Effects of the invasive common milkweed (Asclepias syriaca) on nematode communities in natural grasslands

Abstract

Summary Thousands of plant species have been introduced, both deliberately and accidentally, to native ecosystems across the globe. The common milkweed, Asclepias syriaca, is an invasive fast-growing plant species that has invaded natural and managed areas in Europe in recent years. However, only a few studies have investigated its impacts on above-ground and below-ground native biota. Soil nematodes are considered to be the most abundant metazoans, comprising different trophic groups. We examined soil nematode populations on several independent sites invaded and non-invaded by A. syriaca in southern Slovak Republic. We hypothesised that alteration of above-ground nutrient sources caused by invasion would alter nematode abundance, species diversity and trophic structure. Our study revealed that the nematode communities were not negatively affected by A. syriaca invasion over a period of two vegetation seasons. The most surprising results were that common milkweed did not decrease the abundance of plant parasites, bacterivores or fungivores and did not affect species diversity. Moreover, basic physicochemical soil parameters were similar in both invaded and non-invaded sites, although there is evidence that invasive milkweed considerably decreases native plant species cover. It is thus reasonable to conclude that A. syriaca does not pose a threat to soil nematode communities but has a negative impact on native plants. As there is an absence of nematological studies from A. syriaca-invaded ecosystems and considering it has invaded a wide range of habitats, it is impossible to generalise our findings and further studies are required.