Combined Effect of Microplastics and Cd Alters the Enzymatic Activity of Soil and the Productivity of Strawberry Plants

Abstract

The synergistic effect between heavy metals and microplastics can affect soil properties as well as plant performance and yield. The objective of this study was to evaluate the combined effect of microplastics and cadmium on a soil-plant system. Specifically, we proposed to explore changes in soil microbiological activity, the growth and yield parameters of strawberry plants, and to evaluate the accumulation of these pollutants in the soil and root system. Plants were planted in clay pots under greenhouse conditions. The experiment was set up as a completely randomized design, with four treatments (Control; MPs; Cd; and Cd + MPs) and five replicates. The results showed that MPs and/or Cd affected plant growth, plant biomass, the number of fruits, root characteristics, dehydrogenase activity, acid phosphatase, and microbial biomass, and increased the accumulation of Cd in the roots and soil. The increased bioavailability of Cd, due to the presence of microplastics, could explain the observed negative effects on soil properties and the performance of strawberry plants.

Keywords: Andisol; Fragaria × ananassa; chlorophyll fluorescence; contaminated soils; enzyme activity; polyethylene; root characteristics.

Figure 1

The effect of microplastics and/or cadmium on strawberries during plant growth for: (a) plant height (cm), (b) stem diameter (cm). Different lowercase letters indicate significant differences according to the LSD Fisher test (p < 0.05). Control: no contaminants added; MPs: microplastics added; Cd: cadmium added; Cd + MPs: cadmium and microplastics added.

Figure 2

The maximum quantum yield of PSII II (Fv/Fm) measured in strawberry plants exposed to single and combined pollutants (a) during the entire experimental period, and (b) on an average day. Treatments correspond to: control (blue): no contaminants added; MPs (green): microplastics added; Cd (orange): cadmium added; and Cd + MPs (grey): cadmium and microplastics added.

Figure 3

The root characteristics of strawberry plants in response to soil contamination with MPs and Cd. (a) Root length; (b) root surface area; (c) root volume; (d) root biomass. Control: no contaminants added; MPs: microplastics added; Cd: cadmium added; and Cd + MPs: a combined application of cadmium and microplastics. Different lowercase letters indicate significant differences according to the LSD Fisher test (p < 0.05).

Figure 4

(a) Cadmium concentration (mg kg⁻¹ dry weight) in strawberry roots for each treatment. (b) The concentration of cadmium in the soil for each treatment. Control: no contaminants added; MPs: microplastics added; Cd: cadmium added; and Cd + MPs: a combined application of cadmium and microplastics. Different lowercase letters indicate significant differences according to the LSD Fisher test (p < 0.05).

Figure 5

The correlation matrix for soil variables and plant performance parameters. SR: soil respiration; MBC: microbial biomass C; DA: dehydrogenase activity; UA: urease activity; APA: acid phosphatase activity; Cd: cadmium concentration in the soil; Inflo: the number of inflorescences; Stol: the total number of stolons; L: stolon length; F: the total number of fruit; W: fruit weight; DR biomass: dry root biomass; DS biomass: dry stem biomass; RL: root length; SRA: root surface area; RV: root volume; Fv/Fm: the maximum quantum yield of PSII II; PH: plant height; and SD: stem diameter.

Figure 6

Principal component analysis (PCA) of SR: soil respiration; MBC: microbial biomass C; DA: dehydrogenase activity; UA: urease activity; APA: acid phosphatase activity; Cd: Cd concentration in the soil; Inflo: the number of inflorescences; Stol: the total number of stolons; L: stolon length; F: the total number of fruit; W: fruit weight; DR biomass: dry root biomass; DS biomass: dry stem biomass; RL: root length; SRA: root surface area; RV: root volume; Fv/Fm: the maximum quantum yield of PSII II; PH: plant height; and SD: stem diameter. (a) PCA of variables. (b) PCA of individuals.