui Li
1,3,*,
Yongbin Zhou
5,*,
Hongbo Wang
6,
Jian Feng
2,4,
Shihe Yu
2,4 and
Ying Zheng
2,4
1
College of Forestry, Shenyang Agricultural University, No.120 Dongling Road, Shenhe District, Shenyang 110866, China
2
Tree Breeding Laboratory, Liaoning Academy of Forest Sciences, No. 12 Yalu River Street, Huanggu District, Shenyang 110032, China
3
Research Station of Liaohe-River Plain Forest Ecosystem, Chinese Forest Ecosystem Research Network (CFERN), Changtu 112500, China
4
Bai Shizǐ Forest Ecosystem National Observation and Research Station, Dandong 118201, China
5
Institute of Modern Agricultural Research, Dalian University, Dalian 116622, China
6
Forest Management Institute, Jilin Provincial Academy of Forestry Sciences, No.3528 Linhe Street, Nanguan District, Changchun 130033, China
*
Authors to whom correspondence should be addressed.
Forests 2025, 16(10), 1553; https://doi.org/10.3390/f16101553
Submission received: 14 August 2025 / Revised: 2 October 2025 / Accepted: 6 October 2025 / Published: 8 October 2025
(This article belongs to the Special Issue Physiological Responses of Woody Plants to Elevated CO2, Drought, and Climate Variations from Local to Global)
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Abstract

Calcium is an essential macronutrient for plant growth and development, and there is an optimal calcium concentration for plant growth. Calcium ion concentration changes create “calcium signals” that regulate plant growth through perception, decoding, transduction, and response processes. However, the mechanisms by which calcium signaling regulates photosynthesis are still not fully understood. In this study, Quercus acutissima seedlings were used to investigate the inhibitory effects of different concentrations of the calcium channel blocker lanthanum chloride (LaCl3) on photosynthesis and the underlying mechanisms. The results show that increasing LaCl3 concentration significantly decreased photosynthetic parameters, photosynthetic pigment contents, and photosynthetic product accumulation. Long-term water use efficiency decreased with increasing LaCl3 concentration, while instantaneous water use efficiency initially increased and then decreased. Structural equation modeling analysis indicated that LaCl3 concentration was significantly positively correlated with leaf calcium concentration in Quercus acutissima seedlings, while it was significantly negatively correlated with stomatal conductance, carotenoids, and soluble sugar content. The study concludes that LaCl3 directly inhibits the photosynthetic physiological processes of Quercus acutissima seedlings by blocking calcium signaling, providing insights into the regulatory mechanisms of calcium signaling in plant photosynthesis and a theoretical basis for the cultivation and application of Quercus acutissima under varying environmental conditions.

1. Introduction

Calcium is an essential macronutrient for normal plant growth [1]. It functions as a structural component, stabilizing the structure of plant cell walls and membranes, reducing cell wall degradation, regulating membrane permeability, and preventing structural and functional damage to the membrane system [2]. Additionally, calcium acts as a “second messenger” involved in calcium signaling transduction, participating in a range of physiological and metabolic processes during plant growth and responding promptly to various stresses, such as modulating the activity of photosynthetic enzymes [3,4]. Under natural conditions, soil calcium exhibits strong spatial heterogeneity, which may limit plant growth [5]. Numerous existing studies have shown that there is an optimal calcium concentration for plant growth [6]. As the calcium concentration increases, plant growth, photosynthesis, and stress resistance all show a trend of first increasing and then decreasing [7]. Both low and high calcium concentrations can inhibit plant growth and development. For example, calcium deficiency can lead to short and underdeveloped roots, low chlorophyll content, and reduced photosynthetic rate in plants [8]. In contrast, excessively high calcium concentrations can cause toxicity in plants, resulting in the closure of leaf stomata, weakened photosynthesis, and consequently affecting plant growth [9]. However, at present, there are few studies on the mechanism of calcium nutrition in regulating the internal physiological processes of plants. Calcium signaling is an important mechanism of intracellular signal transduction [10]. It primarily regulates plant growth, development, and stress adaptation by modulating the changes in intracellular calcium ion concentrations to transmit information [11,12]. The concentration of calcium can control the temporal and spatial distribution of calcium ions or calmodulin, thereby regulating calcium signaling transduction and influencing the process of cell mitosis [13]. Therefore, investigating calcium signaling is of great significance for plants to adapt to different calcium nutrition environments.
Due to the pleiotropic effects, dynamic equilibrium, and passive transport characteristics of calcium in plants [14], the application of exogenous calcium alone can obscure the specific effects of calcium on photosynthesis. Calcium blockers, however, address this issue effectively. Lanthanum chloride (LaCl3) is a commonly used calcium signaling blocker; it is the radius and charge properties of lanthanum ions that enable them to competitively bind to the binding sites of calcium ion channels (such as cyclic nucleotide-gated channels) or transporters on the cell membrane, thereby inhibiting the influx of calcium ions [15]. Previous studies have demonstrated that the application of LaCl3 can effectively suppress the transduction of calcium signals, consequently affecting the physiological processes of plants [16]. Photosynthesis is the fundamental physiological process for plant growth, development, and biomass accumulation [17]. Calcium ion signaling can regulate the opening and closing of stomata, thereby influencing the amount of carbon dioxide entering the leaf [18]. Meanwhile, calcium signaling also modulates the activity of enzymes involved in the photosynthetic electron transport process, which in turn affects the progression of photosynthesis [19]. Exploring the impact of calcium on photosynthesis is of great significance for elucidating the mechanisms of plant adaptation and regulation to the environment. Therefore, by establishing a gradient of LaCl3, it is possible to investigate the dose–effect relationship between the degree of calcium signaling blockage and the photosynthetic characteristics of plants. This approach allows for a more precise study of the role of calcium signaling in plant photosynthesis, free from the interference of other factors, thereby better revealing the regulatory mechanisms and physiological functions of calcium signaling.
Quercus acutissima, a deciduous broad-leaved tree species belonging to the genus Quercus of the family Fagaceae, is drought-resistant and can thrive in poor soils [20]. It also has a strong capacity for soil and water conservation and is one of the main tree species used for afforestation in soil and water conservation forests [21]. In Liaoning Province, it is mainly distributed in the mountainous and hilly areas of southern Liaoning and the Liaodong Peninsula [22]. Quercus acutissima has a high demand for calcium and is highly sensitive to changes in calcium concentration, making it an ideal model tree species for studying calcium signaling mechanisms [23]. Currently, research mainly focuses on the role of calcium in promoting plant growth and the regulatory role of calcium signaling in plant stress responses [24,25,26]. However, the specific mechanisms by which calcium signaling affects photosynthesis in Quercus acutissima seedlings remain unclear. Therefore, this study selects Quercus acutissima as the experimental material and investigates the inhibitory effect of calcium signaling on photosynthesis in Quercus acutissima seedlings and its underlying mechanism through LaCl3 treatment. The following hypotheses are proposed: (1) LaCl3 can regulate the absorption and distribution of calcium ions in various organs of Quercus acutissima. (2) LaCl3 treatment will block calcium signaling, thereby directly inhibiting the photosynthetic physiological processes. Through this study, we hope to elucidate the regulatory mechanisms of calcium signaling in the photosynthesis of Quercus acutissima seedlings and provide a theoretical basis for the cultivation and application of Quercus acutissima under different environmental conditions.

2. Materials and Methods

2.1. Experimental Materials and Treatment Methods

The acorns of Quercus acutissima were subjected to pre-germination treatment in an artificial climate chamber until the radicle length exceeded 2 cm (The parameters are set as follows: the day/night temperatures are 25 and 18 °C, respectively, the relative humidity is 85%, the light intensity during the day is 250 μmol·m−2·s−1, and the photoperiod is 12 h of light and 12 h of darkness.). Subsequently, on 20 May 2017, the seeds were transplanted into plastic pots with an inner diameter of 15 cm, a depth of 12 cm, and a volume of approximately 1 L. The seeds of Quercus acutissima were collected in Fushun City, Liaoning Province, China (125.24° E, 41.9425° N, elevation 673 m), where the mean annual temperature is 5.1 °C and the mean annual precipitation is 863 mm. Seedlings were cultivated in acid-washed quartz sand until developing 2–3 true leaves (about 17 days). Uniform-sized seedlings were selected for hydroponic treatment in controlled laboratory conditions, with the nutrient solution being replaced every 7 days until the seedlings were harvested (the duration of LaCl3 treatment was approximately 60 days). Following the sand culture nutrient solution formula ratio established by Xie et al. [27], dissolve the components in deionized water and adjust the pH of the culture solution to a stable range of 5.0–6.0 using NaOH solution. Calcium is provided by anhydrous CaCl2 at a concentration of 5.0 mmol·L−1. Other compounds providing macronutrients include KNO3, MgSO4·7H2O, NaNO3, KH2PO4, EDTA and FeSO4·7H2O, (Sinopharm Chemical Reagent Co. Ltd., Shanghai, China) ensuring the concentrations of elements N, P, K, Mg, and Fe in the nutrient solution are 97.15, 1, 13.05, 2, and 0.1 mmol·L−1, respectively. The Ca2+ channel blockers use anhydrous lanthanum chloride (LaCl3), with blocking gradients set at 0, 1.5, 3.0, 4.5 and 6.0 mmol·L−1.

2.2. Determination of the Growth Index of Quercus acutissima Seedlings

2.2.1. Biomass Determination of Quercus acutissima Seedlings

During seedling harvesting, three Quercus acutissima seedlings from each treatment were selected in a non-destructive manner in July 2017. Whole plants were removed from the planting pots. After washing, the whole plants were divided into roots, stems, and leaves with pruning shears and placed into envelopes for marking. These envelopes were then placed in an oven at 105 °C until their weights remained constant [28]. The dry weights of the underground biomass, aboveground biomass and total plant biomasses were determined with an analytical balance.

2.2.2. Determination of Photosynthetic Characteristics of Quercus acutissima Seedlings

The photosynthetic and photoresponse characteristic parameters were measured using a photosynthesis instrument: During the peak growth period of Quercus acutissima seedlings (in July 2017), on a sunny morning, the portable photosynthesis measurement system Li-6400 (LI-COR, Inc., Lincoln, NE, USA) was used to measure the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), light response curve of photosynthesis, and other photoresponse characteristic parameters of the leaves of Quercus acutissima seedlings. The effective light radiation intensity (PAR) was controlled at 1000 μmol·m−2·s−1, and each treatment was repeated 3 times [29].
Take 0.1 g of fresh seedling leaves, soaking and extracting with 95% ethanol for 48 h, the absorbance values were measured at wavelengths of 665 nm, 649 nm and 479 nm, and the contents of chlorophyll a, chlorophyll b and carotenoids were calculated [30]. The soluble sugars and starch were determined by the anthrone colorimetric method [31]; the soluble proteins were determined by the Coomassie brilliant blue method [32]. Calculate the content of sugars, starch, and soluble proteins using the following standard curves:
YS = 97.798X + 0.123, R2 = 0.9991
YP = 0.0274X + 0.012, R2 = 0.9971
In the aforementioned formula, YS represents the standard curve for soluble sugars and starch, while YP represents the standard curve for soluble protein.

2.2.3. Determination of Water Use Efficiency of Quercus acutissima Seedlings

In the experiment, δ13C is used to represent the long-term water use efficiency (WUEL) of plants, which is measured by a stable isotope spectrometer. The instantaneous water use efficiency (iWUE) is expressed as the ratio of net photosynthetic rate (Pn) to transpiration rate (Tr) [33].
iWUE = Pn/Tr
WUEL = A/Gs = (Ca − Ci)/1.6 = Ca (1 − Ci/Ca)/1.6 = Ca (b − δ13C)/1.6(b − a)
where A represents the photosynthetic carbon fixation, Gs stands for stomatal conductance, and Ca and Ci are CO2 pressure values in the atmosphere and leaf cells. A and b are the partial effect of CO2 diffusion into stomata and the partial effect of stomatal photosynthetic carboxylase RUBP on carbon isotopes, respectively.

2.2.4. Calcium Element Determinations in Each Quercus acutissima Organ

A 0.1 g plant sample was weighed and mixed with 8 mL of analytical-grade nitric acid and 2 mL of analytical-grade perchloric acid, (Sinopharm Chemical Reagent Co. Ltd., Shanghai, China). The mixture was digested using an electric hot plate (Midea MC-22MB06, Foshan, China). After digestion, the resulting extract was analyzed for calcium concentration using a flame atomic absorption spectrophotometer (AA300, PerkinElmer Inc., Waltham, MA, USA) at a wavelength of 422.7 nm. The instrument was calibrated with a series of calcium standard solutions (1–10 ppm) [34].

2.3. Statistical Analysis

Excel and SPSS 22.0 software were used for sorting and drawing, statistical analysis and difference analysis. GraphPad prism 9.5 was used for drawing charts and fit correlation relationship equations. All experiments were conducted with three replicates, and the results are expressed as the mean ± standard error (SE). The different letters in the chart indicate that the difference in each index between different calcium treatments reached the significance level of 5%.

3. Results

3.1. There Is an Optimal Calcium Concentration for the Growth of Quercus acutissima Seedlings

The biomass accumulation of Quercus acutissima seedlings increases initially and then decreases with the rise in external calcium concentration (Table 1). The underground, aboveground, and total biomass of Quercus acutissima seedlings all reached their maximum values when the external calcium content was 5 mmol·L−1, measuring 1.77 g, 2.18 g, and 3.95 g, respectively, with the root-to-shoot ratio being 27.86%. Compared with the treatment without calcium addition, the increase was significant by 38.28%, 40.65%, and 39.58%, respectively (p < 0.05). With the increase in exogenous calcium concentration, the root to shoot ratio of Quercus acutissima seedlings showed a trend of increasing first, then decreasing, followed by an increase. The root to shoot ratio reached its maximum value at a calcium concentration of 50 mg·kg−1 and its minimum value at a concentration of 400 mg·kg−1. Therefore, optimal exogenous calcium can promote the growth of Quercus acutissima, with a more pronounced promote effect on the aboveground parts than the underground parts of the seedlings. Meanwhile, excessive calcium has a stronger inhibitory effect on the aboveground growth of Quercus acutissima seedlings compared to the underground parts.

3.2. Effect of LaCl3 on the Calcium Concentration in Different Organs of Quercus acutissima Seedlings

When LaCl3 treatment was applied to Quercus acutissima seedlings under optimal calcium concentration (200 mg·kg−1), the water-soluble calcium content in different organs of the seedlings showed significant trends as LaCl3 concentration increased, yet the trends were not uniform (Figure 1). As the LaCl3 concentration increases, the calcium concentration in the leaves of Quercus acutissima seedlings first increases and then decreases, reaching the peaking at 4.5 mmol·L−1 LaCl3, which is 80.41% higher than that in the untreated group and significantly different from other treatments (p < 0.05). In stems, the calcium content first decreases and then increases with rising LaCl3 concentration, reaching the minimum at 1.5 mmol·L−1 LaCl3, which is 10.42% lower than the untreated group and also significantly different from other treatments (p < 0.05). In roots, the calcium content significantly decreases with increasing LaCl3 concentration (p < 0.05).

3.3. Effect of LaCl3 on the Photosynthetic Characteristics of Quercus acutissima Seedlings

3.3.1. Effect of LaCl3 on the Photosynthetic Parameters of Quercus acutissima Seedlings

LaCl3 inhibits the photosynthesis in plants. With the increase in LaCl3 application, the net photosynthetic rate (Pn) (Figure 2A), stomatal conductance (Gs) (Figure 2B), and transpiration rate (Tr) (Figure 2C) in the leaves of Quercus acutissima seedlings showed a downward tendency. The photosynthetic parameters in the LaCl3 treatment were significantly different from those in the control group (p < 0.05). Through linear or nonlinear model fitting, it has been found that the Pn (R2 = 0.95, p < 0.05) significantly and nonlinearly negatively correlated with LaCl3, while Gs (R2 = 0.92, p < 0.01) and Tr (R2 = 0.86, p < 0.05) are highly significantly or significantly and linearly negatively correlated with LaCl3.
After the blockage of Ca2+ ion channels, the photosynthetic rate declined. Under different LaCl3 treatments, the light response curves of Quercus acutissima seedlings showed an initial increase, followed by a gradual stabilization (Figure 3). As shown in the figure, under varying LaCl3 levels, the changes in Pn with increasing photosynthetically active radiation (PAR) followed the same pattern. When PAR was in the range of 0–250 μmol·m−2·s−1, Pn increased rapidly. At 4.5 mmol·L−1 LaCl3 treatment, Pn stabilized once PAR reached 250 μmol·m−2·s−1. Treatments with 1.5, 3.0, and 6.0 mmol·L−1 LaCl3 led to Pn stabilization at PAR 500 μmol·m−2·s−1, whereas the control group (0 mmol·L−1 LaCl3) only stabilized at PAR 750 μmol·m−2·s−1. However, the rates of increase varied among treatments, following the order: 0 > 1.5 > 3.0 > 6.0 > 4.5 mmol·L−1. This indicates that LaCl3 application affected light absorption in Quercus acutissima seedlings, with the degree of photosynthetic capacity reduction rising as the calcium-blocking effect intensified.
Table 2 shows the changes in the photosynthetic response characteristics of Quercus acutissima seedlings under different LaCl3 treatments. With the increase in the concentration of the calcium channel blocker LaCl3, the maximum net photosynthetic rate, apparent quantum efficiency, light saturation point, and dark respiration rate of the seedlings all showed a downward trend, reaching their minimum values at a LaCl3 concentration of 4.5 mmol·L−1. Specifically, compared to the control group (0 mmol·L−1 LaCl3), these parameters decreased by 89.00%, 64.79%, 39.54%, and 45.48%, respectively. However, at a LaCl3 concentration of 6.0 mmol·L−1, the maximum net photosynthetic rate, apparent quantum efficiency, light saturation point, and dark respiration rate exhibited slight increases. In contrast, the light compensation point increased after the application of LaCl3, peaking at a LaCl3 concentration of 4.5 mmol·L−1, with an increase of 21.16 μmol·m−2·s−1 compared to the control group. Nevertheless, it decreased slightly at a LaCl3 concentration of 6.0 mmol·L−1.

3.3.2. Effect of LaCl3 on the Photosynthetic Pigments’ Accumulation in Quercus acutissima Seedlings

LaCl3 inhibits the accumulation of photosynthetic pigments in plants. With the increase in LaCl3 application, the chlorophyll a (Figure 4A), chlorophyll b (Figure 4B), chlorophyll (a + b) (Figure 4C), and carotenoid concentrations (Figure 4D) in the leaves of Quercus acutissima seedlings showed a downward tendency. The photosynthetic pigment accumulation in the LaCl3 treatment was significantly different from that in the control group (p < 0.05). The results of the logistic growth model fitting indicated that chlorophyll a (R2 = 0.93) and carotenoid (R2 = 0.90) levels were significantly negatively correlated with LaCl3 concentration (p < 0.05). Although chlorophyll b (R2 = 0.85) and total chlorophyll (a + b) (R2 = 0.92) levels also decreased with increasing LaCl3 concentration, these relationships did not reach statistical significance (p > 0.05).

3.3.3. LaCl3 Inhibits the Accumulation of Photosynthate in the Leaves of Quercus acumosa Seedlings

LaCl3 inhibits the accumulation of photosynthate in plants. With the increase in LaCl3 application, the soluble sugar (Figure 5A), starch (Figure 5B), unstructured carbohydrates (Figure 5C), and soluble protein (Figure 5D) in the leaves of Quercus acutissima seedlings showed a downward tendency. The photosynthate accumulation in the LaCl3 treatment was significantly different from that in the control group (p < 0.05). The results of the linear fitting indicated that soluble sugar (R2 = 0.87), starch (R2 = 0.77), and unstructured carbohydrates (R2 = 0.85) levels were significantly negatively correlated with LaCl3 concentration (p < 0.05). And soluble protein (R2 = 0.96) levels were extremely significantly negatively correlated with LaCl3 concentration (p < 0.001).

3.4. Effect of LaCl3 on the Water Use Efficiency of Quercus acutissima Seedlings

Using δ13C to characterize long-term water use efficiency (WUEL) in leaves tissues of Quercus acutissima seedlings. With increasing concentrations of exogenous LaCl3, the δ13C of Quercus acutissima seedlings progressively decreased, reaching its minimum value at 6 mmol·L−1 LaCl3 (Figure 6). At this concentration, it was significantly reduced by 0.44 compared to the without LaCl3 control, with statistically significant differences observed across all other treatments (p < 0.05). This means that the addition of calcium-blocking agents will significantly inhibit the WUEL of the leaves of Quercus acutissima seedlings. While the instantaneous water use efficiency (iWUE) initially increased then declined, peaking at intermediate LaCl3 concentrations (Figure 6). When the concentration of LaCl3 was 3.0 mmol·L−1, its iWUE reached its maximum value of 5.81, which was 1.37 higher than that without LaCl3. And the differences from other treatments reached a significant level (except for the case where the LaCl3 concentration was 1.5 mmol·L−1) (p < 0.05).

3.5. The Response Mechanism of Photosynthesis in Quercus acutissima Seedlings to LaCl3

The structural equation model (SEM) was employed to quantify the complex relationships between LaCl3 concentration and the calcium concentration in the leaves of young Quercus acutissima seedlings, as well as carotenoid, stomatal conductance, and soluble sugar content (Figure 7). The resulting SEM had a chi-square value (χ2) of 0.47 with 1 degree of freedom (df). The overall model fit was extremely strong, with a Goodness of Fit Index (GFI) of 0.999 and a Root Mean Square Error of Approximation (RMSEA) of less than 0.001. These results indicate that all important relationships were specified in the model, and the model fit the data very well, making it acceptable. The R2 value reflects the explanatory power of the independent variables for the dependent variable. In this model, the R2 for soluble sugar is the highest, reaching 0.948, indicating that the model has a very strong ability to explain its variability. The explanatory power for the other variables decreases in the following order: stomatal conductance (0.932), carotenoids (0.835), and leaf calcium concentration (0.795). The model indicates that there is a significant positive correlation between LaCl3 concentration and the calcium concentration in the leaves of young Quercus acutissima seedlings, while there are significant negative correlations between LaCl3 concentration and stomatal conductance, carotenoids, and soluble sugar content. However, there are no significant correlations between leaf calcium concentration and stomatal conductance, carotenoids, or soluble sugar content. Therefore, lanthanum chloride can directly negatively regulate the photosynthetic capacity of young Quercus acutissima seedlings.

4. Discussion

4.1. LaCl3 Affects Calcium Ion Absorption and Distribution in Quercus acutissima Seedlings

Calcium is an important structural substance and regulatory substance in the growth and development of plants, while calcium signaling is responsible for responding to various stresses in plants [35]. Calcium deficiency inhibits the activity of photosystem II, reducing the efficiency of light energy conversion, while calcium excess leads to stomatal closure, decreasing CO2 uptake and thus lowering the rate of photosynthesis in plants [5]. When the external environment changes, calcium signaling regulates calcium ion channels to maintain the transport and storage of calcium ions within the cell [36]. LaCl3, as a calcium signaling inhibitor, primarily blocks calcium signaling in plants by competitively binding to the binding sites of calcium ion channels or transporters [37]. In this study, with the increase in the concentration of LaCl3, the calcium ion concentration in the leaves initially increased and then decreased (but the calcium concentration in the leaves with LaCl3 application was higher than the control in all cases), while that in stems first decreased and then increased. In contrast, the calcium ion concentration in roots significantly decreased (Figure 1). These results indicate that LaCl3 can regulate the distribution of calcium ions within the plant, thereby supporting hypothesis (1). The same conclusion was also reached in the study of Mesembryanthemum crystallinum [38]. For Quercus acutissima seedlings, low La3+ concentrations bind to cell membrane phospholipids and proteins, temporarily increasing permeability and facilitating Ca2+ uptake [39]. However, higher La3+ concentrations can block calcium channels, reducing Ca2+ levels. Despite this, initial promotion and stress responses may keep Ca2+ levels higher than controls [40]. Secondly, the transport of calcium within plants mainly relies on the transpiration of xylem [41], while LaCl3 interferes with the passive transport of calcium ions in the xylem, resulting in reduced accumulation of calcium ions in stems and roots [42]. While La3+ severely damages the membrane system, causing Ca2+ inside the stem cells to leak out and abnormally accumulate in the apoplast space. As a result, the calcium ion concentration in the stems was significantly higher than that in the control when the concentration of lanthanum chloride was 4.5 and 6 mmol·L−1 [43]. Therefore, this study preliminarily clarifies that LaCl3 can dynamically regulate the distribution of calcium ions in different plant organs by interfering with their transmembrane transport and vascular conduction. This finding highlights the critical role of calcium signaling in coordinating ion homeostasis within plants.

4.2. The Inhibitory Effect of LaCl3 on Photosynthesis and Its Mechanism

Photosynthesis is the process by which plants absorb light energy to convert carbon dioxide and water into organic matter while releasing oxygen [44]. It provides the energy and organic material basis for plant growth and is the core physiological process of plant growth and development [45]. The results of this study indicate that with the increase in LaCl3 concentration, the photosynthetic parameters of young Quercus acutissima seedlings (including net photosynthetic rate, stomatal conductance, and transpiration rate), the content of photosynthetic pigments (the chlorophyll a, chlorophyll b, chlorophyll (a + b), and carotenoid concentrations), and the accumulation of photosynthetic products (the soluble sugar and starch) all decreased (Figure 2, Figure 4 and Figure 5). Moreover, there was a significant negative linear or nonlinear correlation between these parameters and the LaCl3 concentration. These results indicate that LaCl3 treatment will block calcium signaling, thereby directly inhibiting the photosynthetic physiological processes., thereby supporting hypothesis (2). The reasons are as follows: On the one hand, after LaCl3 blocks the calcium signaling, the stomatal conductance decreases, resulting in reduced CO2 entering the leaves, thereby inhibiting photosynthesis [46]. On the other hand, LaCl3 treatment alters the distribution of calcium ions, affecting the structure and function of membranes, and simultaneously inhibiting the accumulation of starch, which in turn suppresses photosynthesis [47]. Experts and scholars have demonstrated in their research on Mulberry seedlings [48], Salvia miltiorrhiza seedlings [49], and Corn [50] that when the concentration of LaCl3 is between 20 and 60 mg·L−1, it can promote photosynthesis in plants. However, when the concentration of LaCl3 is too high, the photosynthetic performance of plants (including stomatal conductance, quantum efficiency, and chlorophyll content) will be significantly inhibited. Compared with the above results, in this experiment, the application of exogenous LaCl3 did not promote the photosynthesis of Quercus acutissima seedlings, which may be due to the excessively high concentration of LaCl3 added in this experiment. The effects of LaCl3 on the long-term water use efficiency (WUEL) and instantaneous water use efficiency (iWUE) of Quercus acutissima seedlings in this study also confirmed this result. With the increase in LaCl3 concentration, WUEL gradually decreased, while iWUE first increased and then decreased, reaching a peak at the medium concentration. The effects of LaCl3 on the WUEL and iWUE of Quercus acutissima seedlings in this study also confirmed this result. With the increase in LaCl3 concentration, WUEL gradually decreased, while iWUE first increased and then decreased, reaching a peak at the medium concentration [51]. The results of this study also revealed that lanthanum chloride can directly increase the calcium concentration in leaves. However, there was no significant correlation between calcium concentration and stomatal conductance, carotenoids, or soluble sugar content. This is likely because lanthanum chloride interacts with key components such as calcium ion channels and calcium sensors on the plant cell membrane, disrupting the normal transmission of calcium signals. This disruption affects the expression of photosynthesis-related genes and the activity of photosynthetic enzymes, thereby significantly impacting the plant’s photosynthetic capacity. In contrast, leaf calcium concentration is merely a result of calcium signal transduction, reflecting the steady-state level of intracellular calcium ions rather than the dynamic transmission process of calcium signals [52]. The regulation of photosynthesis relies on the rapid and precise transmission of calcium signals and the subsequent intracellular signal cascade reactions. Simple changes in calcium concentration alone cannot directly trigger these complex regulatory mechanisms, and thus cannot significantly regulate photosynthesis. This discovery provides preliminary evidence for the role of calcium signaling in the regulation of plant photosynthesis and lays an important foundation for further in-depth investigations.

4.3. Limitations and Future Work

To conclude, our study highlights the critical role of LaCl3 in regulating the photosynthesis of Quercus acutissima seedlings and offers valuable insights into the potential mechanisms through which LaCl3 influences photosynthetic processes. That said, we recognize that our work has certain inherent limitations—common considerations in exploratory research—that provide meaningful directions for further refinement in future investigations. Firstly, the number of biological replicates per treatment group was relatively modest (n = 3). While this sample size was sufficient to detect statistically significant patterns in our analyses, a larger replicate set would further strengthen the generalizability of our findings and help mitigate the potential for Type I and Type II errors [53], ultimately yielding more robust and broadly applicable data. Secondly, we utilized LaCl3 as a non-specific calcium channel blocker, a methodological approach that carries certain unavoidable constraints. For example, LaCl3 may exhibit toxicity at higher concentrations, which could potentially induce unintended stress-related responses beyond the targeted disruption of calcium signaling pathways. To address this, future studies could incorporate more direct measurements of calcium signaling cascades (e.g., real-time monitoring of cytosolic Ca2+ dynamics) to validate and elaborate on the mechanisms we propose. Despite these considerations, our results remain valuable: they provide important theoretical support and practical guidance for advancing scientific forest management, tree species selection and breeding, ecological restoration, and the enhancement of ecosystem service functions. Moving forward, we aim to build on this foundation by exploring these areas further, with the goal of developing a more comprehensive understanding of how calcium signaling regulates plant photosynthesis.

5. Conclusions

In summary, this study investigated the inhibitory effects of different concentrations of the calcium channel blocker LaCl3 on the photosynthesis of Quercus acutissima seedlings and its response intensity. In summary, LaCl3 directly affects the absorption and distribution of calcium ions in Quercus acutissima seedlings by modulating calcium signal transduction. And it indirectly inhibits photosynthesis by regulating key components of the process, including photosynthetic parameters, products, and pigment content. This conclusion enhances our understanding of the underlying mechanisms through which LaCl3 impacts plant photosynthesis and lays theoretical groundwork for future studies on the role of calcium signaling in this process. Furthermore, it offers significant theoretical insights into the cultivation and application of Quercus acutissima across various environmental conditions, thereby supporting the sustainable advancement of scientific forest management and ecological restoration efforts.

Author Contributions

Conceptualization, H.L. and Y.Z. (Yongbin Zhou); methodology, X.W.; validation, X.W.; formal analysis, X.W.; investigation, X.W.; writing—original draft preparation, X.W.; writing—review and editing, H.W., J.F., S.Y., and Y.Z. (Ying Zheng); visualization, X.W.; supervision, H.L. and Y.Z. (Yongbin Zhou); funding acquisition, H.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (31700552, 41450007, 31800364, and 31400611) and the Doctoral Research Start-up Fund (880416020).

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Water-soluble calcium concentration in leaves (A), stems (B) and roots (C) of Quercus acutissima seedlings under various LaCl3 treatments. Each column shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05).
Figure 1. Water-soluble calcium concentration in leaves (A), stems (B) and roots (C) of Quercus acutissima seedlings under various LaCl3 treatments. Each column shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05).
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Figure 2. The photosynthetic parameters of Quercus acutissima seedlings under various LaCl3 treatments. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05). The red line represents the trend line obtained by linear or nonlinear fitting the data, with a 95% confidence interval.
Figure 2. The photosynthetic parameters of Quercus acutissima seedlings under various LaCl3 treatments. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05). The red line represents the trend line obtained by linear or nonlinear fitting the data, with a 95% confidence interval.
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Figure 3. Effect of Lanthanum Chloride (LaCl3) Treatments on the Light Response Curve of Photosynthesis in Quercus acutissima Seedlings.
Figure 3. Effect of Lanthanum Chloride (LaCl3) Treatments on the Light Response Curve of Photosynthesis in Quercus acutissima Seedlings.
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Figure 4. The accumulation of Chlorophyll-a (A), Chlorophyll-b (B), Chlorophyll-a+b (C), and Carotenoid (D) of Quercus acutissima seedlings under various LaCl3 treatments. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05). The red curve represents the trend line obtained by fitting the data to a Logistic growth model, with a 95% confidence interval.
Figure 4. The accumulation of Chlorophyll-a (A), Chlorophyll-b (B), Chlorophyll-a+b (C), and Carotenoid (D) of Quercus acutissima seedlings under various LaCl3 treatments. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05). The red curve represents the trend line obtained by fitting the data to a Logistic growth model, with a 95% confidence interval.
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Figure 5. The accumulation of soluble sugar (A), starch (B), unstructured carbohydrates (C), and soluble protein (D) of Quercus acutissima seedlings under various LaCl3 treatments. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05). The red line represents the trend line obtained by linear fitting the data, with a 95% confidence interval.
Figure 5. The accumulation of soluble sugar (A), starch (B), unstructured carbohydrates (C), and soluble protein (D) of Quercus acutissima seedlings under various LaCl3 treatments. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05). The red line represents the trend line obtained by linear fitting the data, with a 95% confidence interval.
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Figure 6. The water use efficiency of Quercus acutissima seedlings under blocking calcium treatment. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05).
Figure 6. The water use efficiency of Quercus acutissima seedlings under blocking calcium treatment. Each data point shows the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05).
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Figure 7. The effect of LaCl3 on the photosynthetic capacity of Quercus acutissima seedlings leaves. Rectangles represent observed variables. Red and blue solid arrows indicate significant positive and negative relationships, respectively (p < 0.05), while gray dashed arrows indicate non-significant paths (p > 0.05). The numbers on the arrows are the standardized path coefficients, and the width of the arrows represents the strength of the path coefficients. The significance of the paths is denoted by asterisks, where * indicates p < 0.05, ** indicates p < 0.01, *** indicates p < 0.001, and ns indicates p > 0.05.
Figure 7. The effect of LaCl3 on the photosynthetic capacity of Quercus acutissima seedlings leaves. Rectangles represent observed variables. Red and blue solid arrows indicate significant positive and negative relationships, respectively (p < 0.05), while gray dashed arrows indicate non-significant paths (p > 0.05). The numbers on the arrows are the standardized path coefficients, and the width of the arrows represents the strength of the path coefficients. The significance of the paths is denoted by asterisks, where * indicates p < 0.05, ** indicates p < 0.01, *** indicates p < 0.001, and ns indicates p > 0.05.
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Table 1. The biomass of Quercus acutissima seedlings under different calcium treatment.
Table 1. The biomass of Quercus acutissima seedlings under different calcium treatment.
Ca2+ Concentration (mmol·L−1)Underground Biomass (g)Aboveground Biomass (g)Total Biomass (g)Root-Shoot Ratio (%)
01.28 ± 0.054 c1.55 ± 0.048 bc2.83 ± 0.118 d31.50 ± 2.33 ab
1.251.52 ± 0.074 b1.61 ± 0.07 bc3.13 ± 0.103 cd33.87 ± 0.57 a
2.51.72 ± 0.202 a1.69 ± 0.050 b3.42 ± 0.075 bc32.39 ± 2.05 ab
51.77 ± 0.176 a2.18 ± 0.114 a3.95 ± 0.218 a27.86 ± 1.35 b
101.57 ± 0.054 b2.06 ± 0.095 a3.63 ± 0.075 ab27.41 ± 1.34 b
151.54 ± 0.187 b1.76 ± 0.062 b3.30 ± 0.131 c29.49 ± 0.94 b
201.47 ± 0.147 b1.41 ± 0.081 c2.87 ± 0.128 d32.62 ± 2.73 ab
Note: Each digital show the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between of Ca2+ treatments (p < 0.05).
Table 2. Photoresponse characteristic parameters of Quercus acutissima seedlings under different calcium treatments.
Table 2. Photoresponse characteristic parameters of Quercus acutissima seedlings under different calcium treatments.
LaCl3
(mmol·L−1)		Apparent Carboxylation Efficiency (mol·mol−1)Maximum Net Photosynthetic Rate (μmol·m−2·s−1)CO2 Saturation Point (μmol·mol−1)CO2 Compensation Point (μmol·mol−1)Dark Breathing Rate (μmol·m−2·s−1)
00.0209 a9.88 a1903.39 a74.81 c1.46 a
1.50.0147 b8.03 a1873.17 a99.29 c1.37 b
3.00.0100 b4.83 b1746.44 ab145.14 b1.31 b
4.50.0034 c1.87 c1741.46 ab364.63 a1.12 c
6.00.0082 c4.22 b1586.63 b157.38 b1.19 c
Note: Each digital show the mean ± SE value, n = 3. Different lowercase letters indicate significant differences between LaCl3 treatments (p < 0.05).
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Weng, X.; Li, H.; Zhou, Y.; Wang, H.; Feng, J.; Yu, S.; Zheng, Y. Inhibition of Photosynthesis in Quercus acutissima Seedlings by LaCl3 Through Calcium Signaling Regulation. Forests 2025, 16, 1553. https://doi.org/10.3390/f16101553

AMA Style

Weng X, Li H, Zhou Y, Wang H, Feng J, Yu S, Zheng Y. Inhibition of Photosynthesis in Quercus acutissima Seedlings by LaCl3 Through Calcium Signaling Regulation. Forests. 2025; 16(10):1553. https://doi.org/10.3390/f16101553

Chicago/Turabian Style

Weng, Xiaohang, Hui Li, Yongbin Zhou, Hongbo Wang, Jian Feng, Shihe Yu, and Ying Zheng. 2025. "Inhibition of Photosynthesis in Quercus acutissima Seedlings by LaCl3 Through Calcium Signaling Regulation" Forests 16, no. 10: 1553. https://doi.org/10.3390/f16101553

APA Style

Weng, X., Li, H., Zhou, Y., Wang, H., Feng, J., Yu, S., & Zheng, Y. (2025). Inhibition of Photosynthesis in Quercus acutissima Seedlings by LaCl3 Through Calcium Signaling Regulation. Forests, 16(10), 1553. https://doi.org/10.3390/f16101553

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