Interactions Of Ambrosia Trifida And Biotic Factors And The Effects On Invasion

Biological invasion has become one of the most important global environmental issues.Invasive plants have caused many problems for ecological environments,economy and society,and even human health.As global trade and scientific technology development,problems caused by plant invasion become more and more serious.It is necessary to study plant invasion mechanisms for biological invasions control.To elucidate the mechanisms underlying invasions of exotic plants,we studied their interactions with many biotic factors such as natural enemies,co-occurring native plants,and soil microbes,and analyzed the relationships between the interactions and invasion success of the invaders.The impacts of above-and below-ground enemies on invasive plants in both native and invasive regions were tested using biogeographical approach and greenhouse experiments,and the effects of soil microbes on performance of invasive and co-occurring native plants were tested from both native and invasive ranges.The influences of invasive and co-occurring native plants on soil microbial structure and function were tested using metagenomic sequencing and Biolog-ECO plane,and competitive ability comparisons of invasive species and co-occurring plants from both native and invasive ranges were tested by intra-and inter-specific competition experiments.The main results are as follows:1.Influences of enemies on invasive plants in native and invasive rangesField survey results showed that Ambrosia trifida suffered more enemy inhibitory in native range than in invasive range.Leaves and seeds of the invader were damaged much more seriously in native range.It showed A.trifida traits from native and invasive ranges were dramatically different,the population from invasive range performed higher,bigger stem diameter and more leaves and produced more seeds,and became denser in invasive range than that in native range.There was no damage by natural enemy in Solanum rostuatrm,Cenchrus panciflorus and Bidens frondosa,but A.trifida,Xanthium strumarium and Ambrosia artemisiifolia suffered damage by enemies in invasive range of Liaoning.Survey result of enemy influence in A.trifida from two ranges was an additional evidence for enemy release hypothesis(ERH),but the excat relationship between enemy release and differences in A.trifida traits is still not clear.2.Plant-soil feedbacks on Ambrosia trifida and Xanthium strumarium and their co-occurring native plantsPlant-soil feedbacks were significantly different for Ambrosia trifida in native and invasive ranges.Soil collected from native range showed negative feedback on the invader grown in greenhouse,while soil from invasive range showed netural or even positive feedback on the invader.Soil biota suppressed seed germination and growth of giant ragweed in native range,while didn’t work in giant ragweed in invasive range.In invasive range,rhizosphere soil of A.trifida showed positive or netural feedback on A.trifida but negative feedback on Siegesbeckia glabrescens in most sites;Rhizosphere soil of X.strumarium showed netural or positive feedback on X.strumarium,but netural or negative feedback on Xanthium sibiricum.Soil biota from different sources showed different effect on plant growth which could be relative to species successful invasion,and soil biota from samples invaded by exotic plants in invasive range showed positive effect on plant growth.Plant-soil feedbacks for Ambrosia trifida in native and invasive ranges also provided an additional evidence of ERH.3.Effect of invasive plants on soil microbial structure and functionThe structures of soil fungal and bacterial communities were changed by A.trifida significantly,and fungi community was affected more seriously than bacterial community.Fungi community structure of soil samples from A.trifida was significant different from that of S.glabrescens.A.trifida did not influence in fungi community diversity so much,but impacted bacteria community diversity.Compared to S.glabrescens,A.trifida decreased the metabolic ability of soil microbial community.X.strumarium also influenced in soil fungi and bacteria community,and fungi community had higher degree change than bacteria community.The microbial community was significant different from that of X.sibiricum,the invader influenced bacteria community diversity but did not work in fungi community diversity.Compare to X.sibiricum,X.strumarium increased the metabolic ability of soil microbial community.Effect of soil source was stronger than training plant on soil microbial community change which indicated invasive plant managed soil microbial community by a long term training process.4.Intra-and inter-specific competition between A.trifida plants and co-occurringnative plants from native and invasvie rangesIt showed A.trifida populations from native and invasive ranges had similar intraspecific and interspecific competition ability which indicated A.trifida did not evolve its competition in invasive range.When competed with native plants from native range,A.trifida had similar competition ability with them,and the effect on plant height,leaf number and total biomass were similar with each other;A.trifida had stronger competition ability when competed with native plants from invasive range,and suppressed total biomass of native species strongly.Species from native range had stronger competition ability than species from invasive range when competed with A.trifida from two ranges,and species from invasive range were more sensitive to competition and suffered more inhibition from A.trifida which indicated native plants had lower resistant ability to A.trifida in invasive range.In conclusion,biotic factors including enemies,co-occurring native plants,and soil microbes were important for exotic plants invasion.Biotic factors showed positive effect on A.trifida invasion,the interactions between biotic factors and invader will promote the invasion process successfully.The results supported enemy release hypothesis,and indicated weaker biotic resistant ability of native plants in invasive range,while did not support the evolution of increased competitive ability hypothesis.