不同程度南方菟丝子寄生对入侵植物三叶鬼针草生长的影响

生物入侵严重影响了生态系统的结构和功能。菟丝子属植物可以有效地抑制入侵植物的生长，恢复本地群落，是一种有效的生物防治剂。本文以本地寄生植物南方菟丝子（Cuscuta australis）和三叶鬼针草（Bidens pilosa L.）为研究对象，采用不同数量的南方菟丝子茎段（长度15cm）寄生入侵植物三叶鬼针草来形成不同的寄生程度（寄生I、II、III分别由1、2、3段南方菟丝子茎段寄生），分析不同程度的寄生对寄主三叶鬼针草补生长的影响，并探讨寄生植物对寄主补偿生长的诱导。南方菟丝子寄生34d之后，三种程度的寄生均可显著抑制三叶鬼针草生长。寄生III处理组的南方菟丝子生物量显著大于寄生I和寄生Ⅱ处理组。不同寄生强度对三叶鬼针草生长的影响具有一定的差异。寄生II和寄生III的三叶鬼针草叶生物量、茎生物量、地上生物量、地下生物量、总生物量、株高与冠幅均显著低于寄生I，但相互之间不存在显著性差异；寄生II的三叶鬼针草的叶面积、根长和根体积均显著低于寄生I，寄生III的叶面积和根长高于寄生II，但与寄生I及寄生II之间不存显著性差异，寄生III的根体积显著高于寄生II，但与寄生I之间不存在显著性关异。与对照相比，不同程度寄生下三叶鬼针草的NAR和RGR极显著降低。寄生II的三叶鬼针草的RGR显著低于寄生I，寄生III的三叶鬼针草的RGR高于寄生II，但与寄生I及寄生II之间均不存在显著性差异。寄生II与寄生III的三叶鬼针草的NAR显著低于寄生I组，但相互之间不存在显著性差异。除寄生I处理组外，寄生II与寄生III处理导致三叶鬼针草与南方菟丝子的累积生物量均显著低于对照。寄生II处理组的累积生物量要低于寄生I处理组，寄生III处理组的累积生物量要高于寄生II处理组，但显著低于对照组，表明寄生III处理组的三叶鬼针草产生了低补偿生长。由于南方菟丝子寄生显著抑制入侵植物的生物量，因此南方菟丝子仍具有防治入侵植物的潜力。

Effect of differing levels parasitism from native Cuscuta australis on invasive Bidens pilosa growth

Biological invasions have severe impacts on the composition and function of natural ecosystems.Biological control may be a potential method to effectively control invasive species,especially using the native biocontrol agents.Cusuta spp.species are parasitic plants and were verified as potential biological control agents.Bidens pilosa L.(Compositae),an annual forb native to South America,commonly invaded subtropical south-western China.C.australis(Convolvulaceae),native to China,is a holoparasitic plant.Here we aimed to find out whether Cuscuta spp.species are verified as potential effective biocontrol agents on the invasive plant Bidens pilosa or alternatively and whether they induce compensatory growth in B.pilosa by testing the effects of differing levels of parasitism from the native parasitic C.australis with invasive B.pilosa.B.pilosa parasitized by one,two and three sections of C.australis stem with 15 cm length were taken as parasitism intensity at Ⅰ,Ⅱ and Ⅲ level,respectively.Parasitism by C.australis significantly decreased B.pilosa growth.The biomass of parasitic C.australis at the highest level(Ⅲ) was significantly higher than those at the two lowest levels(Ⅰ and Ⅱ).The above-ground biomass,below-ground biomass,total biomass,height and canopy diameter of B.pilosa parasitized by C.australis at the two highest parasitism levels(Ⅱ and Ⅲ) were significantly lower that those at the lowestI level of parasitism(Ⅰ).The leaf area,root length and root volume of B.pilosa at Ⅱ level were significantly lower than those at Ⅰ level,while the root volume at Ⅲ level were significant higher than those at Ⅱ level.In addition,parasitism by C.australis significantly decreased the relative growth rate(RGR) and net assimilation rate(NAR) of B.pilosa.RGR of B.pilosa at the highest level(Ⅲ) were higher than that at the second highest level(Ⅱ) without statistical significance.The cumulative biomass of B.pilosa parasitized by C.australis at the highest parasitism(Ⅲ) was significantly higher than at the second highest parasitism(Ⅱ),which was closed to that at the lowest parasitism level(Ⅰ) but still lower than that in the control.This suggested an undercompensatory growth strategy of B.pilosa parasitized by C.australis at the highest parasitism level(Ⅲ).Thus,the native parasitic C.australis could be used as a potential biocontrol agent to control invasive B.pilosa.But the optimal intensity of parasitism is important and necessary if biological control is to be effective.