It is well known that crop monoculture can induce negative effects on soil ecosystems and crop productivity. However, little is known about how vegetable monoculture affects the soil nematode community structure and its relationship with vegetable yields. In this study, the composition, abundance, metabolic footprint, and ecological indices of soil nematodes are investigated in monocultures of pumpkin and melon. The relationships between nematode community structure and yields of pumpkin and melon were analyzed by linear regression. Both monoculture soils of pumpkin and melon suppressed the relative abundance of bacterivores but increased the relative abundance of plant parasites. Pumpkin monoculture soils decreased soil nematode diversity but increased the maturity index of plant parasites. Monoculture soils of pumpkin and melon decreased the metabolic footprint of lower- and higher-level trophic groups of the soil food web, respectively. Pumpkin and melon monoculture soils increased the food web indices channel index (CI) but decreased the enrichment index (EI) and the structure index (SI). The monoculture soils of pumpkin and melon led to a more fungal-dominated decomposition pathway and degraded soil food web conditions. The abundance of bacterivores and food web indices EI and SI were positively correlated with soil nutrients and pH, while the abundance of plant parasites and CI were negatively correlated with soil nutrients and pH. Paratylenchus was negatively correlated with pumpkin and melon yields and could be the potential plant parasites threatening pumpkin and melon productions. Redundancy analysis showed that monocultures of pumpkin and melon altered the soil nematode community via soil properties; total N, total P, alkeline-N, and pH were the main driving factors.

In this study, the effects of different modifiers on rhizosphere soil microorganisms, their functions, and the soil properties of continuous tomato cropping were investigated. Nine amendments were selected to treat the soil from a 14-year continuous tomato cropping system. Tomato yield, soluble solids, soil physical and chemical properties, and soil enzyme activities were measured. Changes in soil microbial community structure and function were determined by metagenomic sequencing, and their correlation with environmental factors was analyzed. The results showed that among the nine amendments, the combination of farmyard manure + Bacillus subtilis + Trichoderma harzianum (T2) and plant-derived straw decomposed soil + Bacillus subtilis + Trichoderma harzianum (T3) had the most significant effects. The tomato yield, soil hydrolyzable nitrogen, available phosphorus, available potassium, organic matter, and total nitrogen contents and soil phosphatase activities were significantly increased under the T2 and T3 treatments. Compared with the CK treated with T2, the contents of yield, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, organic matter, and total nitrogen were significantly increased by 34.46%, 41.84%, 52.44%, 45.01%, 24.5%, and 41.18%, respectively. The soil microbial community structure also changed significantly. The relative abundance of Proteobacteria, Chloroflexi, and Bacteroidota increased significantly. The relative abundance of Hyphomicrobium, Rhodomicrobium, and Rhodoplanes increased significantly compared with the control. The soil microbial function was mainly enriched in two pathways of amino acid metabolism and carbohydrate metabolism. Among them, T2 significantly enriched six community functions, such as bacterial chemotaxis. T3 significantly enriched three community functions, such as glutathione metabolism. A correlation analysis showed that soil hydrolyzable nitrogen, available phosphorus, pH, phosphatase, and catalase were the key factors affecting microbial community changes. The treatment of farm manure/plant-derived straw decomposed soil + Bacillus subtilis + Trichoderma harziensis improved the soil environment, increased crop yield, clarified the effects of different modifiers on the functional mechanisms of the soil microbial community, and provided a practical solution to the problem of soil degradation in agriculture monoculture.

Acidified soils in greenhouse vegetable systems constrain crop production and soil ecological functions. This study investigated the effects of different amendment treatments on soil ecological factors in acidified soils under greenhouse spinach cultivation in Baoqing County, China. Three treatments were established: farmyard manure alone (T1), Haijuneng soil amendment, an alkaline oyster-shell-based soil conditioner, alone (T2), and the combined application of farmyard manure and Haijuneng soil amendment (T3). High-throughput sequencing of the 16S rRNA gene combined with functional prediction was used to analyze soil bacterial community characteristics and their relationships with soil physicochemical properties and enzyme activities. The results showed that soil pH increased significantly under T2 compared with T1 (4.59 vs. 4.14), along with higher exchangeable calcium (16.11 vs. 12.20 cmol kg⁻¹) and exchangeable magnesium (5.54 vs. 3.83 cmol kg⁻¹). In contrast, T3 showed the highest organic matter content (48.54 g kg⁻¹) and phosphatase activity. Compared with T1, both T2 and T3 increased urease activity and altered bacterial community structure and functional composition, while microbial diversity was highest under T2. Soil pH and available phosphorus were the main factors driving bacterial community variation, whereas pH, exchangeable calcium, and exchangeable magnesium were significantly correlated with multiple dominant genera and KEGG level 2 pathways. Overall, the amendment strategies showed distinct effects: compared with the conventional practice of farmyard manure alone, Haijuneng soil amendment alone was more effective in partially alleviating soil acidification, whereas its combined application with farmyard manure was more favorable for soil organic matter accumulation and enhancing soil phosphorus supply potential.