Effects Of Reproductive Strategies And Environmental Stresses On Reproductive Allocation Of Invasive Plants

Resource allocation is often influenced by plant reproductive modes,life history characteristics and resource environment.Optimal resource allocation of invasive plants,especially to reproductive parts,may facilitate their adaptation and spread in the introduced range.Thus,studies on the reproductive strategies are critical to understanding the invasive mechanisms of exotic plants.In this study,we examined the resource allocation to reproductive part of invasive plants species with different reproductive modes(sexual reproduction and/or clonal reproduction)and life histories(life span and reproductive frequency in life).The study systems included Triadica sebifera,Alternanthera philoxeroides,Phytolacca americana,Bidens alba and Talinum paniculatum.(1)To investigate the seed variations in physical and chemical traits of T.sebifera(perennial tree)and these effects on seed germination,we measured the physical(size,hardness,seed coat thickness)and chemical(soluble protein,sugar,sugar,gibberellic and abscisic acid)properties of seeds of 12 populations from native China and 12 populations from invasive range US,and tested their germination rates and timing in a greenhouse experiment.The results showed that seeds from the invasive range were larger,had higher gibberellic acid concentrations and ratio of gibberellic acid to abscisic acid,while had lower crude fat compared to those from the native range.There was no difference about other properties between two ranges,which included seed mass,coat thickness,soluble protein and sugar.And more importantly,seeds from the invasive range germinated faster than those from the native range.Our results suggest that larger seeds and higher GA are likely to contribute to faster germination,potentially facilitating T.sebifera invasion in the introduced range.(2)To examine die resource allocation of Alternanthera philoxeroides(perennial clonal herbs)in heterogeneous habitats,we investigated the abovegroxmd biomass,inflorescence number and soil nutrition in aquatic and terrestrial habitats.Furthermore,we tested the effects of nutrition,density and water on the allocation of sexual reproduction of Aphiloxeroides in a common garden experiment.The results showed that plants of A.philoxeroides in aquatic habitats produced more inflorescences and had a higher proportion of inflorescence with monoecious flowers than those in terrestrial habitats.Soil nutrients(total nitrogen and total carbon)in aquatic habitats were significantly higher than those in terrestrial habitats.The results of common garden experiments showed that nutrients addition,higher of initial plant density and water treatment significantly increased the output of inflorescence of A.philoxeroides and the biomass allocation to sexual reproduction.Our results indicated that in higher resource environment like aquatic habitat,A.philoxeroides will invest more biomass to sexual reproduction.(3)To examine the effects of nutrition on the resource allocation of Bidens alba(an annual seed herb),Talinum paniculatum(a perennial herb with mixed reproductive modes),Phytolacca americana(a perennial herb with mixed reproductive modes)and A,philoxeroides(perennial clonal herb),we conducted a common garden experiment with different nutrition applications.The results showed that nutrition significantly promoted the growth of all invasive plants species.Plant allocated more biomass to shoot under higher nutrient level and then more biomass to sexual reproduction.Therefore,the resource allocation of those invasive plants were consistent with the prediction of optimal partitioning theory.(4)To examine the interactive effect of nutrition and temperature on the resource allocation of A.philoxeroides and R Americana,we conducted another experiment with different nutrition applications and different temperatures.The results showed that the high temperature decreased the plant growth and reduced the allocation to sexual reproduction,while the addition of nutrient could promote the plant growth and increased the investment to sexual reproduction.Our results implied nutrition is the one of major factors affecting resources allocation of invasive plant.(5)To examine the effects of herbivory and/or competition on the inflorescence of A philoxeroides,we conducted a common garden experiment with neighboring native plant A.sessilis,and two herbivory treatments of Agasicles hygrophila and Cassida piperata.The results showed that competition and/or herbivory could significantly reduce the inflorescence number of A.philoxeroides.However,herbivory had no significant effect on the sex investment ratio.We also investigated the effects of heavy herbivory on the growth and reproduction of T paniculatum.The results showed that heavy herbivory could significantly inhibit plant growth and reduced sexual reproduction,but herbivory from aboveground could increase the root.shoot ratio of plants.Overall,invasive populations of invasive plants have adaptive evolution under novel selective pressures.Moreover,resource allocation of invasive plant is affected by nutrition and it was consistent with optimal partitioning theory.Therefore,adaptation in reproductive strategies and resource allocation to reproduction may enhance the invasiveness of exotic plants.