Microplastics are persistent and complex contaminants and have been recognized as a global concern. Recently, increasing efforts have been devoted to studying the influence of microplastics on soils. However, the complexity of microplastics and the diversity of extraction methods result in a lack of systematic analysis and comprehensive review in this field. In this paper, we used CiteSpace software to summarize the development of this field. Then, we visualized and analyzed the knowledge structure, research hotspots, and trend directions of this field. We found that the number of publications escalated dramatically, and 281 institutions in 69 countries have published articles in this field. Among them, China was the most productive contributor. However, according to the scientific collaboration analysis, we found that more than 90% of the authors who contributed to the field had no close connection. In co-occurrence analysis for subject categories, we found that the research in this field covered environmental science, engineering, ecology, and agriculture. Additionally, the effect of soil microplastics on agriculture was the most important problem in scientific research. The keyword co-occurrence cluster analysis revealed a total of 6 clusters, including “Identification” (#0), “Microbial community” (#1), “Oxidative stress” (#2), “Adsorption” (#3), “Porous media” (#4), and “Abundance” (#5). We discussed several aspects in detail, including detection methods, characteristics, environmental effects, adsorption capacity, removal and degradation, and toxicity. According to these results, we summarized the current research hotspots and evaluated future research trends in soil microplastics. This study is the first to specifically visualize the research field, and these results provide a reference for future research in the field of soil microplastics.

Dune-interdune is the main landscape pattern of desert areas, such as the Horqin sandy land of Northeastern China. Exploring the temporal and spatial variation of the water balance is crucial for efficient vegetation restoration at the micro-landform scale. The SWMS-2D model was used to estimate the seasonal variations of the water balance including evapotranspiration, soil water storage changes, lateral flow and drainage, and to examine the effects of micro-landforms (i.e., the top, upper, down, and bottom positions of the dune slope, and the interdune lowland area) on these components from May to October 2013 and 2015. Results showed that the soil water content was sensitive to rainfall pulses, particularly large precipitation events. Over 70% of the total evapotranspiration occurred from June to August, with a maximum daily value of 6.56 mm. At a monthly scale, evapotranspiration was not synchronous with precipitation. The ratio of evapotranspiration to precipitation was 1.84, 0.39, 2.49, 0.93, 2.26, and 1.14 in May, June, July, August, September, and October 2013 (a wet year), respectively; and 2.40, 1.11, 0.69, 2.14, 1.07, and 1.11 in 2015 (a dry year), respectively. The components of the water balance were significantly different among different micro-landforms. Evapotranspiration of a lowland area was greater than that in other micro-landforms, and the value in the wet year (2013) was significantly greater than that in the dry year (2015). However, water consumption in the lowland area was similar in both years. At the top, upper, down, and bottom positions of the dune slope, the ratio of evapotranspiration to precipitation in the wet year (2013) was 96%, 97%, 86%, and 96%, respectively; while in the dry year (2015), the ratio was 103%, 103%, 88%, and 104%. Therefore, in the dry year, evapotranspiration was generally larger than precipitation, indicating that almost all water from precipitation was evaporated. The lateral flow of the root zone from top to bottom accounted for only a small portion of water budget at the growing season scale. The results could be generalized to other similar region with corresponding model calibration, and would help to reveal seasonal variations of water balance components under the local topography, climate, soil, and vegetation conditions.

Background: The Horqin Sandy Land represents a fragile semi-arid ecosystem where sand-fixing trees play a crucial role in combating desertification. However, the assembly mechanisms and interactions of microbiota in sand-fixing plants along the soil–plant continuum remain unknown.,Methods: This study used high-throughput sequencing to analyze the diversity, composition, assembly processes, network structure and source-sink interactions of bacterial and fungal communities in the leaf endosphere, phyllosphere, rhizosphere,soil and bulk soil of the three sand-fixing trees: Pinus sylvestris var. mongolica (PSM), Populus simonii (PS), and Xanthoceras sorbifolium (XS).,Results: We found that bacterial and fungal community richness and diversity in rhizosphere soil and bulk soil were higher than in the leaf endosphere and phyllosphere across three sand-fixing tree species. Plant niches had more effect on shaping microbial community diversity (α and β) than host sand-fixing trees species. At the phylum level, Proteobacteria and Actinobacteria were the major bacterial phyla, while Ascomycota and Basidiomycota were the dominant fungal phyla across four plant niches of three sand-fixing tree species. The relative abundance of these major bacterial and fungal phyla differed markedly between the belowground compartments (rhizosphere soil and bulk soil) and the aboveground compartments (leaf endosphere and phyllosphere). Comparison of normalized stochasticity ratio (NST) revealed that the assembly of bacterial and fungal communities in the leaf endosphere was dominated by deterministic processes, whereas community assembly in the phyllosphere was dominated by stochastic processes. In terms of network complexity, the avgK values of bacterial and fungal networks in Populus simonii (PS) progressively decreased from bulk soil to rhizosphere soil, phyllosphere, and leaf endosphere. However, for Pinus sylvestris var. mongolica (PSM) and Xanthoceras sorbifolium (XS), the bacterial network complexity was highest in phyllosphere, the complex fungal co-occurrence networks were observed in the rhizosphere soil. Overall, the leaf endosphere exhibited low network complexity in bacterial and fungal communities. Microbial source tracking revealed source-sink relationships within aboveground (between the leaf endosphere and phyllosphere) and belowground compartments (between rhizosphere soil and bulk soil), but source contributions between them were negligible (<1%).,Conclusion: These results suggest that the sand-fixing tree species in the Horqin Sandy Land have evolved a compartmentalized survival strategy.