The Effect Of The Invasive Plant Phytolacca Americana On The Native Plant P.Acinosa And The Native Herbivorous Insect Spodoptera Litura And Its Mechanism

Biological invasion has always been a serious topic,invasive organisms will have a series of effects on the local ecosystum.The invasive plant Phytolacca americana is native to North America and escaped after being introduced in 1935,as its population continues to expand,it became an invasive plant.However,the research on P.americana mostly focused on its accumulation of heavy metals,but is harm as an invasive plant,especially its impact on native plants and native herbivorous insects are little known.In this experiment,the invasive plant P.americana,the local plant P.acinosa,the exotic non-invasive plant P.icosandra,and the native herbivorous insect Spodoptera litura were studied to explore the influence of the invasive plant P.americana on the native plant P.acinosa and the native herbivore S.litura and its mechanism,provide a certain theoretical basis for the evaluation of the invasive plant P.americana.The main findings are as follows:1.The influence of P.americana on P.acinosaIn the control group,the Competitive Balance Index(CBI)between P.acinosa and P.americana is significantly greater than 0(P=0.0031),indicated that P.americana has great competitiveness;The Relative Yield Total(RYT)of P.acinosa and P.americana is not significant compared to 1(P=0.5581),indicated that P.acinosa and P.americana need the same resources,and one species can exclude another species through competition;The Relative Yield(RY)of P.americana is significantly grcater than 1(P=0.0327),it shows that the interspecific competition of P.americana and P.acinosa is less than the intraspecific competition of P.americana.However,under the conditions of spraying insecticides and fungicides at the same time,the RY of P.americana is not significant compared with 1(P=0.061),it indicated that the interspecific competition of P.americana and intraspecific competition between P.acinosa and P.americana equal competition;The RYT of P.acinosa and P.americana is not significant compared to 1(P=0.071),indecated that the contest competition between P.acinosa and P.americana.The CBI betweea P.acinosa and P.americana is not significant compared to 0(P=0.851),indicating that P.acinosa and P.americanaare comparable in competitiveness.This also shows that P.americana is more resistant to insects and bacterial properties.Whether to spray insecticides and fungicides has little effect on P.americana.When P.acinosa and P.americana are mixed(P.acinosa-P.americana),compared with single planting(P.acinosa-P.acinosa),the chlorophyll content of P.acinosa is significantly reduced,and the above-ground biomass is also significantly reduced,growth of P.acinosa is inhibited.But on the whole,the above-ground biomass of P.acinosa is significantly larger than that of P.americana,while the underground biomass and root-shoot ratio are significantly less than that of P.americana,which shows the difference in resource allocation between the two.In addition,the number of racemes in the single planting of P.acinosa was more than that of the two mixed species,indicating that the reproductive traits of P.acinosa were suppressed after being mixed with P.americana.P.americana not only affected the growth of P.acinosa but also affected the reproduction of P.acinosa.2.The effect of P.americana on S.lituraIn addition to effecting the native plant P.acinosa,P.americana also affects the native herbivorous insect S.litura.From the perspective of growth and development,the larvae of S.litura fed on the leaves of P.americana are relatively small,and the first and second generations show the similar result.In addition,the S.litura fed on P.americana showed that the weight of the second generation larvae was smaller than that of the first generation.And the S.litura fed on P.americana prolonged the development period(P=0.0147),which made the S.litura increased the chance of exposure to natural enemies.In terms of physiology of the S.litura,compared with P.icosandra,and the S.litura reduced the total protein content and increased the acetylcholinesterase(AChE)and glutathione-S-transferase(GST)enzyme activities after feeding on P.americana.From the perspective of reproduction,the number of eggs laid by S.litura after feeding on P.americana leaves decreased.In the selective experiment,from the point of view of Oviposition Preference Index(OPI),S.litura also prefers to lay eggs on plant P.icosandra(P=0.0103).In order to reveal the influence mechanism of P.americana on the growth and reproduction of S.litura,the secondary metabolites and nutrient content of P.americana and P.icosandra were measured.The results show that the content of lignin and total flavonoids of P.americana is significantly higher than that of P.icosandra,but the tannin content and total phenol content are relatively low.In terms of nutrient content,the soluble sugar content of P.americana is significantly higher than that of P.icosandra,but the starch content is relatively low.