Abstract
To determine the effects of carboxymethyl chitosan on plant growth and nutrient uptake, Prunus davidiana seedlings were treated with various concentrations of carboxymethyl chitosan. The biomass, physiological characteristics, and nutrient uptake of the treated P. davidiana seedlings were then examined. Compared with the control seedlings, the carboxymethyl chitosan-treated seedlings had a higher biomass and a greater abundance of photosynthetic pigments (i.e., chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), with the best concentration as 2 g/L carboxymethyl chitosan, which increased the shoot biomass and total chlorophyll content by 26.75% and 24.64%, respectively. Moreover, the application of carboxymethyl chitosan enhanced superoxide dismutase and catalase activities, increased the soluble protein content, and decreased the malondialdehyde and proline contents of the P. davidiana seedlings to some extent. Additionally, the carboxymethyl chitosan treatments decreased the total nitrogen content, but increased the total phosphorus and potassium contents in P. davidiana seedlings to some extent. The minimum of total nitrogen content and the maximum of total phosphorus and potassium contents in shoots of P. davidiana seedlings were the concentration of 2 g/L carboxymethyl chitosan, which was decreased by 12.96% and increased by 15.45% and 22.53%, respectively, compared with the control. Therefore, the application of a carboxymethyl chitosan solution may promote the growth, enhance the stress resistance, and alter the nutrient uptake of P. davidiana seedlings, especially at 2 g/L carboxymethyl chitosan.
Keywords: Carboxymethyl chitosan, Prunus davidiana, Growth, Nutrient uptake
Introduction
Chitosan is a deacetylated derivative of chitin (Park and Kim 2010). Chitin, which is widely distributed in shrimp, crab, and insect exoskeletons as well as in algal and fungal cell walls, is an abundant natural polymer with an annual output second only to cellulose (Feng et al. 2018). The cost of converting chitin to chitosan is relatively low. Moreover, chitosan is biodegradable, non-toxic, and has antibacterial properties, and has been widely used in medicines, food, cosmetics (Ma et al. 2017). Regarding its agricultural applications, chitosan is often used as a food preservative and for preventing and controlling plant diseases (Hu et al. 2018). In addition, chitosan also has good film-forming properties, which is relevant for decreasing fruit water loss due to evaporation (Lu 2008). Therefore, chitosan may be useful for agricultural production.
Chitosan has recently been used to promote plant growth and improve crop yield and quality (Guan et al. 2009). A previous study revealed that the application of deacetylation chitosan can promote the growth of coffee plants (Van et al. 2013). Regarding vegetables, water-soluble carboxymethyl chitosan reportedly promotes the growth of cucumber seedlings by increasing their biomass (Yu et al. 2003). Semisynthetic chitosan derivatives (N-succinyl and N, O-dicarboxymethylated) can also induce plant antioxidant defense systems and enhance the antioxidant enzyme activity in plants (Rabêlo et al. 2019). For apple seedlings growing under drought conditions, the application of deacetylation chitosan increases the chlorophyll content, promotes the accumulation of osmotic adjusters (e.g., free amino acids, soluble sugars, and proline), and enhances the activity of protective enzymes (Yang et al. 2009). Thus, treating plants with chitosan may be a viable option for promoting growth and enhancing stress resistance.
Prunus davidiana is a small deciduous tree or shrub belonging to the family Rosaceae (Liu et al. 2017). Additionally, P. davidiana is drought tolerant and cold resistant, making it an excellent rootstock for the grafting of peaches, plums, apricots, and other fruit tree species (Zhang et al. 2019). In the current study, the leaves of P. davidiana seedlings were treated with various chitosan concentrations to promote growth. The effects of the chitosan treatments on P. davidiana seedling growth and nutrient uptake were examined, and the resulting data may be relevant for improving the production of fruit trees.
Materials and methods
Materials
Prunus davidiana seeds were purchased from a market in Chengdu, Sichuan, China.
Non-polluted soil was collected from the Chengdu campus of Sichuan Agricultural University (30° 42′ N, 103° 51′ E) in Chengdu, Sichuan, China. The basic soil properties were as follows: pH, 7.71; organic matter content, 15.29 g/kg; alkaline nitrogen content, 87.99 mg/kg; available phosphorus content, 55.77 mg/kg; and available potassium content, 41.96 mg/kg.
The chitosan is carboxymethyl chitosan (water soluble), with 90% degree of de-acetylation and 80% degree of substitution. The carboxymethyl chitosan was purchased from a chemical market in Chengdu, Sichuan, China.
Experimental design
Experiments were conducted in a greenhouse at the Chengdu campus of Sichuan Agricultural University from April to July 2019. In April 2019, in order to do not damage the roots of seedlings when transplanting, P. davidiana seeds were sown in perlite and irrigated with Hoagland nutrient solution every 3 days until the seedlings reached a height of 10 cm (with about seven true leaves). Four uniformly growing seedlings were transplanted to a pot [15 cm (height) × 18 cm (diameter)] containing 3 kg soil. The soil moisture content was maintained at 80% of field capacity. At 7 days after transplanting, the leaves and stems of P. davidiana seedlings were sprayed with carboxymethyl chitosan solutions (0, 1, 2, 4, or 6 g/L) until water droplets formed on the foliar surface, without dripping. Each treatment was repeated three times.
At 1 month after the carboxymethyl chitosan treatments, mature leaves (9–10 leaves from the top) were collected to measure the photosynthetic pigment content (chlorophyll a, chlorophyll b, carotenoid, and total chlorophyll), the activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT), the soluble protein content, and the malondialdehyde (MDA) content. For the photosynthetic pigment content, leaf samples (0.2 g) cut into pieces were soaked in a 20 mL mixed solution of ethanol and acetone (1:1, v/v) in the dark for 24 h, and then the absorbance at 663, 645, 470, and 652 nm were measured for chlorophyll a, chlorophyll b, carotenoids and total chlorophyll according to Hao et al. (2004). For other items, fresh leaf tissue (1.0 g) was homogenized in 6 mL extraction buffer (0.05 M potassium phosphate buffer [pH 7.0] containing 1 mM EDTA) to extract the enzyme at 4 °C. The homogenate was centrifuged at 11,000×g for 20 min and the supernatant was stored in separate aliquots at − 80 °C to be used for analysis of SOD and CAT activities, and soluble protein and MDA contents, in accordance with the methods of Hao et al. (2004). Additionally, the roots, stem, and leaves of each plant were separately harvested, washed with tap water, and rinsed three times with deionized water. The plant materials were blanched at 110 °C for 15 min, dried at 75 °C until reaching a constant weight, and weighed. The dried tissue samples were finely ground for a subsequent chemical analysis. The proline content used the ethanol extraction and ninhydrin colorimetry to determine as described by Hao et al. (2004). Dried plant samples (1.0 g) were digested in 6 mL H2SO4/H2O2 (5:1, v/v) solution with the electric heating plate at 200 °C until the solution was transparent, and the solution were used to determine the total nitrogen content by the Kjeldahl method, total phosphorus content by the Mo–Sb anti-colorimetry, and total potassium content by the flame photometry according to Bao (2000). The soil in pots were air-dried and ground into a powder (soil particle diameter < 1 mm) to determine the soil pH and quantify the available nutrients. The soil pH was measured with a 1:2.5 (w/v) suspension of soil and deionized water (Bao 2000). The soil alkaline nitrogen content was determined with the alkaline hydrolysis pervasion method, whereas the available phosphorus was extracted from the soil with NaHCO3 and quantified according to Mo–Sb anti-colorimetry. The available potassium content was determined by atomic absorption spectrophotometry (Bao 2000).
Statistical analyses
Data underwent a one-way analysis of variance with the least significant difference at the 5% confidence level. Statistical analyses were conducted with the SPSS 17.0 statistical software (IBM Inc., Chicago, IL, USA).
Results
Biomass of P. davidiana seedlings
The P. davidiana seedling root, stem, leaf, and shoot biomasses increased with increasing carboxymethyl chitosan concentrations up to 2 g/L, but decreased with further increases in the carboxymethyl chitosan concentration (Table 1). At carboxymethyl chitosan concentrations of 1, 2, and 4 g/L, the root biomass significantly increased (p < 0.05) by 25.88%, 54.90%, and 34.12%, respectively, compared with the root biomass of the control seedlings, whereas the shoot biomass significantly increased (p < 0.05) by 10.08%, 26.75%, and 14.81%, respectively, compared with the shoot biomass of the control seedlings. However, the root and shoot biomasses of the seedlings treated with 6 g/L carboxymethyl chitosan were not significantly (p > 0.05) different from the corresponding biomasses of the control seedlings. Additionally, compared with the control seedlings, the P. davidiana seedlings treated with 1, 2, or 4 g/L carboxymethyl chitosan had a higher root/shoot ratio. In contrast, there was no significant difference (p > 0.05) in the root/shoot ratio between the control seedlings and the seedlings treated with 6 g/L carboxymethyl chitosan (Table 1).
Table 1.
Biomass of P. davidiana seedlings
| Treatments (g/L) | Roots (g/plant) | Stems (g/plant) | Leaves (g/plant) | Shoots (g/plant) | Root/shoot ratio |
|---|---|---|---|---|---|
| 0 | 0.255 ± 0.009c | 0.417 ± 0.019c | 0.555 ± 0.018c | 0.972 ± 0.035c | 0.262c |
| 1 | 0.321 ± 0.014b | 0.464 ± 0.011b | 0.606 ± 0.022b | 1.070 ± 0.024b | 0.300ab |
| 2 | 0.395 ± 0.016a | 0.526 ± 0.021a | 0.706 ± 0.013a | 1.232 ± 0.014a | 0.321a |
| 4 | 0.342 ± 0.008b | 0.483 ± 0.016b | 0.633 ± 0.020b | 1.116 ± 0.035b | 0.306a |
| 6 | 0.272 ± 0.011c | 0.424 ± 0.014c | 0.563 ± 0.017c | 0.987 ± 0.021c | 0.275bc |
Values are means (± SE) of 3 replicate pots. Significant differences (indicated by different lowercase letters) within a column are based on a one-way analysis of variance with least significant difference (LSD) (p < 0.05)
Photosynthetic pigment content in P. davidiana seedlings
The chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents in P. davidiana seedlings increased with increasing carboxymethyl chitosan concentrations up to 2 g/L, but decreased when the carboxymethyl chitosan concentration exceeded 2 g/L (Table 2). At carboxymethyl chitosan concentrations of 1, 2, 4, and 6 g/L, the chlorophyll a, total chlorophyll, and carotenoid contents were greater in the carboxymethyl chitosan-treated P. davidiana seedlings than in the control seedlings. The chlorophyll b content in P. davidiana seedlings increased at carboxymethyl chitosan concentrations of 1, 2, and 4 g/L relative to the control level, but not at a carboxymethyl chitosan concentration of 6 g/L. The chlorophyll a/b ratio for seedlings treated with 1 or 2 g/L carboxymethyl chitosan was lower than that of the control seedlings, but the ratio for seedlings treated with 6 g/L carboxymethyl chitosan was higher than that of the control (Table 2). There was no significant difference (p > 0.05) in the chlorophyll a/b ratio between the seedlings treated with 4 g/L carboxymethyl chitosan and the control seedlings.
Table 2.
Photosynthetic pigment content in P. davidiana seedlings
| Treatments (g/L) | Chlorophyll a (mg/g) | Chlorophyll b (mg/g) | Carotenoid (mg/g) | Total chlorophyll (mg/g) | Chlorophyll a/b |
|---|---|---|---|---|---|
| 0 | 2.132 ± 0.052d | 0.628 ± 0.015d | 0.576 ± 0.009c | 2.760 ± 0.066d | 3.393 ± 0.029b |
| 1 | 2.342 ± 0.032b | 0.765 ± 0.012b | 0.628 ± 0.010ab | 3.107 ± 0.025b | 3.061 ± 0.080c |
| 2 | 2.529 ± 0.011a | 0.910 ± 0.026a | 0.640 ± 0.013a | 3.440 ± 0.036a | 2.778 ± 0.068d |
| 4 | 2.345 ± 0.039b | 0.702 ± 0.014c | 0.635 ± 0.020ab | 3.047 ± 0.036b | 3.339 ± 0.101b |
| 6 | 2.275 ± 0.021c | 0.640 ± 0.010d | 0.611 ± 0.016b | 2.915 ± 0.022c | 3.558 ± 0.070a |
Values are means (± SE) of 3 replicate pots. Significant differences (indicated by different lowercase letters) within a column are based on a one-way analysis of variance with least significant difference (LSD) (p < 0.05)
Antioxidant enzyme activity and osmotic adjuster content of P. davidiana seedlings
The application of carboxymethyl chitosan increased the SOD activity, CAT activity, and soluble protein content of P. davidiana seedlings relative to the control levels (Table 3). The CAT activity and soluble protein content peaked at 2 g/L carboxymethyl chitosan. The 1, 2, and 4 g/L carboxymethyl chitosan treatments decreased the MDA and proline contents of P. davidiana seedlings relative to the control levels, whereas the exposure to 6 g/L carboxymethyl chitosan increased or had no significant (p > 0.05) effect on the MDA and proline contents relative to the control levels.
Table 3.
Antioxidant enzyme activity and osmotic adjuster content of P. davidiana seedlings
| Treatments (g/L) | SOD activity (U/g FW) | CAT activity (mg/g/min FW) | Soluble protein content (mg/g) | MDA content (μmol/kg) | Proline content (μg/g) |
|---|---|---|---|---|---|
| 0 | 349.4 ± 8.55d | 0.639 ± 0.016d | 20.01 ± 0.65d | 30.70 ± 1.29b | 411.3 ± 14.66a |
| 1 | 410.8 ± 11.32b | 0.904 ± 0.010b | 22.00 ± 0.72c | 27.08 ± 0.89c | 274.6 ± 8.81b |
| 2 | 469.8 ± 13.36a | 1.105 ± 0.027a | 30.60 ± 0.88a | 23.79 ± 1.01d | 227.4 ± 10.94c |
| 4 | 461.0 ± 9.36a | 0.941 ± 0.031b | 25.50 ± 0.48b | 22.77 ± 1.09d | 249.0 ± 15.75c |
| 6 | 388.4 ± 5.40c | 0.825 ± 0.013c | 21.32 ± 0.49c | 38.06 ± 1.37a | 428.7 ± 16.89a |
Values are means (± SE) of 3 replicate pots. Significant differences (indicated by different lowercase letters) within a column are based on a one-way analysis of variance with least significant difference (LSD) (p < 0.05)
Total nitrogen content in P. davidiana seedlings
The total nitrogen content was lower in the roots of P. davidiana seedlings treated with carboxymethyl chitosan than in the control roots (Table 4). Specifically, the total nitrogen content in the P. davidiana seedling roots decreased with increasing carboxymethyl chitosan concentrations up to 2 g/L, but increased when the carboxymethyl chitosan concentration was greater than 2 g/L. The 1, 2, and 4 g/L carboxymethyl chitosan treatments decreased the total nitrogen content in the stems and shoots of P. davidiana seedlings relative to the control levels, whereas the 6 g/L carboxymethyl chitosan treatment had no significant (p > 0.05) effect. Moreover, relative to the control level, carboxymethyl chitosan concentrations of 2 and 4 g/L decreased the total nitrogen content in leaves, whereas the 1 and 6 g/L carboxymethyl chitosan concentrations had no significant (p > 0.05) effect.
Table 4.
Total nitrogen content in P. davidiana seedlings
| Treatments (g/L) | Roots (mg/g) | Stems (mg/g) | Leaves (mg/g) | Shoots (mg/g) |
|---|---|---|---|---|
| 0 | 4.621 ± 0.044a | 4.614 ± 0.118a | 5.576 ± 0.108a | 5.163 ± 0.086a |
| 1 | 4.405 ± 0.097b | 3.971 ± 0.087b | 5.316 ± 0.199ab | 4.733 ± 0.095b |
| 2 | 2.489 ± 0.084d | 3.970 ± 0.075b | 4.884 ± 0.174c | 4.494 ± 0.143c |
| 4 | 3.493 ± 0.118c | 3.838 ± 0.120b | 5.101 ± 0.049bc | 4.554 ± 0.080bc |
| 6 | 4.416 ± 0.101b | 4.559 ± 0.094a | 5.391 ± 0.177a | 5.033 ± 0.120a |
Values are means (± SE) of 3 replicate pots. Significant differences (indicated by different lowercase letters) within a column are based on a one-way analysis of variance with least significant difference (LSD) (p < 0.05)
Total phosphorus content in P. davidiana seedlings
Relative to the control levels, the 2 g/L carboxymethyl chitosan treatment significantly increased (p < 0.05) the total phosphorus content in the P. davidiana seedling roots, stems, leaves, and shoots by 10.90%, 14.04%, 16.43%, and 15.45%, respectively (Table 5). The 1, 4, and 6 g/L carboxymethyl chitosan concentrations had no significant (p > 0.05) effect on the total phosphorus content in the roots and stems. Regarding the leaves and shoots, the 1 g/L carboxymethyl chitosan treatment decreased the phosphorus content relative to the control levels, whereas the 4 g/L carboxymethyl chitosan treatment had the opposite effect and the 6 g/L carboxymethyl chitosan treatment had no significant (p > 0.05) effect.
Table 5.
Total phosphorus content in P. davidiana seedlings
| Treatments (g/L) | Roots (mg/g) | Stems (mg/g) | Leaves (mg/g) | Shoots (mg/g) |
|---|---|---|---|---|
| 0 | 4.576 ± 0.132b | 4.104 ± 0.169b | 4.375 ± 0.121d | 4.259 ± 0.057d |
| 1 | 4.656 ± 0.101b | 4.267 ± 0.104b | 4.580 ± 0.071bc | 4.444 ± 0.007c |
| 2 | 5.075 ± 0.159a | 4.680 ± 0.110a | 5.094 ± 0.133a | 4.917 ± 0.046a |
| 4 | 4.712 ± 0.138b | 4.367 ± 0.161b | 4.738 ± 0.108b | 4.577 ± 0.085b |
| 6 | 4.607 ± 0.107b | 4.108 ± 0.131b | 4.525 ± 0.089cd | 4.346 ± 0.049cd |
Values are means (± SE) of 3 replicate pots. Significant differences (indicated by different lowercase letters) within a column are based on a one-way analysis of variance with least significant difference (LSD) (p < 0.05)
Total potassium content in P. davidiana seedlings
The 1, 2, 4, and 6 g/L carboxymethyl chitosan treatments significantly increased (p < 0.05) the total potassium content in the roots of P. davidiana seedlings by 5.33%, 13.72%, 12.27%, and 5.23%, respectively, relative to the control level (Table 6). The 1, 2, and 4 g/L carboxymethyl chitosan concentrations also increased the total potassium content in the stems and shoots of P. davidiana seedlings, but the exposure to 6 g/L carboxymethyl chitosan had no significant (p > 0.05) effect. The 2 and 4 g/L carboxymethyl chitosan concentrations increased the total potassium content in the leaves of P. davidiana seedlings, whereas the 1 and 6 g/L carboxymethyl chitosan concentrations had no significant (p > 0.05) effect.
Table 6.
Total potassium content in P. davidiana seedlings
| Treatments (g/L) | Roots (mg/g) | Stems (mg/g) | Leaves (mg/g) | Shoots (mg/g) |
|---|---|---|---|---|
| 0 | 39.21 ± 0.94c | 33.79 ± 0.70c | 44.66 ± 0.90c | 39.99 ± 0.172d |
| 1 | 41.30 ± 1.09b | 37.06 ± 1.32b | 45.96 ± 1.16c | 42.11 ± 0.787c |
| 2 | 44.59 ± 1.25a | 41.36 ± 1.57a | 54.69 ± 1.21a | 49.00 ± 1.321a |
| 4 | 44.02 ± 1.10a | 39.34 ± 0.52a | 49.95 ± 1.81b | 45.36 ± 1.071b |
| 6 | 41.26 ± 0.97b | 35.21 ± 1.09bc | 45.07 ± 0.51c | 40.84 ± 0.748cd |
Values are means (± SE) of 3 replicate pots. Significant differences (indicated by different lowercase letters) within a column are based on a one-way analysis of variance with least significant difference (LSD) (p < 0.05)
Soil pH and available nutrients
The soil pH decreased in response to the treatment of P. davidiana seedlings with carboxymethyl chitosan, with the lowest pH resulting from the 2 g/L carboxymethyl chitosan treatment (Table 7). Relative to the control level, the 1, 2, and 4 g/L carboxymethyl chitosan treatments decreased the soil alkaline nitrogen concentration, especially at 2 g/L carboxymethyl chitosan, whereas the 6 g/L carboxymethyl chitosan treatment had no significant (p > 0.05) effect (Table 7). The application of carboxymethyl chitosan increased the available phosphorus and available potassium concentrations of the soil, with peak concentrations at 2 g/L carboxymethyl chitosan.
Table 7.
Soil pH and nutrient availability
| Treatments (g/L) | pH value | Alkaline nitrogen (mg/kg) | Available phosphorus (mg/kg) | Available potassium (mg/kg) |
|---|---|---|---|---|
| 0 | 7.82 ± 0.04a | 51.41 ± 0.66a | 11.56 ± 0.23e | 10.78 ± 0.30d |
| 1 | 7.67 ± 0.01c | 47.98 ± 0.92b | 16.78 ± 0.36c | 14.01 ± 0.41c |
| 2 | 7.58 ± 0.03d | 44.28 ± 1.04c | 19.55 ± 0.56a | 22.34 ± 0.87a |
| 4 | 7.64 ± 0.02c | 48.06 ± 1.89b | 18.07 ± 0.35b | 15.00 ± 0.52b |
| 6 | 7.71 ± 0.01b | 50.96 ± 1.22a | 13.97 ± 0.46d | 13.93 ± 0.44c |
Values are means (± SE) of 3 replicate pots. Significant differences (indicated by different lowercase letters) within a column are based on a one-way analysis of variance with least significant difference (LSD) (p < 0.05)
Discussion
Plant hormones can regulate physiological and biochemical processes. Additionally, they can enhance plant stress resistance to some extent to ensure strong seedling growth and development, even under adverse environmental conditions (Mo and Gan 2017; Zhou et al. 2018). A previous study revealed that chitosan is a biostimulant that functions similarly to plant hormones to promote growth and increase the root and shoot biomasses of strawberry (Rahman et al. 2018). In the current study, the application of 1, 2, and 4 g/L carboxymethyl chitosan increased the P. davidiana seedling root, stem, leaf, and shoot biomasses, with the highest increases resulting from the 2 g/L carboxymethyl chitosan treatment. In contrast, the 6 g/L carboxymethyl chitosan treatment had no significant effect on P. davidiana seedling biomass. These results were consistent with those of a previous study (Hao et al. 2014). Thus, the application of relatively low carboxymethyl chitosan concentrations (1–4 g/L) can promote P. davidiana seedling growth, whereas higher carboxymethyl chitosan concentrations (> 6 g/L) may have the opposite effect.
Chlorophylls and carotenoids are important factors affecting the photosynthetic rate of plant leaves. The photosynthetic pigment content is an important indicator of changes to the photosynthetic capacity and physiological activity of plants (Wang 2000). An earlier investigation confirmed that a deacetylation chitosan treatment substantially increases the chlorophyll content in Ziziphus acidojuba seedlings, thereby enhancing photosynthetic activities (Zhang et al. 2010). Under drought conditions, the application of oligo-chitosan significantly increases the chlorophyll and carotenoid contents in potato plants (Muley et al. 2019). In the current study, carboxymethyl chitosan treatments increased the chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents in P. davidiana seedlings, particularly at 2 g/L carboxymethyl chitosan, indicating that carboxymethyl chitosan might promote the synthesis of photosynthetic pigments and enhance the photosynthetic capacity of P. davidiana seedlings. These results are consistent with the findings of earlier studies (Zhang et al. 2010; Muley et al. 2019).
Under normal conditions, plants rely on an endogenous free-radical scavenging system to maintain the production and elimination of reactive oxygen species in the cell, with SOD, POD, and CAT representing important components of this system (Huang et al. 2018). In the current study, carboxymethyl chitosan enhanced the SOD and CAT activities of P. davidiana seedlings, with peak activities induced by 2 g/L carboxymethyl chitosan. Therefore, carboxymethyl chitosan might enhance the stress resistance of P. davidiana seedlings. In plants, free proline and soluble protein are important osmotic adjusters that can increase the number of functional proteins in plant cells at high temperatures and under alkaline-saline conditions, maintain the osmotic balance between cell protoplasts and the environment, and stabilize the membrane system, all of which enhance the stress resistance of plants (Gao et al. 2018). Additionally, MDA is a membrane lipid peroxidation product that can reflect the degree of damage to cell membranes (Cheng et al. 2015). The application of chitosan decreases the MDA content in potato seedlings under drought conditions (Jiao et al. 2012). Low chitosan concentrations decrease the MDA content in safflower and sunflower seedlings, indicating that chitosan can inhibit lipid peroxidation (Jabeen and Ahmad 2013). In the current study, carboxymethyl chitosan increased the soluble protein content in P. davidiana seedlings. However, carboxymethyl chitosan decreased the MDA and proline contents when applied at low concentrations (1–4 g/L), but had no significant effect when applied at a higher concentration (6 g/L). These results were the same as those of previous studies (Jiao et al. 2012; Jabeen and Ahmad 2013), further indicating that suitable carboxymethyl chitosan treatments can enhance the stress resistance of P. davidiana seedlings.
Plant hormones can regulate growth and development by influencing the absorption of nutrients (Jiang et al. 2018). Spraying water spinach with growth regulators (e.g., IAA, 6-BA, and GA3) can promote the absorption and use of nitrogen and phosphorus (Yuan et al. 2012). Other studies confirmed that 1 µM IAA can increase the sulfur and calcium contents in alfalfa roots, stems, and leaves (López et al. 2007), whereas 10 µM salicylic acid can increase the calcium and phosphorus content in Vallisneria natans (Lour.) Hara leaves (Wang et al. 2011). The data presented herein revealed that the application of carboxymethyl chitosan on P. davidiana seedlings decreased the soil pH and also decreased the soil alkaline nitrogen concentration to some extent, with 2 g/L carboxymethyl chitosan having the strongest effect. In contrast, carboxymethyl chitosan treatments of P. davidiana seedlings increased the soil available phosphorus and potassium concentrations, especially at 2 g/L carboxymethyl chitosan. These results imply that carboxymethyl chitosan can alter the root exudates by modifying plant physiological processes and indirectly affect the soil pH and nutrient availability. In this study, we observed that carboxymethyl chitosan decreased the total nitrogen content and increased the total phosphorus and potassium contents in P. davidiana seedlings to some extent, especially in response to the 2 g/L carboxymethyl chitosan treatment. These observations are consistent with the reported effects of plant hormones (Yuan et al. 2012; López et al. 2007; Wang et al. 2011). Consequently, like plant hormones, carboxymethyl chitosan can alter the absorption of nutrients by plants via physiological changes.
Conclusions
The application of carboxymethyl chitosan promotes P. davidiana seedling growth by increasing the biomass and photosynthetic capacity and enhancing stress resistance, with the optimal effects induced by 2 g/L carboxymethyl chitosan. Moreover, carboxymethyl chitosan treatments can also promote the absorption of phosphorus and potassium by P. davidiana seedlings, while decreasing the nitrogen uptake to some extent. Future studies should focus on the mechanisms underlying the effects of carboxymethyl chitosan on the nutrient uptake by P. davidiana seedlings.
Acknowledgements
We thank Liwen Bianji, Edanz Editing China (www.liwenbianji.cn/ac) for editing the English text of a draft of this manuscript. This work was financially supported by the National Key Research and Development Plan of China (2018YFD0201400).
Author contributions
DDX and HYL performed the experiments, analysed the data, and drafted the manuscript. LJL planted and managed the materials in the field. MAL, QXD and JW inoculated the seedlings and helped with sampling. XLL, HHD, DL and HX conceived the study, participated in its design and coordination, and helped draft the manuscript. All authors read and approved the final manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare no competing interests, including financial and non-financial interests.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- Bao SD. Soil agrochemical analysis. Beijing: China Agriculture Press; 2000. [Google Scholar]
- Cheng XD, Sui YH, Zhang J. Effects of salicylic acid on activities of antioxidant enzyme and osmolytes of pepper seedlings under nitrate stress. J Anhui Sci Technol Univ. 2015;29(6):56–60. [Google Scholar]
- Feng QX, Zhao XW, Chen ZZ, Wang MZ, Liu LX (2018) Research progress of chitosan and its application. Sci Technol Food Ind 39(21):333–336, 341
- Gao F, Xie Y, Shen YQ, Lei Z, Wang X, Xia H, Liang D. Exogenous melatonin for NaCl stress with antioxidant enzymes and osmotic substances of Aclinidia deliciosa seedlings. J Zhejiang A F Univ. 2018;35(2):291–297. [Google Scholar]
- Guan YJ, Hu J, Wang XJ, Shao CX. Seed priming with chitosan improves maize germination and seedling growth in relation to physiological changes under low temperature stress. J Zhejiang Univ-Sc B. 2009;10(6):427–433. doi: 10.1631/jzus.B0820373. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hao ZB, Cang J, Xu Z. Plant physiology experiment. Haibin: Harbin Institute of Technology Press; 2004. [Google Scholar]
- Hao LL, Wang XQ, Zhang XR, Zhu QZ (2014) Effect of chitosan on growth and drought resistance of wheat seedlings under drought stress. Resour Dev Mark 30(8):908–909, 1005
- Hu JW, Liu H, Ma XM, Song T. Antibacterial, inducing and promoting effects of chitosan and its application in agriculture. Jiangsu Agric Sci. 2018;46(15):1–5. [Google Scholar]
- Huang WC, Fan YB, Wang YC. Low Temperature stress and maize seedlings: effect on antioxidant enzyme system and osmotic regulation. Chin Agric Sci Bull. 2018;34(24):6–12. [Google Scholar]
- Jabeen N, Ahmad R. The activity of antioxidant enzymes in response to salt stress in safflower (Carthamus tinctorius L.) and sunflower (Helianthus annuus L.) seedlings raised from seed treated with chitosan. J Sci Food Agric. 2013;93:1699–1705. doi: 10.1002/jsfa.5953. [DOI] [PubMed] [Google Scholar]
- Jiang Y, Zhao Y, Sun QJ, Li ZW (2018) Application of plant growth regulators on plant growth and development. Heilongjiang Sci 9(24):4–7, 11
- Jiao ZL, Li Y, Li JJ, Xu XY, Li H, Lu DQ, Wang JY. Effects of exogenous chitosan on physiological characteristics of potato seedlings under drought stress and rehydration. Potato Res. 2012;55:293–301. [Google Scholar]
- Liu J, Liu YQ, Li J, Sun SX, Wang YQ. Effects of alkali stress on Prunus davidiana (Carr.) leaf morphological structure and photosynthetic characteristics. Southwest China J Agric Sci. 2017;30(2):327–332. [Google Scholar]
- López ML, Peralta-Videa JR, Benitez T, Duarte-Gardea M, Gardea-Torresdey JL. Effects of lead, EDTA, and IAA on nutrient uptake by Alfalfa plants. J Plant Nutr. 2007;30(8):1247–1261. [Google Scholar]
- Lu JN. Research advance on the applications of chitosan in agricultural production. China Plant Prot. 2008;28(2):16–18. [Google Scholar]
- Ma ZX, Garrido-Maestu A, Jeong KC. Application, mode of action, and in vivo activity of chitosan and its micro- and nanoparticles as antimicrobial agents: a review. Carbohydr Polym. 2017;176:257–265. doi: 10.1016/j.carbpol.2017.08.082. [DOI] [PubMed] [Google Scholar]
- Mo KM, Gan Y. Effects of different concentrations of plant growth regulators on physiological indices of Cunninghamia lanceolata seedlings. J Green Sci Technol. 2017;9:89–91. [Google Scholar]
- Muley AB, Shingote PR, Patil AP, Dalvi SG, Suprasanna P. Gamma radiation degradation of chitosan for application in growth promotion and induction of stress tolerance in potato (Solanum tuberosum L.) Carbohydr Polym. 2019;210:289–301. doi: 10.1016/j.carbpol.2019.01.056. [DOI] [PubMed] [Google Scholar]
- Park BK, Kim MM. Applications of chitin and its derivatives in biological medicine. Int J Mol Sci. 2010;11(12):5152–5164. doi: 10.3390/ijms11125152. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Rabêlo VM, Magalhães PC, Bressanin LA, Carvalho DT, dos Santos MH, Santos PRD, de Souza TC. The foliar application of a mixture of semisynthetic chitosan derivatives induces tolerance to water deficit in maize, improving the antioxidant system and increasing photosynthesis and grain yield. Sci Rep. 2019;9(1):8164. doi: 10.1038/s41598-019-44649-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Rahman M, Mukta JA, Sabir AA, Gupta DR, Mohi-Ud-Din M, Hasanuzzaman M, Miah MG, Rahman M, Islam MT. Chitosan biopolymer promotes yield and stimulates accumulation of antioxidants in strawberry fruit. PLoS ONE. 2018;13(9):e0203769. doi: 10.1371/journal.pone.0203769. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Van SN, Minh HD, Anh DN. Study on chitosan nanoparticles on biophysical characteristics and growth of Robusta coffee in green house. Biocatal Agric Biotechnol. 2013;2(4):289–294. [Google Scholar]
- Wang Z. Plant physiology. Beijing: China Agriculture Press; 2000. [Google Scholar]
- Wang C, Zhang SH, Wang PF, Hou J, Qian J, Ao YH, Lu J, Li L. Salicylic acid involved in the regulation of nutrient elements uptake and oxidative stress in Vallisneria natans (Lour.) Hara under Pb stress. Chemosphere. 2011;84:136–142. doi: 10.1016/j.chemosphere.2011.02.026. [DOI] [PubMed] [Google Scholar]
- Yang F, Hu JJ, Wu HJ, Qian YR. Chitosan enhances leaf membrane stability and antioxidant enzyme activities in apple seedlings under drought stress. Plant Growth Regul. 2009;58:131–136. [Google Scholar]
- Yu RZ, Yu XC, Wang GH. Effect of chitin on the growth and physiological characteristics of cucumber seedling. Acta Agric Boreali-occident Sin. 2003;12(4):102–104. [Google Scholar]
- Yuan JR, Li BZ, Wu JS, Li X, Xiao HA. Effects of plant growth regulators on yield, quality and nutrients absorption efficiency in water spinach. Chin Agric Sci Bull. 2012;28(22):282–286. [Google Scholar]
- Zhang JF, Li QM, Duan XF, Liu GQ, Peng ZD. Effects of chitosan on seed germination and seedling growth of Zizphus acidojuba. J Beijing For Univ. 2010;32(6):146–150. [Google Scholar]
- Zhang CL, Liu FX, Wang ZX, Liu ZZ, Jiang L. Study on ‘Xiacui’ grafting on different seedling peach rootstocks. Northern Fruits. 2019;4:9–12. [Google Scholar]
- Zhou YZ, Zhao X, Liang XH, Zheng DH, Cao TH (2018) Effects of plant growth regulators on photosynthesis and major physiological properties of maize seedlings under cold stress. Agric Sci J Yanbian Univ 40(1):1–7, 13