Reprogramming of microbial community in barley root endosphere and rhizosphere soil by polystyrene plastics with different particle sizes.

Polystyrene plastics is an emerging pollutant affecting plant performance and soil functioning. However, little information is available on the effects of microplastics and nanoplastics on plant root endophytic and rhizospheric soil microbial communities. Here, barley plants were grown in microplastics/nanoplastics -treated soil and the diversity, composition and function of bacteria and fungi in the root and rhizosphere soil were examined. At the seedling stage, greater changes of root endophytes were found compared with rhizosphere microorganisms under the plastic treatments. Nanoplastics decreased the richness and diversity of the fungal community, while microplastics increased the diversity of the root endophytic bacterial community. The network of the bacterial community under nanoplastics showed higher vulnerability while lower complexity than that under the control. However, the bacterial community under microplastics had a relatively higher resistance than the control. For the rhizosphere microbial community, no significant effect of plastics was found on the α-diversity index at the seedling stage. In addition, the nanoplastics resulted in higher sensitivity in the relative abundance and function of rhizosphere soil microbes than root endophytic microbes at the mature stage. Treatments of polystyrene plastics with different particle sizes reprogramed the rhizosphere and root endophytic microbial communities. Different effects of microplastics and nanoplastics were found on the diversity, composition, network structure and function of bacteria and fungi, which might be due to the variation in particle sizes. These results lay a foundation for learning the effects of polystyrene plastics with different particle sizes on the microorganisms in rhizosphere soil and plant roots, which may have important implications for the adaptation of plant-microbial holobiont in polystyrene plastics-polluted soils.

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This study aimed to examine the responses of persistent soil seed bank to future precipitation reduction of global climate change in the forest-steppe ecotone of Hulunbuir. Samples of soil seed bank were collected from 0-10 cm soil layer along a precipitation gradient. We examined the density, species composition, diversity of seed bank and their relationship with vegetation. Structural equation model was used to explore the direct impact of annual precipitation on soil seed bank and the indirect impact through vegetation, soil nitrogen, soil phosphorus, and soil pH. The results showed that seed bank density and species richness were negatively correlated with annual precipitation. The species diversity of soil seed banks in grasslands was higher than that in forests. The similarity between soil seed bank and vegetation was generally low. The results of structural equation model showed that the effects of annual precipitation on seed bank density and species richness were negative, with the standard path coefficients of -0.051 and -0.122, respectively. The direct effect of annual precipitation on seed bank density and species richness were positive. Precipitation had indirect and positive effect on seed bank density and species richness through soil nitrogen, a significantly indirect negative effect on seed bank species richness through soil pH and soil available phosphorus, and a significantly indirect negative effect on seed bank density through soil pH. The reduction of precipitation under furture climate change might alter the hedging strategies of plants. The persistent soil seed bank in the forest-steppeecotone had a potential buffering effect against future precipitation reduction.

Low temperature tolerance is impaired by polystyrene nanoplastics accumulated in cells of barley (Hordeum vulgare L.) plants.

With increasing plastic consumption, the large amount of polystyrene nanoplastics (PS-NPs) in agricultural soil may not only directly affect the plant growth, but also indirectly affect the abiotic stress tolerance in crops. In this study, the barley (Hordeum vulgare L.) was irrigated with 2 g L-1 PS-NPs (65.776 ± 0.528 nm) solution for 7 days, then subjected to low temperature (2 â„ƒ) for 24 h. The imaging of protoplasts indicated that polymethylmethacrylate nanoplastics could across the cell wall and accumulate in plant cells. The PS-NPs significantly decreased Rubisco activities and ATP production, hence limiting the photosynthetic carbon assimilation in barley under low temperature. The PS-NPs accumulated in cells also caused the significantly decreased activities of key enzymes involved in sucrolytic, glycolysis and starch metabolism pathways, including UDP-glucose pyrophorylase, ADP-Glucose pyrophosphorylase, phosphoglucomutase, glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, fructokinase and phosphofructokinase. In addition, under low temperature, the PS-NPs presence significantly reduced the activities of superoxide dismutase, ascorbate peroxidase and catalase in chloroplasts, and significantly reduced the activities of ascorbate peroxidase and catalase in mitochondria. Thus, it is suggested that the PS-NPs accumulated in plant cells impaired the low temperature tolerance in barley mainly by the negative effects on photosynthetic carbon assimilation, carbohydrate metabolism and ROS homeostasis in sub-cellular level.