| Reproduction is a core issue in plant life history and evolution.Successful reproduction and survival is the key to competitive advantage of plants in specific habitats.Many plants have both sexual and asexual reproduction modes.Due to general resource limitations,resource allocation between the two reproduction modes often shows trade-offs in order to maximize fitness.Many previous studies have shown that external physical or biological environments cause different patterns of sexual and asexual reproduction.However,this does not prove that there is direct resource competition between them.Therefore,to avoid complex influences triggered by environmental factors,direct control of sexual reproduction and responses of asexual reproduction should be employed,focusing on the direct resource tradeoff between them.Using Sagittaria trifolia as the research material,this study took advantage of the same genotype of clone strains and applied pollen quantity and quality treatments to plants of the same genotype composition.Pollen quantity treatments included none pollination,half pollination and full pollination,while quality referred to selfing,outcrossing,and half selfing and half outcrossing.Under such pollination treatments,the output of sexual reproduction was quantified,and the effects on the resource input of asexual reproduction were measured.Under the control of pollination quantity,the results showed that fruit-set,total fruit number and total seed number of full pollination treatment were significantly higher than those of half pollination treatment,and the level of sexual reproduction of half pollination was significantly higher than that of none pollination treatment.In terms of asexual output,on the contrary,the total number of corms,the total corm weight and the number of emerging seedlings in the none pollination treatment were significantly higher than those in the half pollination and full pollination treatments.Yet the emergence rates of corms under each treatment were not different.This suggests that there is direct resource competition between sexual and asexual reproduction under pollination quantity control.Under the quality control of pollination,the fruit-set in selfing treatment was significantly higher than that of outcrossing treatment,leading to a higher trend of total fruit number and total seed number.Consequently,the total corm weight and number of emerging seedlings in outcrossing treatment tended to be greater than selfing.Half selfing and half outcrossing treatment was at the intermediate level of the two treatments with regard to both sexual and asexual reproduction.Similarly to quantity control,there was still no difference in the emergence rate of corms among quality treatments.This suggests that resource trade-off is also present between sexual and asexual reproduction under pollen quality control.In addition,there were significant differences in sexual and asexual reproductive levels of plants from different population sources,indicating that geographical environments among populations might have resulted in local adaptation in genotypes of specific populations.The responses to pollination of different population sources also varied considerably,which highlights phenotypic plasticity of Sagittaria trifolia,the ability of changing phenotypic traits to heterogeneous environments.In this study,the direct control of sexual reproduction was achieved by varying degrees of pollination control of Sagittaria trifolia,thus revealing the direct resource trade-off between sexual and asexual reproduction.This implies that in agricultural practices,plant life functions with resource tradeoffs can be artificially promoted or inhibited according to actual demand to maximize production.Furthermore,it is helpful to predict phenotypic responses of plant populations in the case of global change with more and more severe pollen limitation scenarios,which provides theoretical basis for species conservation and utilization. |
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