Cropping Patterns Shape Soil-Dwelling Nematode Communities in the Mekong Delta Paddy Fields

Rice intensification influences soil biodiversity and ecological functioning in paddy ecosystems; however, its effects on soil nematode communities across different rice production systems remain poorly understood in the Vietnamese Mekong Delta (MD). This study evaluated the effects of rice cropping practices in the MD on nematode community composition, trophic structure, functional guilds, diversity, plant-parasitic nematodes (PPN), and soil chemical properties. A total of 91 soil samples were collected from double-rice intensive (RR), triple-rice intensive (RRR), and rice–upland–rice rotational (RUR) systems. Thirty nematode genera were identified, with a total abundance showing high variability, but no significant differences among cropping systems. Community composition differed considerably among systems, with Chronogaster dominating across all systems, particularly under RRR, whereas RUR supported more dominant genera with higher abundances of Tyleptus, Mesodorylaimus, Cephalobus, and Calolaimus. RUR exhibited significantly greater genus richness, and higher abundances of fungivores, omnivores, and higher colonizer–persister groups (cp4–cp5), indicating greater soil food-web complexity and ecological stability. In contrast, RRR was characterized by bacterivore-dominated communities, and increased abundance of cp3 nematodes, suggesting simplified community structures associated with agricultural intensification. Plant-parasitic nematodes remained relatively stable across management systems, despite taxon-specific responses. Soil pH, organic matter, and nitrogen availability were strongly associated with nematode community variation. Therefore, crop diversification through rotational practices enhanced belowground biodiversity, and promoted more sustainable soil ecological functioning in intensive rice production systems.