The plastic mulch films used in agriculture are considered to be a major source of the plastic residues found in soil. Mulching with low-density polyethylene (LDPE) is widely practiced and the resulting macro- and microscopic plastic residues in agricultural soil have aroused concerns for years. Over the past decades, a variety of biodegradable (Bio) plastics have been developed in the hope of reducing plastic contamination of the terrestrial ecosystem. However, the impact of these Bio plastics in agroecosystems have not been sufficiently studied. Therefore, we investigated the impact of macro (around 5 mm) and micro (<1 mm) sized plastic debris from LDPE and one type of starch-based Bio mulch film on soil physicochemical and hydrological properties. We used environmentally relevant concentrations of plastics, ranging from 0 to 2% (w/w), identified by field studies and literature review. We studied the effects of the plastic residue on a sandy soil for one month in a laboratory experiment. The bulk density, porosity, saturated hydraulic conductivity, field capacity and soil water repellency were altered significantly in the presence of the four kinds of plastic debris, while pH, electrical conductivity and aggregate stability were not substantially affected. Overall, our research provides clear experimental evidence that microplastics affect soil properties. The type, size and content of plastic debris as well as the interactions between these three factors played complex roles in the variations of the measured soil parameters. Living in a plastic era, it is crucial to conduct further interdisciplinary studies in order to have a comprehensive understanding of plastic debris in soil and agroecosystems.
Low-density polyethylene (LDPE) is the most abundant source of microplastic pollution worldwide. A recent study found that LDPE decay was increased and the size of the plastic was decreased after passing through the gut of the earthworm Lumbricus terrestris (Oligochaeta). Here, we investigated the involvement of earthworm gut bacteria in the microplastic decay. The bacteria isolated from the earthworm's gut were Gram-positive, belonging to phylum Actinobacteria and Firmicutes. These bacteria were used in a short-term microcosm experiment performed with gamma-sterilized soil with or without LDPE microplastics (MP). We observed that the LDPE-MP particle size was significantly reduced in the presence of bacteria. In addition, the volatile profiles of the treatments were compared and clear differences were detected. Several volatile compounds such as octadecane, eicosane, docosane and tricosane were measured only in the treatments containing both bacteria and LDPE-MP, indicating that these long-chain alkanes are byproducts of bacterial LDPE-MP decay.
Inappropriate disposal of the plastic mulching debris could create macroplastics (MaPs) and microplastics (MiPs) pollution in agricultural soil.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.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.
Microplastics (MPs), as new pollutants in agroecosystems, have already attracted widespread attention from scientists. However, our understanding of MP geographic distribution and its influencing factors across spatial scales remains poor. Here, a regional-scale field investigation was conducted to assess the distribution characteristic of MPs in five major rice-growing regions of China, and we explored the roles of biological and abiotic factors, especially stoichiometry and microbial influences on MP distribution. MPs were observed in all sampling sites, averaging 6,390 ± 2,031 items⋅kg-1. Sizes less than 0.5 mm and black and transparent MPs dominated. Fiber, classified as one of the MP shapes, occurred most frequently. MP community analysis, firstly used in paddy soil, revealed more black MPs abundance in Henan (HE), more rayon, blue, and other colors MPs in Hunan (HN), more transparent MPs in Tianjing (TJ), and more PE MPs in Heilongjiang (DB). Higher MP community diversity was found in most south paddy soils of this study, due to a broader range of sources. C/N showed a positive relationship with pellet-shaped MP abundance and MPs of size between 2 and 5 mm (P < 0.05). Chao1 index of soil microbial communities was positively correlated with the MP abundance, MPs of size less than 0.5 mm, and fiber abundance. The minimum temperature was positively correlated with MP abundance (P < 0.05), implying the potential effects of the freeze-thaw process might exist. The regression analysis highlighted the important role of population quantity in determining MP abundance (R = 0.421, P = 0.02). This study confirmed the wide distribution of MPs in different soil depths of paddy lands in China and demonstrated that its distribution was influenced by population quantity and environmental variables, such as microbiology. These findings could provide a basis for the toxicological behavior of MPs and the potential risk to human health.
Abstract Aims and Objectives Quarantine during the COVID‐19 pandemic resulted in longer‐term sedentary behaviours and mental health problems. Our study aimed to evaluate the impact of the Otago exercise programme (OEP) on physical function and mental health among elderly with cognitive frailty during COVID‐19. Background Lockdowns and restrictions during the COVID‐19 pandemic result in longer‐term sedentary behaviours related disease and mental problem. Older people with cognitive frailty are more vulnerable to be influenced. Timely intervention may achieve better outcomes, OEP exercise was designed as a balance and muscle‐strengthening programme for elderly people. Design A parallel‐group, assessor‐blinded randomised controlled trial was performed according to CONSORT guidelines. Methods This study was conducted from July 2020 to October 2020 among 62 elderly people with cognitive frailty from a nursing home. Participants were randomly divided into an OEP group ( n = 31) or a control group ( n = 31). Both groups received sleep‐ and diet‐related health education. The OEP group also received a 12‐week group exercise programme. The Five Times Sit to Stand Test (FTSST), Berg Balance Scale (BBS), and Timed Up and Go Test (TUGT) were used to assess physical function. The Geriatric Depression Scale‐15 (GDS‐15) and the 12‐Item Short Form Health Survey Mental Component Summary (SF‐12 MCS) were used to assess mental health. Outcomes were measured at 6 and 12 weeks. Results Physical function and mental health were similar in the two groups at baseline. At 12 weeks, the OEP group (difference in change from baseline: FTSST, −2.78; TUGT, −3.73; BBS, 2.17; GDS‐15, −0.72; SF‐12 MCS, 2.58; all p < .001) exhibited significantly greater improvements than the control group (difference in change from baseline: FTSST, 1.55; TUGT, 1.66; BBS, −0.10; GDS‐15, 1.07; SF‐12 MCS, −5.95; all p < .001). Conclusion Our findings showed the OEP group had better physical function and mental health outcomes than the control group. OEP can be used to improve the physical and mental function among elderly people with cognitive frailty during the COVID‐19 pandemic. Relevance to clinical practice Otago exercise program intervention programmes should be implemented to improve physical function for cognitive frailty elderly to reduce the harm of longer‐term sedentary behaviours, and to ruduce depression symptom and improve mental health, particularly during COVID‐19 pandemic period.
Abstract [Background]The pqq genes which encodes phosphorus solubilizing from Bacillus mycoides Gnyt1 has been cloned and characterized. The role of this action on the function of pqq genes were detected. The phosphorus soluble pqq genes can secrete some specific organic activity acids to work but don’t destroy the living environment of plants such as soil. In contrast, this plants containing the pqq genes grew well, even better than other plants with lower phosphorus solubilization, in the phosphorus free medium even though its pqq genes activity and turned out phosphorus ring, while pqq dependent expression was induced.[Results]This reaserch that five pqq genes were cloned from Bacillus mycoides Gnyt1, phylogenetic analysis revealed that pBI- pqq A, pBI- pqq B, pBI- pqq C and pBI- pqq E similarly cluster with Phosphorus-soluble protein. Under the action of five promoters, each coding region of pqq A, pqq B, pqq C and pqq E from Bacillus mycoides Gnyt1 can directly participate in the phosphate solubilization of the strain, directly improving the phosphate solubilizing capacity of the plant, which have strong nitrogenase activity. Interestingly, changes in the phosphate solubilizing gene result in complete loss of the phosphate solubilization of the strain. However, the ability to dissolve the phosphorus ring and to dissolve the phosphorus was also exhibited in the medium having five phosphorus-dissolving genes.[Conclusions]The results indicated that the pqq genes were successfully cloned and a new specific phosphate-dissolving strain was formed. In this research, pqq genes were first cloned from Bacillus mycoides Gnyt1.
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