Winter cover crops have been shown to promote the accumulation of microbial biomass carbon and nitrogen, enhance nutrient cycling, reduce erosion, improve ecosystem stability, etc. In the black soil area of Northeast China, Triticum aestivum L., Medicago sativa L., Vicia villosa Roth., Triticum aestivum L. and Medicago sativa L. mixed planting, Triticum aestivum L. and Vicia villosa Roth. mixed planting, and winter fallow fields (CK) were selected to investigate the effects of winter cover crops on soil total carbon and nitrogen and microbial biomass carbon and nitrogen. The results showed that (1) after seasonal freeze-thaw, the rate of change in SOC (−2.49~6.50%), TN (−1.54~5.44%), and C/N (−1.18~1.16%) was less than that in SMBC (−80.91~−58.33%), SMBN (−65.03~332.22%), and SMBC/SMBN (−45.52~−90.03%); (2) winter cover crops not only alleviated the negative effects of seasonal freeze-thaw, which reduces SMBC and qMBC, but also increased SMBN and qMBN; (3) there was an extremely significant (p < 0.01) positive correlation between SOC and TN, a significant (p < 0.05) negative correlation between SMBC and SMBN, and there was no significant correlation between SOC and SMBC or between TN and SMBN; (4) alkali-hydrolysable nitrogen had the greatest impact on SOC and TN, while the soil’s saturation degree had the greatest impact on SMBC and SMBN; and (5) the Triticum aestivum L. monoculture was the most effective in conserving soil microbial carbon and nitrogen. In conclusion, winter cover crops can mitigate the reduction in soil microbial biomass carbon caused by seasonal freeze-thaw and also increase the soil microbial nitrogen content in the black soil region of Northeast China, of which Triticum aestivum L. monoculture showed the best performance.

The thinning, leaning, and hardening of arable land in the black soil region of Northeast China has brought serious challenges to the sustainable development of agriculture. It is of great significance to explore suitable conservation tillage for the conservation and sustainable utilization of black soil resources actively. The topsoil of the cropland in the northeastern part of the Songnen Plain with winter fallow (CK), planted alfalfa, and planted winter wheat was used as the research object to analyze the changes in the soil aggregate composition, nutrients, and enzyme activities before and after freeze–thaw, respectively, and to investigate the effect of winter cover crops on the improvement of the quality of the black soil cropland. Compared with the winter fallow field, (1) planting alfalfa significantly increased the mechanical stability of 1–2 mm and 0.25–1 mm particle size aggregates (about 3 times and 25 times over), and planting winter wheat increased the water stability of 0.25–1 mm particle size aggregates significantly (2.7 times over); (2) planting alfalfa and winter wheat increased the soil C/N ratio of >2 mm and 1–2 mm particle size aggregates, and the increment in the C/N ratio in >2 mm particle size aggregates remarkably increased, by 203.6% and 362.7%, respectively; (3) planting alfalfa significantly enhanced the soil invertase activity and urease activity in >2 mm and 0.25–1 mm particle size aggregates, and planting winter wheat significantly enhanced the catalase activity in 0.25–1 mm particle size aggregates. In conclusion, planting winter cover crops during the winter fallow period can maintain and promote the mechanical and water stability of medium and large (0.25–1 mm,1–2 mm) soil aggregates, increase the carbon content and C/N ratio of larger (1–2 mm, >2 mm) aggregates, and enhance the enzyme activity of small and medium (0.25–1 mm, <0.25 mm) aggregates to varying degrees. The results of the study can provide a reference for the promotion of basic research on and technology for winter cover crops in the black soil region.

Plants play a crucial role in soil fixation and enhancement of slope stability, and saline–alkaline stress is one of the main restrictions inhibiting plant growth and development. At present, there is a lack of research on the effects of saline–alkaline composite stress on the mechanical properties of the root system and the erosion resistance of the root–soil complex. In this study, three gradients of saline–alkaline composite stress treatments and a control of saline-free treatment was set up for Oenothera biennis, Perilla frutescens, Echinops sphaerocephalus, and Lychnis fulgens. The plant salt damage rate, osmotic index, antioxidant enzyme activity and plant root morphological indicators were measured. The biomechanical characteristics were determined by stretching tests, the resistance of the plant was measured by a whole-plant vertical uprooting test, and the anti-erosion capacity of the root soil composite was measured by scrubbing test. The results showed that, at 200 mM, the salt damage index and salt damage rate of the four plants, in descending order, were as follows: E. sphaerocephalus < L. fulgens < O. biennis < P. frutescens. Among them, SOD of Perilla frutescens did not play an obvious protective role, and the substantial changes in CAT and POD, as well as the content of soluble sugars, soluble proteins, and proline, showed its sensitivity to saline and alkaline stresses. Root growth was also significantly suppressed in all four plants, the 100- and 200-mM concentrations of saline solution significantly reduced the average tensile strength of O. biennis and P. frutescens, while the saline–alkali solution of 200 mM significantly reduced the elongation of E. sphaerocephalus and L. fulgens, and significantly elevated the soil detachment rate of the root–soil composite for E. sphaerocephalus. Additionally, all three concentrations of saline treatments significantly reduced the pullout resistance of all 4 plants. There was a negative power rate relationship between tensile resistance and root diameter in four plant species, while the relationship between tensile strength and root diameter showed a negative power law only for L. fulgens treated with 0–50 mM saline solution. There was no significant correlation between elongation and root diameter in the four plants. P. frutescens had the greatest tensile resistance and strength, as well as the lowest rate of elongation, while L. fulgens possessed the greatest pullout resistance, and both had comparable resistance to erosion of the root–soil complex. Therefore, compared to the other three plants, L. fulgens is more suitable for soil reinforcement applications on saline slopes.

Degradation of black soil areas is a serious threat to national food security and ecological safety; nevertheless, the current lack of information on the location, size, and condition of black soil farmland productivity is a major obstacle to the development of strategies for the sustainable utilization of black soil resources. We synthesized remote sensing data and geospatial thematic data to construct a farmland productivity assessment indicator system to assess the productivity of black soil cropland at the regional scale. Furthermore, we conducted research on the spatial differentiation patterns and a spatial autocorrelation analysis of the assessment results. We found that farmland productivity within this region exhibited a decline pattern from south to north, with superior productivity in the east as opposed to the west, and the distribution follows a “spindle-shaped” pattern. Notably, the Songnen and Sanjiang typical black soil subregions centrally hosted about 46.17% of high-quality farmland and 53.51% of medium-quality farmland, while the Mondong typical black soil subregion in the west predominantly consisted of relatively low-quality farmland productivity. Additionally, farmland productivity displayed a significant positive spatial correlation and spatial clustering, with more pronounced fluctuations in the northeast–southwest direction. The developed indicator system for farmland productivity can illustrate the spatial differentiation and thereby offer a valuable reference for the sustainable management of farmland resources.

Exposure to PM_2.5 poses severe risks to public health and sustainable development, with exposure inequalities exacerbated by variations in atmospheric activity and uneven regional development. However, the urban-rural inequalities and natural-human driving mechanisms underlying PM_2.5 exposure inequalities within urban agglomerations are poorly understood. Taking the Central Plains Urban Agglomeration (CPUA) in China as an example, this study investigated the spatio-temporal variations of PM_2.5 and considered its future trends. The Theil index was employed to quantify PM_2.5 exposure inequalities. An interpretable machine learning model (RF-SHAP) was applied to identify the raster natural and socioeconomic driving factors. We found that 99.68% of the CPUA exhibited a decreasing trend in ground-level PM_2.5. The overall Theil index decreased from 0.168 to 0.142, with a rural decline from 0.115 to 0.084, suggesting an overall reduction in air pollution inequalities, particularly in rural areas. Conversely, the urban Theil index increased from 0.096 to 0.208, highlighting an increasing inequality in urban PM_2.5 exposure. Resource-based cities, such as Changzhi, Jincheng, and Jiaozuo, exhibited the largest PM_2.5 exposure inequality. Elevation was identified as the dominant factor influencing overall and rural PM_2.5 exposure inequalities, while population density was the primary driver of urban inequalities. This study highlighted the differences in urban−rural PM_2.5 inequalities and their drivers at the city agglomeration scale. The aims were to mitigate PM_2.5 exposure inequalities through socio-environmental systems, provide evidence for the integrated management of PM_2.5 exposure inequalities in city agglomerations, and support regional sustainable development.