Effects Of Warming On Interactions Between Invasive Plant Alternanthera Philoxeroides And Native Herbivores

Climate warming plays an important role in the growth and defense of invasive plants,but little attention has been paid to the impact of climate warming between plant nutrient and defense resources,and the interactions between invasive plants and specialist and generalist herbivores.Therefore,it will have important theoretical and practical significance to explore how climate warming affects the interactions between invasive plants and native herbivores in the context of global change biology and invasive ecology.In this study,an invasive plant Alternanthera philoxeroides,which has caused serious threats to ecosystem and economy in China,and its native congener Alternanthera sessilis were selected as focal species.We tested the responses of A.philoxeroides and A.sessilis morphology,growth,nutrients and defense chemicals to warming by simulated infrared radiation heater.We also explored the effects of A.philoxeroides and A.sessilis with warming treatment on growth and development and host choice preference of the generalist Spodoptera litura and specialist Cassida piperata by Y-tube olfactory,petri dish experiments and field experiments.Moreover,we collected plant volatiles with dynamic headspace adsorption,and then identified and analyzed the volatiles by GC-MS and SIMCA principal components,respectively.The main findings are as follows:1.Effects of warming treatment on A.philoxeroides and A.sessilis growth and defenseIn terms of plant growth,warming treatment significantly increased the number of ramets of mixed A.philoxeroides and the cover degree of mixed A.sessilis.The biomass of roots by 1.28 g of potted A.sessilis was increased significantly under warming treatment,while the biomass of leaves by 1.28 g and roots by 1.33 g of potted A.philoxeroides were increased significantly under warming treatment.Regardless of warming,root/shoot ratio of potted A.philoxeroides was significantly greater than that of potted A.sessilis.For the plant primary metabolites,the nitrogen content by 1.03% in leaves of mixed A.philoxeroides was significantly reduced under warming treatment,but the ratio of C/N was increased.The nitrogen content of 0.32% in leaves of potted A.sessilis was significantly increased under warming treatment,but the C/N ratio was reduced.Warming treatment significantly reduced the starch content by 4% and total soluble sugar content by 2.19%,increased fructose content by 0.09% and sucrose content by 1.32% in leaves of mixed A.philoxeroides.The content of starch and fructose was decreased by 3.93% and 0.03% in leaves of mixed A.sessilis,while the content of sucrose,total soluble sugar and lignin was increased by 0.81%,6.04% and 2.20% respectively.Warming treatment significantly increased the lignin content by 0.1% in leaves of potted A.philoxeroides and decreased the lignin content by 0.03% of A.sessilis.As for the plant secondary metabolites,warming treatment significantly increased the total flavonoid content by 1.27ug/mg and total phenol content by 0.73% in leaves of mixed A.sessilis,but decreased the triterpenoid saponins content by 6.99mg/g and tannin content by 0.016 ug/mg in leaves of mixed A.philoxeroides.2.Effects of warming treatment of A.philoxeroides and A.sessilis on growth and development of S.litura and C.piperataRegardless of warming,the growth and development of S.litura and C.piperata were inhibited significantly by A.philoxeroides than that by A.sessilis.Compared with control treatment,A.sessilis with warming treatment had negative effects on both S.litura and C.piperata.A.philoxeroides with warming treatment only had negative effects on the generalist S.litura,but had no effect on the specialist C.piperata.3.Effects of warming treatment of A.philoxeroides and A.sessilis on host selection of S.litura and C.piperataWith ambient treatment,the attraction of S.litura and C.piperata to A.sessilis was stronger than that of A.philoxeroides,but the warming treatment eliminates this difference.Regardless of warming,S.litura preferred to oviposit on A.sessilis other than A.philoxeroides.Compared with control treatment,the oviposition preference index of S.litura on A.sessilis and A.philoxeroides were significantly decreased under warming treatment.The plant volatiles released from A.philoxeroides were significantly different with its native congener A.sessilis,and the plant volatiles between A.philoxeroides and A.sessilis were significantly changed as well under warming treatment.In summary,compared with A.sessilis,the biomass of invasive plant A.philoxeroides was significantly increased,and the content of nutrients decreased by warming treatment.These changes reduced the survival rate and oviposition preference of the generalist S.litura on A.philoxeroides,Adverse effects on generalist herbivores.As a result,our study suggest that global warming could promote A.philoxeroides invasion by changing the interactions between plants and herbivores.