Differences In Plant-Soil Feedbacks In The Invasive Plant Xanthium Strumarium And Its Two Phylogenetically Related Native Plants Grown Under Ambient And Doubled Atmospheric CO₂ Concentration

The effect of elevated atmospheric CO₂ on invasions of introduced plants is one of the hotspots in invasion ecology.However,most studies have focused on aboveground parts of invaded ecosystems,and little effort has been taken on soils especially on soil biota.Soil biota especially soil microorganisms and nematodes is important for ecosystem nutrient cycling,and in turn affect plant performance.With intensification of biological invasion and global climate change,more studies are needed to put insight into mechanisms of soil biota for exotic plant invasions under global change.We selected one invasive species Xanthium strumarium L.and two native species X.sibiricum Patrin ex Widder and Bidens biternata?Lour.?Merr.et Sherf f.and compared feedback effects of cultivated soils by the three species on their seedling growth and seed germination rate under ambient and doubled atmospheric CO₂ concentrations.To fulfill this purpose,we first cultivated soils by each of the three species during one or consecutive two years.Then,the cultivated soils were treated by sterilizing nematodes,microorganisms?bacteria and fungus?and total soil biota,respectively and the non-sterilizing was as the control.Seedling growth and seed germination rates of X.strumarium,X.sibiricum,and B.biternata in these soils were measured for calculating feedback effects.In conclusion,the soil grew by Xanthium strumarium in ambient condition had a stronger inhibition effect on Xanthium sibiricum growth than it worked to itself,otherwise the soil grew by Xanthium sibiricum had no effect at all which would worked for Xanthium strumarium invasion.The Xanthium strumarium soil positive feedback on Xanthium sibiricum in ambient condition was stronger than that in double CO₂ concentration and the feedback would be weaker over time.Xanthium sibiricum soil had a stronger feedback on Xanthium strumarium growth in double CO₂ concentration than that in ambient condition,and the feedback became weaker over time.But the negative feedback did not work to itself in ambient condition,while became stronger as the time processed.The soil from Bidens biternata had no effect on Xanthium strumarium growth and germination in both CO₂ concentration treatments.