The Growth And Reproduction Of Potamogeton Crispus L. Response To Global Different Warming Patterns And Eutrophication

Submerged macrophytes play an important role in maintaining the ecological function of shallow lakes.However,contemporary evidence suggest they are experiencing a global decline because of the multiple compound anthropogenic stressors impacting these vulnerable ecosystems.Two of the major,dominant drivers are eutrophication and climate change yet evidence on their interactive effect on aquatic plants is still partial and fragmented.In a future warmer climate with increasing mean temperatures,heat waves duration and intensity were also predicted to increase.On the other hand,eutrophication is still a major water quality issue for freshwater systems.Whereas most existing research has focused on effects of climate change or eutrophication on submerged macrophytes,little attention has yet been paid to the projected intensification of extreme climatic events,especially the interaction between extreme climatic events and lake eutrophication.Maternal environment can also influence life-history and offspring performance traits of aquatic plant.Therefore,understanding maternal environmental effects will contribute to predict the response mechanism of aquatic plant life-history traits to climate warming.Based on those backgrounds,we selected Potamogeton crispus L.,a widely distributed of submerged macrophytes,as monitoring object,and performed two mesocosm experiments for investigating the response strategies of submerged macrophytes to climate warming and eutrophication.Results of these studies are as follows:(1)We set three heated modes to investigate the changes in morphology,stoichiometry and early germination strategy of turions that formed in different heated modes.By analyzing the data obtained,we found that warming had no effect on turion wet weight,but extreme warming significantly increased turion length and width.The results of stoichiometry indicate that maternal extreme warming significantly increased N concentrations in turions,but C:N ratio significantly decreased.And maternal warming can accelerate the germination of turions and seedling growth to some extent.In summary,maternal warming significantly affected turion morphology,stoichiometry and germination.(2)Our experimental results indicated that warming accelerated growth and senescence of P.crispus,which suggesting a more important role in maintaining the clear water state in winter-early spring.However,lakes might be exposed to an earlier turbid-state in summer.Warming also advanced consistently the flowering phenology but had no significant effect on the duration of the flowering period.Compared to ambient temperature treatments,the first flowering date advanced by 14.7 days on average under constant warming and 17.2 days under variable warming.The peak flowering date was also advanced in the warming treatments.Although the peak flowering date delayed by 3.9 days and flowering duration appeared to be reduced slightly under P enrichment,there were no significant differences compared to control.Futhermore,the peak number of inflorescences per tank was reduced by 17 units(constant warming)or 27 units(variable warming)on average relative to that of the controls.(3)Our results also imply that warming may result in less sexual reproduction by reducing the number of infructescences,especially in the variable warming treatment.Our findings suggest that the reproductive strategies of P.crispus may be changed under predicted alternations in climate regimes However,under phosphorus enrichment may contribute to sexual reproduction by producing higher seed setting rate per infructescence,which may be beneficial for the P.crispus population responses to environment change.(4)With respect to the propagules carbon and nitrogen stoichiometry,warming and phosphorus addition resulted in change of the seeds and turions carbon and nitrogen content.Increase in mean temperature and heat waves lead to total carbon(TC)content of turions decreasing,while both warming and phosphorus addition decreased TC content of seeds.Phosphorus addition significantly decreased total nitrogen(TN)content of turions compared to the control.TN content of seeds increased in the constant warming group while decreased in the variable warming group.The C:N ratio increased in turions with phosphorus addition,however,the C:N ratio decreased in seeds because of the interaction between warming and phosphorus addition.On the other hand,the variable warming group had the higher seeds C:N ratio than the other groups.We found that the changes of sexual and asexual propagules carbon and nitrogen were complex in our study.In addition to the effect of warming and phosphorus addition,carbon and nitrogen content of the propagules may be also influenced by the other environment factors(such as sediment nutrition level).