Inhibition of Peanut (Arachis hypogaea L.) Growth, Development, and Promotion of Root Nodulation Including Plant Nitrogen Uptake Triggered by Polyvinyl Chloride Microplastics

Abstract

Agroecosystem sustainability and global food security may be threatened by the widespread presence and distribution of microplastics (MPs). This study investigates the impact of polyvinyl chloride (PVC) microplastics with four different dosages (0.5, 1.5, 2.5, and 3.5%) on the growth, development, and nitrogen uptake of peanut (Arachis hypogaea L.), a legume that forms symbiotic relationships with nitrogen-fixing root nodules. Oxidative stress was indicated by increases in the activity of hydrogen peroxide, proline, superoxide dismutase, peroxidase, and ascorbate peroxidase of 54.3, 72.93, 135.74, 41.59, and 44.59%, respectively, for the 3.5% dose (T4) and malondialdehyde and catalase of 23.7 and 17.52%, respectively, for the 2.5% dose (T3) over the control. Peanut seedlings' growth and development were inhibited through the suppression of chlorophyll a (30.92%), chlorophyll b (36.36%), and carotenoid (25.65%) for treatment 2 (T2) and plant height (19.52% for T4), plant dry weight (46.09%), leaf number (18.86%), and branch length (59.37%) for T4. However, root nodule number, weight, and plant N content promoted 30.19-72.32, 55.88-141.16, and 1.46-7.01%, respectively, from control to T4, which may be an adaptive mechanism for legumes to overcome N deficiency through the morphological and physiological adjustments in the stressed conditions. The study outcomes may provide worthy implications for correctly managing peanut crops in PVC MP-contaminated soil, which will ensure food security and ecosystem sustainability.

Figure 1

Effects of PVC MPs on the photosynthetic pigments. (a) Chlorophyll a, (b) chlorophyll b, (c) total chlorophyll, and (d) carotenoid. Each value is expressed as mean ± standard deviation. The letters a and b show a significant (P < 0.05) difference between treatments and the control. Ct—control, T1—treatment 1 (0.5%), T2—treatment 2 (1.5%), T3—treatment 3 (2.5%), and T4—treatment 4 (3.5%).

Figure 2

Effects of PVC MPs on nodulation. (a) Number of nodules/plant. (b) Weight of nodules/plant. (c) Lb. Each value is expressed as mean ± standard deviation. The letters a–e show a significant (P < 0.05) difference between treatments and the control. Ct—control, T1—treatment 1 (0.5%), T2—treatment 2 (1.5%), T3—treatment 3 (2.5%), and T4—treatment 4 (3.5%).

Figure 3

Effects of PVC MPs on nonenzymatic and enzymatic activities. (a) Proline, (b) MDA, (c) H₂O₂, (d) POX, (e) APX, (f) CAT, and (g) SOD. Each value is expressed as mean ± standard deviation. The letters a–g show a significant (P < 0.05) difference between treatments and the control. Ct—control, T1—treatment 1 (0.5%), T2—treatment 2 (1.5%), T3—treatment 3 (2.5%), and T4—treatment 4 (3.5%).

Figure 4

FTIR spectra of (a) virgin and (b) extracted PVC MPs. SEM images of (c) virgin and (d) extracted PVC MPs.

Figure 5

Relationship between variables and different doses (Ct—control, T1—treatment 1 (0.5%), T2—treatment 2 (1.5%), T3—treatment 3 (2.5%), T4—treatment 4 (3.5%)) of PVC MPs. (a) PCA, (b) CM or correlogram, and (c) heatmap of the relative abundance of the measured variables.