Soil biota, but not soil nutrients, facilitate the invasion of Bidens pilosa relative to a native species Saussurea deltoidea

摘要

Existing evidence has shown that soil biota and nutrient availability in the introduced ranges are drivers of plant invasions. Bidens pilosa, an invasive species, grows better in rich soil from under shrubs than in poor soil from spaces between the shrubs. Here, we hypothesise that soil biota will benefit B. pilosa more than the native herb Saussurea deltoidea and that B. pilosa will also be favoured over S. deltoidea in nutrient-rich soil compared with soil lower in nutrients. To test both hypotheses, we conducted an experiment in which B. pilosa and S. deltoidea were subjected to non-sterile and sterile soils from both shrubs and gaps. Sterilisation had greater negative effects on the growth of B. pilosa than S. deltoidea indicating that mutualists appear to have stronger effects on the invasive than on the native plant. Although shrub soil was significantly richer in nutrients than gap soil, this difference did not affect biomass production of B. pilosa. In contrast, B. pilosa had greater total biomass in non-sterile shrub soil than in non-sterile gap soil. These findings suggest that successful invasions of B. pilosa are because of the shrub-dependent effect of soil biota in the introduced ranges and that its habitat association appears to be closely linked to soil biota, but not soil nutrients.