| Every stage of plants' life cycle is affected by temperature.Temperature affects photosynthetic efficiency,growth rate,flowering phenology and growth period directly,and affects vegetative and reproductive development of plants by changing soil nutrient and water indirectly.Climate change,typically characterized by global warming,has made profound impacts on species diversity,community structure and even on global ecosystems.Plants in the Qinghai-Tibet Plateau are of foresight and foreseeability to warming.Warming may change flowering phenology,floral characteristics,pollination characteristics and reproductive allocation of plants and ultimately affect reproductive success of plants.To explore the growth and reproduction of forb species and their adaption to warming,we chose ten typical forb species distinguished according their flower diameters focuing the effects of warming on reproductive allocation.Besides,Polygonum viviparaum with both sexual reproduction and asexual reproduction was chose to study the effects of warming on trade-off relationships of resource allocation and reproduction methods.In addition,Delphinium caeruleum has special floral characteristics with nectar robbing.We tested how changes of floral characteristics and the interaction of plants and pollinators might affect pollinator species,pollination efficiency and reproductive success after warming.The main results are as follows:1.Effects of experimental warming on the reproductive allocation of ten forb species.(1)With the increase of warming levels,responses of individual reproductive characteristics of the same species were consistent.(2)Plant height of ten species increased with the increase of warming levels.(3)Responses of different plants to warming were quite different.Number and dry weight of flowers,dry weight of stem and leaves,above-ground biomass of plants in group S with smaller flowers increased with the increase of warming levels,while the above characteristics of plants in group L with larger flowers had opposite respones.(4)Reproductive allocation of ten species decreased with the increase of warming levels.More resources were invested in vegetative development and the investment to reproductive development was reduced.2.Effects of experimental warming on growth and reproduction of P.viviparaum in the Qinghai-Tibet Plateau.(1)Experimental warming promoted both vegetative development and reproductive development of P.viviparaum,but there was a significant trade-off relationship between them.Under warming,more available resources of P.viviparaum were devoted to vegetative development,resulting in increase of plant height,leaf number,dry weight of stem and leaves and decrease of reproductive allocation.(2)The length of sexual spike,number and dry weight of flowers per spike decreased after warming while number and dry weight of bulbils per spike increased,indicating more investment to asexual reproduction.The low proportion of sexual reproduction is mainly due to the lack of efficient pollinators and high abortion rate of pollen grains and ovules.Therefore,asexual reproduction yields higher than sexual reproduction.(3)Pollen number and germination rate were not affected by warming treatments.3.Ecological effects of experimental warming on D.caeruleum.(1)Flowering phenology of D.caeruleumime was advanced and plant height was increased after warming.(2)After warming,the blooming period and floral longevity of D.caeruleum was shorted and flower diameter was reduced.(3)After warming the length of nectar spurs were shorted and nectar volume was reduced,which resulted in shorter duration of single visit,less pollen deposition of single visit and decreased pollination efficiency of D.caeruleum.(4)Decreased pollen viability of D.caeruleum after warming together with the effects of changed phenology,shorted floral longevity and decreased pollination efficiency led to lower seed-set rate.(5)Dry weight of flowers decreased while dry weight of stem and leaves increased after warming.D.caeruleum devoted more resource to vegetative development,but relatively reduced investment to reproductive development leading to lower reproductive allocation after warming. |
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