Impact of land use type and organic farming on the abundance, diversity, community composition and functional properties of soil nematode communities in vegetable farming

The excessive application of chemical fertilizers in intensively managed agricultural fields worldwide has resulted in soil degradation and biodiversity loss. This has contributed to a growing interest in sustainable management, such as organic farming. Until now, studies addressing the impact of conventional and organic management on soil biodiversity and functioning have mainly focused on arable farming and only a few reports are available on vegetable production. Vegetable farming is of particular interest, since management intensity is usually very high and there is an increasing demand for vegetable products. Soil nematodes are useful indicators of management intensity on soil ecosystem functioning because they occupy several trophic levels in soil micro-food webs and play a crucial role in nutrient cycling, pest suppression, and the regulation of microbial communities. In this study, we assessed the impact of management intensity and farming system on the community structure and functional guilds of soil nematodes, comparing 20 conventional vegetable fields, 20 organic vegetable fields, and 20 extensive grasslands in Switzerland, analyzing over 30’000 nematode individuals and detecting 98 different nematode genera. We found significant differences in the community structure and functional composition across three farming systems. Extensive grasslands contained the highest nematode abundance, followed by organic vegetable fields, and conventional vegetable fields, indicating a decline due to land-use intensification. Organic farming led to a significant increase in the abundance of herbivores (+82%), bacterivores (+206%) and omnivores (+135%) in comparison with conventional farming. Organic management also enhanced composite (+195%) and herbivores (+451%) footprints, suggesting greater carbon and energy enrichment in soil food web through these functional groups. Community composition of soil nematodes varied significantly across the three farming systems, with each farming system fostering specific indicator taxa. In conclusion, our results show that farming system has a major impact on soil nematode communities with increasing nematode populations under organic vegetable farming. Although organic vegetable production may benefit from enhanced soil fertility due to increased population densities of microbe feeding and omnivorous nematodes, the threat from plant parasitic nematodes to vegetable production requires attention and control strategies should be developed further