Responses of morphological and physiological traits to herbivory by snails of three invasive and native submerged plants

3种入侵和本地沉水植物形态和生理性状对螺类牧食的响应

The submerged plant species Carolina fanwort(Cabomba caroliniana)has become a dominant invasive aquatic plant in the Lake Taihu Basin(LTB)in China.Introduced species may escape their original specialist enemies and encounter fewer enemies in their new environment.They were assumed to have suffered less herbivory than native species as they are relatively unpalatable(the enemy release hypothesis[ERH]).The objective of this study was to compare the responses of C.caroliniana with those of co-occurring native species to herbivory from native herbivores.We conducted a mesocosm experiment to record the responses of C.caroliniana and two commonly co-occurring native submerged plant counterparts,water thyme(Hydrilla verticillata)and Eurasian watermilfoil(Myriophyllum spicatum),to herbivory by two native generalist gastropod snails,Radix swinhoei and Sinotaia quadrata.Plant morphological traits(total biomass,shoot/root[S/R]biomass ratio and relative growth rate[RGR])and physiological traits(leaf total nonstructural carbohydrate[TNC],lignin,and cellulose)were recorded.The snail S.quadrata rarely influenced the plant traits of the three submerged plants.With the increasing numbers of R.swinhoei treatments,most of the plant traits of H.verticillata and M.spicatum changed,while those of C.caroliniana showed a relatively stable fluctuation.This result indicates that C.caroliniana is more resistant to herbivory by the snail R.swinhoei,which is consistent with the ERH hypothesis.This finding indicates that herbivorous snail species contributes to the invasion of C.caroliniana,which potentially alters the species composition of submerged plants in the plant community.

沉水植物水盾草(Cabomba caroliniana)已成为中国太湖流域的优势入侵水生植物。与外来物种的原产地环境相比,引入地新环境中存在的专食性天敌较少。外来物种可能会逃避其原产地环境中的天敌牧食,又因为它们的适口性相对较差,从而导致在引入地外来物种通常比本地物种遭受的牧食者影响更低(天敌逃逸假说)。本研究的目的是比较水盾草与共生的本地沉水植物对本地牧食者的响应。我们进行了一个中宇宙尺度实验,研究了水盾草和两种共生的本地沉水植物黑藻(Hydrilla verticillata)和穗花狐尾藻(Myriophyllum spicatum)对两种本地广食性腹足纲螺类萝卜螺(Radix swinhoei)和环棱螺(Sinotaia quadrata)的牧食响应。记录了它们的形态性状指标(总生物量、冠根比和相对生长率)和生理性状指标(叶片总非结构性碳、木质素和纤维素)。研究结果表明,环棱螺对3种沉水植物性状指标的影响较少。随着本地广食性螺类萝卜螺数量的增加,黑藻和穗花狐尾藻大部分植物性状发生了改变,而水盾草的植物性状表现出相对稳定的趋势。水盾草对萝卜螺的牧食更具抵抗力,这与天敌逃逸假说的假设一致。这一发现说明牧食性螺类促进了水盾草的入侵,这可能会改变沉水植物群落中的物种组成。