Effects of microplastics on physiological and biochemical characteristics of Sinorhizobium fredii and its ability to mobilize insoluble phosphorus in soil

doi:10.3969/j.issn.1004-1524.20250034

Acta Agriculturae Zhejiangensis ›› 2026, Vol. 38 ›› Issue (2): 317-326.DOI: 10.3969/j.issn.1004-1524.20250034

• Environmental Science • Previous Articles Next Articles

Effects of microplastics on physiological and biochemical characteristics of Sinorhizobium fredii and its ability to mobilize insoluble phosphorus in soil

CHENG Zhengming(), YU Sunjie, ZHANG Liang()

College of Chemical and Biological Engineering, Nanjing Normal University Taizhou College, Taizhou 225300, Jiangsu, China

Received:2025-01-10 Online:2026-02-25 Published:2026-03-24

Abstract

Abstract:

To investigate the effects of microplastics on the physiological and biochemical properties of rhizobia and their ability to activate insoluble phosphorus in soil, Sinorhizobium fredii was selected as the test strain. The impacts of monodisperse polystyrene microplastics (PS-MPs) at different concentrations on the growth, biofilm formation, antioxidant system, and phosphorus-solubilizing capacity of S. fredii were studied. The results showed that microplastics affected the growth of S. fredii. Treatments with 80-300 mg·L^-1 PS-MPs significantly (p<0.05) promoted biofilm formation. All PS-MPs treatments at 20-300 mg·L^-1 significantly increased the contents of hydrogen peroxide (H₂O₂) and soluble protein in S. fredii; however, the responses of different types of antioxidant enzymes and antioxidant substances varied, reflecting the complexity of the antioxidant defense mechanism in S. fredii. Additionally, PS-MPs treatments at 20-300 mg·L^-1 all led to a significant decrease in the content of available phosphorus in soil than that of the treatment without PS-MPs, indicating that microplastic pollution impaired the ability of S. fredii to activate insoluble phosphorus in soil. These results not only reveal the mechanism underlying the effects of microplastic pollution on the physiological and biochemical metabolism of S. fredii, but also provide a basis for in-depth understanding of the biological functions of rhizobia and optimization of soil phosphorus cycling.

Key words: microplastics, rhizobia, physiological and biochemical characteristics, phosphate-solubilizing ability

CLC Number:

S154.3
X53

CHENG Zhengming, YU Sunjie, ZHANG Liang. Effects of microplastics on physiological and biochemical characteristics of Sinorhizobium fredii and its ability to mobilize insoluble phosphorus in soil[J]. Acta Agriculturae Zhejiangensis, 2026, 38(2): 317-326.

Figures/Tables 7

Fig.1 Growth curve and biofilm formation of rhizobia under microplastics stress Partial concentrations in the top panel are selected for significant difference analysis to reveal the differences in the time when rhizobia in different concentration treatment groups enter the stationary phase. Dots marked without the same letters indicate significant difference at p<0.05. “*” in the bottom panel indicates significant (p<0.05) difference.

Table 1 Antioxidant enzyme activity and reactive oxygen content in rhizobia under microplastics stress

c_PS-MPs/ (mg·L^-1)	A_SOD/ (U·mg^-1)	A_POD/ (U·min^-1·mg^-1)	A_CAT/ (U·min^-1·mg^-1)	c_SA/ (μmol·g^-1)	c_HP/ (μmol·g^-1)
0	180.3±17.51 bc	45.66±8.56 ef	6.35±0.78 b	1.40±0.11 b	4.11±1.89 d
20	208.49±7.19 ab	97.93±16.06 c	5.40±0.27 bc	0.68±0.25 d	26.44±2.05 b
40	161.21±5.38 cd	136.88±8.73 b	3.49±0.21 c	1.06±0.15 c	31.79±2.32 a
80	143.03±19.69 d	35.31±4.03 f	6.52±1.84 b	1.52±0.10 b	30.97±1.17 a
100	192.6±17.91 b	94.38±1.27 cd	13.37±1.80 a	1.32±0.07 b	23.07±0.90 c
200	224.23±15.23 a	198.41±34.9 a	13.01±1.52 a	1.33±0.07 b	23.10±0.99 c
300	205.49±17.74 ab	67.69±3.71 de	11.31±0.89 a	1.93±0.09 a	30.77±2.03 a

Fig.2 Contents of ascorbic acid (AsA) and glutathione (GSH) in rhizobia under microplastics stress Bars marked without the same letters indicate significant differences at p<0.05. The same as below.

Table 2 Contents of penetrant substances in rhizobia under microplastic stress

c_PS-MPs/ (mg·L^-1)	c_SS/ (mg·g^-1)	c_SP/ (mg·g^-1)	c_MDA/ (μmol·g^-1)
0	135.08±5.23 b	6.80±0.39 e	4.57±0.22 bc
20	100.24±15.12 d	45.83±3.08 c	4.85±0.17 bc
40	87.02±1.79 d	39.56±4.49 c	4.19±1.00 c
80	129.78±18.48 b	18.72±5.77 d	4.60±0.75 bc
100	104.77±9.53 cd	66.23±1.35 b	4.75±0.39 bc
200	120.34±9.62 bc	72.89±4.29 b	5.54±0.20 b
300	174.07±5.34 a	86.09±6.00 a	7.54±0.55 a

Fig.3 pH value, acid phosphatase activity, and soluble phosphorus content in culture solution under microplastic stress

Fig.4 Soil available phosphorus content under microplastic stress

Fig.5 Results of correlation analysis pH, pH value in culture solution; ACP, Acid phosphatase activity in culture solution; SAP, Soil available phosphorus content; CSP, Soluble phosphorus content in culture solution. “*” indicates significant correlation at p<0.05.

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Effects of microplastics on physiological and biochemical characteristics of Sinorhizobium fredii and its ability to mobilize insoluble phosphorus in soil

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