Microplastics (MPs)-induced changes in soil nutrient cycling and microbial activity may pose a potential risk to soil ecosystem. Although some studies have explored these topics, there is still a large space for exploration and a relative lack of research on the mechanism by which soil health and its functions are affected by these changes. Thus, this study investigated the effects of polyethylene (PE) MPs with two particle sizes (13 μm and 130 μm) at five concentrations (0%, 1%, 3%, 6% and 10%, w/w) on soil biochemical properties and ecosystem function. The findings revealed that the exposure to 13 μm MPs significantly reduced soil respiration (Res) rate, β-glucosidase (Glu) and catalase (CAT) activity, which accompanied with enhanced urease activity and decreased soil pH, available phosphorus (AP), dissolved reactive phosphorus (DRP), dissolved organic carbon (DOC) and available potassium (AK) content in most cases. However, 130 μm MPs exerted negligible influence on the DOC and DRP content, Glu and CAT activity. High concentrations of 130 μm MPs significantly reduced soil pH, total dissolved nitrogen (TDN), AP and AK content, but significantly increased soil Res rate. Overall, soil ecosystem function was significantly reduced by the addition of MPs. The Res rate, soil AP and DRP content and Glu activity were the most important predictors of soil ecosystem function. We found that the risk posed by MPs to soil ecosystem function was dose-dependent and size-dependent. These findings underscore that MPs can alter soil functions related to soil nutrient cycling and provide further insights into MPs behavior in agroecosystems.

Excessive nitrogen (N) fertilization harms the diversity, structure, and function of the soil microbiome. Yet, whether such adverse effects can be repaired through reducing the subsequent N fertilization rate remains not completely clear so far. Here, using a long-term N-overfertilized wheat-maize cropping field, we assessed the effect of reducing various proportions of the subsequent N fertilization rate over six years on crop productivity, soil physicochemical and biochemical properties, and microbiome. Five treatments were employed in our field experiment: the farmers’ conventional N fertilization rate (zero reduction, as a control) and the reduction in the farmers’ N rate by 20%, 40%, 60%, and 100%. The results showed that moderate N reduction (20–40%) enhanced crop productivity and soil fertility but did not affect soil enzyme activity. Soil bacterial and fungal community diversity were insensitive to N fertilization reduction, whereas their community structures changed significantly, with more prominent alteration in the fungal community. Functional prediction indicated that average relative abundance of arbuscular mycorrhizal fungi increased with N fertilization reduction but that of ectomycorrhizal fungi decreased. Moderate N reduction (20–40%) enhanced species interactions and, thus, provided a more complex cross-kingdom microbial co-occurrence network. Both bacterial and fungal community assembly were governed by stochastic processes, and this was not altered by N fertilization reduction. Overall, the response of the soil microbiome to N fertilization reduction was greatly dependent on the reduced N proportion. The findings obtained here shed light on the importance of optimal N fertilization rate in the intensively cultivated, high-input grain production system.

The application of phosphate fertilizers significantly influences soil microbial communities and nutrient cycling. Soil enzymes, which are sensitive to nutrient levels, play a critical role in microbial metabolism. However, the impact of phosphate fertilizers on nutrient limitations within the microbial metabolism of agricultural soils remains poorly understood. In this study, soil samples were collected from a depth of 0–20 cm from a wheat crop subjected to a three-year field experiment with six different phosphorus (P) application rates. Soil β-glucosidase (BG) and leucine aminopeptidase (LAP) activities were highest under the P3 (60 kg P₂O₅ ha⁻¹) treatment over the three-year study period. The responses of soil N-acetyl-β-glucosaminidase (NAG) and alkaline phosphatase (AKP) to increasing P additions varied across different years. The EES C:N, C:P, and vector length were significantly greater than 1. Soil nutrient characteristics accounted for 70.71% of the variation in soil enzyme stoichiometry. The vector length and angle of soil enzymes explained by soil nutrient characteristics were 0.65 and 0.73, respectively. Among these factors, ROC exhibited the largest direct and total effect on the soil enzyme vector length and angle. These research findings offer valuable insights for the management of agricultural fertilizers. Consequently, it is recommended to enhance soil carbon levels to alleviate carbon limitations and improve P utilization efficiency.

Partial substitution of mineral N fertilizer with manure (organic substitution) is considered as an effective way to reduce N input in intensive agroecosystems. Here, based on a 3-year field experiment, we assessed the influence of different organic substitution ratios (15%, 30%, 45%, and 60%, composted chicken manure applied) on vegetable productivity and soil physicochemical and biochemical properties as well as microbiome (metagenomic sequencing) in an intensive greenhouse production system (cucumber-tomato rotation). Organic substitution ratio in 30% got a balance between stable vegetable productivity and maximum N reduction. However, higher substitution ratios decreased annual vegetable yield by 23.29–32.81%. Organic substitution (15–45%) improved soil fertility (12.18–19.94% increase in soil total organic carbon content) and such improvement was not obtained by higher substitution ratio. Soil mean enzyme activity was stable to organic substitution despite the activities of some selected enzymes changed (catalase, urease, sucrase, and alkaline phosphatase). Organic substitution changed the species and functional structures rather than diversity of soil microbiome, and enriched the genes related to soil denitrification (including nirK, nirS, and nosZ). Besides, the 30% of organic substitution obviously enhanced soil microbial network complexity and this enhancement was mainly associated with altered soil pH. At the level tested herein, organic substitution ratio in 30% was suitable for greenhouse vegetable production locally. Long-term influence of different organic substitution ratios on vegetable productivity and soil properties in intensive greenhouse system needs to be monitored.

The application of nitrification inhibitors (NIs) is an effective way to reduce soil nitrogen (N) losses and increase crop N uptake. Yet, the efficacy of NIs commonly varies with dosages, crop systems and soil environmental conditions. Hence, clarifying the suitable type and dosage of NIs is extremely important for structuring the best N management regime at a regional scale. Here, based on microcosm experiments, we evaluated the influence of three widely used NIs [Dicyandiamide, DCD; 3,4-Dimethylpyrazole phosphate, DMPP; 2-chloro-6-(trichloromethyl) pyridine, Nitrapyrin] on the nitrification activity of an intensively cultivated greenhouse soil. The results showed that both DCD and DMPP imposed a transient inhibition on nitrification (less than five days) regardless of the dosages applied, and, on the contrary, Nitrapyrin presented a persistent suppression, with a longer duration of the inhibition action by a higher dosage. Accordingly, the incorporation of Nitrapyrin at 2% of the applied N rate (w/w) is a recommendable dosage for local intensive greenhouse production. Further, we assessed the influence of various dosages of Nitrapyrin incorporation (0%, 0.25%, 0.5%, 2% and 5%) on the abundance and community of three groups of soil ammonia oxidizers [i.e., ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and completely ammonia-oxidizing bacteria (Comammox Nitrospira)] by qPCR and high-throughput amplicon sequencing. Nitrapyrin incorporation strongly lowered both the AOB and Comammox Nitrospira abundances and their community richness even at the lowest dosage. Nitrapyrin incorporation also significantly altered the community structure of all of the tested ammonia oxidizers, and the average relative abundance of some major community members (i.e., the Nitrososphaerales Clade Nitrososphaera, Nitrososphaerales Clade A, Nitrosospira briensis Clade, Nitrosospira multiformis Clade, Comammox Nitrospira Clade A.2 and Comammox Nitrospira Clade A-associated) obviously responded to Nitrapyrin incorporation. Overall, our findings indicated that AOB and Comammox Nitrospira were more sensitive to Nitrapyrin incorporation as compared with AOA. The results obtained here highlight the importance of optimizing the type and dosage of NIs for N fertilization management in intensive greenhouse vegetable production. Nitrapyrin incorporation inhibits soil nitrification probably by suppressing the Nitrosospira multiformis Clade in the AOB community at the level tested herein.

Discarded face masks represent an emerging plastic pollutant in terrestrial ecosystems, however, their comprehensive ecological impacts on soil processes remain poorly understood. This study systematically investigates the impacts of centimeter-sized disposable mask fragments on soil biochemical properties, enzymatic activities, and bacterial community networks. Through a 90-day incubation experiment with different mask fragment additions (0-0.1%, w/w), we observed time- and dose-dependent perturbations in soil nutrient dynamics. Specifically, NH₄⁺-N content increased significantly within the first 30 days, and soil pH rose notably after 60 days. The 0.1% treatment persistently elevated available potassium but reduced readily oxidizable organic carbon, while reducing NO₃^--N after 30 days. Soil enzyme activities exhibited obvious phase-specific responses to mask fragment stress. Urease and β-glucosidase were significantly stimulated on day 15, whereas β-glucosidase and soil respiration were significantly suppressed by day 90. Alkaline phosphatase was inhibited in the early stages, whereas catalase was activated later. Mask fragments significantly altered bacterial β-diversity and destabilized the co-occurrence network of abundant taxa. In contrast, rare taxa maintained relatively stable network structures. Mantel tests revealed that soil enzyme activities were strongly correlated with bacterial community shifts under the 0.1% treatment. However, detailed chemical characterization of mask material was not performed, and these correlations do not establish causal mechanisms. Our findings establish an empirical baseline for how the physical presence of centimeter-sized mask fragments is associated with altered soil enzyme activities, nutrient dynamics, and microbial network topology, generating testable hypotheses for future mechanistic studies to evaluate early-stage ecological risks of mask-derived waste in agricultural soils.