Fanrong Meng

Microplastic pollution in terrestrial ecosystems is a growing concern due to its potential influences on soil properties and crop growth. Little is known about the effects of microplastics on the microbiome in the rhizosphere. Here, we studied the effects of two types of microplastics (MPs), low density polyethylene (LDPE-MPs) and biodegradable microplastic (Bio-MPs) of poly-butylene-adipate-co-terephthalate (PBAT) mixed with polylactic acid (PLA), on rhizosphere bacterial communities of Phaseolus vulgaris at doses of 0.5 %, 1.0 % and 2.5 % (w/w, dry weight ratio between MPs and soil). Bio-MPs and LDPE-MPs showed significant higher α-diversity (Chao 1, ACE, Shannon and Simpson) than control. For each type of microplastic material, 2.5 % of LDPE-MPs and Bio-MPs showed lowest α-diversity as compared to doses of 0.5 % and 1.0 %, indicating 2.5 % dose of MPs might pose selective effect on rhizosphere bacterial communities. β-Diversity of 1.0 % and 2.5 % Bio-MPs were distinctive from the control and other treatments. Microplastics also affected the relative abundance at family level, i.e. as compared to control, Comamonadaceae was higher in all the MPs treatments, Rhizobiaceae was highest in 2.5 % LDPE-MPs and lowest in 2.5 % Bio-MPs. LefSe results showed, as compared to control, Bio-MPs induced more indictive taxa than LDPE-MPs. Our findings evidenced that LDPE-MPs and Bio-MPs exerted profound effects on rhizosphere bacterial communities, and these effects might have far-reaching effects on soil nutrient cycling and plant health in agroecosystems.

Agricultural microplastic pollution has become a growing concern. Unfortunately, the impacts of microplastics (MPs) on agricultural soil carbon and nitrogen dynamics have not been sufficiently reported. In an attempt to remedy this, we conducted a 105-day out-door mesocosm experiment in a soil-plant system using sandy soils amended with two types of MPs, low-density polyethylene (LDPE-MPs) and biodegradable (Bio-MPs), at concentrations of 0.0% (control), 0.5%, 1.0%, 1.5%, 2.0% and 2.5% (w/w, weight ratio of microplastics to air-dry soil). Soil organic matter (SOM), dissolved organic carbon (DOC), permanganate oxidizable carbon (POXC), available nitrogen (AN) of N-NH4+ and N-NO3−, and dissolved organic nitrogen (DON) were measured on day 46 (D46) and 105 (D105) of the experiment. SOM was also measured after microplastics were mixed into soils (D0). For LDPE-MPs treatments, SOM on D0, D46 and D105 showed no significant differences, while for Bio-MPs treatments, SOM significantly (p < 0.05) decreased from D0 to D46. Compared to the control, soil POXC was significantly (p = 0.001) lowered by 0.5%, 1.0% and 2.5% LDPE-MPs and ≥ 1.0% Bio-MPs on D105. LDPE-MPs showed no significant effects on soil DOC and nitrogen cycling. 2.0% and 2.5% Bio-MPs showed significantly higher (p < 0.001) DOC and DON (on D46 and D105) and ≥1.5% Bio-MPs showed significantly lower (p = 0.02) AN (on D46). Overall, Bio-MPs exerted stronger effects on the dynamics of soil carbon and nitrogen cycling. In conclusion, microplastics might pose serious threats to agroecosystems and further research is needed.

Although concerns surrounding microplastics (MPs) in terrestrial ecosystems have been growing in recent years, little is known about the responses of plant growth to MPs pollution. Here, we conducted a pot experiment in a net house under natural condition by adding two types of MPs, low-density polyethylene (LDPE-MPs) and polylactic acid (PLA) mixed with poly-butylene-adipate-co-terephthalate (PBAT, Bio-MPs), to sandy soil at 5 doses (0.5%, 1.0%, 1.5%, 2.0%, 2.5% ω/ω dry soil weight). The effects of LDPE-MPs and Bio-MPs on common bean (Phaseolus vulgaris L) were tested. Compared to control (no MPs addition), LDPE-MPs showed no significant effects on shoot, root and fruit biomass while ≥1.0% LDPE-MPs showed significant higher specific root nodules (n·g−1 dry root biomass) and only 2.5% LDPE-MPs showed significant higher specific root length (cm·g−1 dry root biomass). 1.0% LDPE-MPs caused significant higher leaf area and 0.5% LDPE-MPs caused significant lower leaf relative chlorophyll content. For Bio-MPs treatment, compared to control, ≥1.5% Bio-MPs showed significant lower shoot and root biomass. ≥2.0% Bio-MPs showed significant lower leaf area and fruit biomass. All Bio-MPs treatments showed significant higher specific root length and specific root nodules as compared to control. The results of the current research show that both MPs induced the responses of common bean growth, and ≥1.5% Bio-MPs exerted stronger effects. Further studies of their ecological impacts on soil-plant systems are urgently needed.

Background Inappropriate disposal of the plastic mulching debris could create macroplastics (MaPs) and microplastics (MiPs) pollution in agricultural soil. Methods To study the effects of farming systems on accumulation and distribution of agricultural plastic debris, research was carried out on two farming systems in Northwest China. Farming in Wutong Village (S1) is characterized by small plots and low-intensity machine tillage while farming in Shihezi (S2) is characterized by large plots and high-intensity machine tillage. In September 2017, we selected six fields in S1, three fields with 6–8 years of continuous plastic mulching (CM) as well as three fields with over 30 years of intermittent mulching (IM). In S2, we selected five cotton fields with 6, 7, 8, 15 and 18 years of continuous mulching. In both regions, MaPs and MiPs from soil surface to 30 cm depth (0–30 cm) were sampled. Results The results showed that in S1, MaPs mass in fields with 6–8 years CM (i.e., 97.4kg·ha⁻¹) were significantly higher than in fields with 30 years IM (i.e., 53.7 kg·ha⁻¹). MaPs in size category of 10–50 cm² accounted for 46.9% in fields of CM and 44.5% in fields of IM of total collected MaPs number. In S2, MaPs mass ranged from 43.5 kg·ha⁻¹ to 148 kg·ha⁻¹. MaPs in size category of 2–10 cm² account for 41.1% of total collected MaPs number while 0.25–2 cm² accounted for 40.6%. MiPs in S1 were mainly detected in fields with over 30 years of intermittent mulching (up to 2,200 particles·kg⁻¹ soil), whereas in S2 were detected in all fields (up to 900 particles·kg⁻¹ soil). The results indicated farming systems could substantially affect the accumulation and distribution of agricultural plastic debris. Continuous plastic mulching could accumulate higher amount of MaPs than intermittent plastic mulching. High-intensity machine tillage could lead to higher fragmentation of MaPs and more severe MiPs pollution. These results suggest that agricultural plastic regulations are needed.