Effects Of Warming And Insect Damaging On Floral Syndrome,Pollinator Visiting Behavior And Reproductive Success Of Impatiens Oxyanthera

Climate warming threatens the plant-pollinator mutualisms and leads to a pollination crisis.At the same time,climate warming induces pest outbreaks.However,the effects of climate warming and insect pests on plant-pollinator interactions and their mechanisms are still unclear.Therefore,Impatiens oxyanthera Hook.f.,a perennial herb endemic to China,was taken as the research object.Floral syndrome,the content of defense substances,pollination behaviors and efficiency of pollinators and plant reproductive success in responses to herbivorous insects were explored under warming through simulated warming in different ways(simulated warming by infrared heater in2020 and by transplanting to lower altitude in 2021)and the same damaging treatment(the control,mechanical damaging and damaging by larvas of Spodoptera litura Fabricius).The study object was to uncover the influence mechanism of global warming and insect pests on plant-pollinator interactions,and to provide references for the introduction and cultivation of wild Impatiens species under climate warming.The main results were as follows:1.Effects of warming and insect damaging on flowering phenology of I.oxyanthera Warming and insect damaging had no significant effect on the flowering duration and the lifespan of single flower in I.oxyanthera.However,the flower bud stage was significantly affected by warming,which shortened the flower bud stage by 20.52%.2.Effects of warming and insect damaging on floral syndrome of I.oxyantheraIn 2020,warming significantly reduced the length of corolla tube and nectar spur of I.oxyanthera,but insect damaging had no significant effect on flower size.On the contrary,the flower temperature of insect damaging treatment was significantly higher than the corresponding value of the control,but the effect of warming on flower temperature was not significant.Pollen viability was significantly affected by damaging treatment,and pollen viability of insect damaging treatment was significantly higher than that of the control treatment.The pollen number per flower and total flower number per plant were significantly affected by elevated temperatures through transplanting to lower altitude,which showed that the pollen number at lower altitude was lower than those at middle and high altitudes.Neither warming nor insect feeding had significant effects on nectar volume,but at low altitude,nectar fructose concentration and sucrose concentration were significantly lower than those of the control when the leaves were damaged.The diversity of nectar-dwelling bacteria and fungi was as follows: middle altitude > low and high altitude.At low and high altitudes,endemic nectar-dwelling bacteria under mechanical and insect damage were more than that under the control treatment.However,lefse(LDA Effect Size)analysis showed that at the genus level,there were more unique genera of bacteria in the nectar of I.oxyanthera at middle altitude,while there was no significant difference in fungi among all experimental treatments.3.Effects of warming and insect damaging on defense compound content and C/N ratio of I.oxyantheraWarming significantly increased the content of condensed tannins and total phenols in stems,while insect damaging increased the content of condensed tannins and total phenolsin in flowers.Warming increased the C/N ratio of leaves and reduced the C/N ratio of stems and flowers when the leaves were damaged.4.Effects of warming and insect damaging on Pollinator’s visiting behavior and pollination efficiencyOnly under the control,the visiting frequency of pollinators under warming treatment was significantly higher than that under the unwarming treatment.Visit frequency of pollinators,residence time on single flower and the ratio of pollen removal was as follows in order: high altitude > medium altitude > low altitude.The effects of elevated temperatures and insect damaging on pollen deposition of I.oxyanthera were not significant.5.Effects of warming and insect damaging on Female reproductive success of I.oxyantheraThe fruit setting rate per plant was not significantly affected by temperature increase and insect damaging in 2020,while the fruit setting rate per plant was as follows in order: high altitude > medium altitude > low altitude in 2021.The results of two-year experiment showed that there was no significant difference in fruit setting rate between different treatments.In conclusion,warming accelerated flowering,reduced floret size,flower number per plant,pollen number per flower and the diversity of nectar-dwelling microorganisms,thus decreased pollinator attraction,the ratio of pollen removal and fruit setting rate.However,insect damaging significantly increased flower temperature and pollen viability,decreased fructose and sucrose concentration of nectar,the diversity of nectar fungi and Bacteria and the ratio of pollen removal,and had no significant effect on pollinator’s visit behavior and pollen deposition,so it had no significant effect on fruit setting rate and seed setting rate.Therefore,although warming and insect damaging have changed the floral syndrome and have certain influence on pollinator attraction,their influences on reproductive success is neutral.