| Manipulative experiments and space-time alternative warming experiment are two general ways of warming experiment.Warming has a significant impact on important processes of ecosystem(such as litter decomposition).We compared the decomposition characteristics of four wetland plants(Zizania caduciflora 、 Schoenoplectus tabernaemontani 、 Sparganium stoloniferum 、 Hippuris vulgaris)litter under manipulative control in situ decomposition experiment and large-scale space natural warming experiment.Among them,the manipulative controlled in-situ decomposition experiment is mainly realized in Napahai Wetland by means of open top warming chembers(OTC),while the remote space natural warming experiment is mainly realized by means of the natural temperature difference under the change of altitude gradient between Lashihai and Dianchi.Two treatments are set for OTC warming approach: control treatment and warming treatment(EW-II,+3.5±0.5℃);Two treatments are also set for the natural temperature difference of altitude gradient: control treatment(Lashihai)and warming treatment(Dianchi,+3.5±0.5℃).Our results include three aspects.Firstly,in terms of litter decomposition quality residue,different warming approaches accelerated the decomposition of litter of four species,and the decomposition was faster under the natural temperature difference of altitude gradient.Among them,the difference of refractory litter(Zizania caduciflora and Schoenoplectus tabernaemontani)with high carbon and nitrogen ratio was more significant than that of easily decomposed litter(Sparganium stoloniferum and Hippuris vulgaris)under the two warming approaches.In the OTC warming approach,the decomposition rates of litter in the three decomposition stages were also different,in which the submerged stage > Lodging stage > standing dry stage.Secondly,in terms of key compounds,the decomposition rate of litter under the two warming approaches was significantly negatively correlated with the initial carbon related compounds,while the changes of key compounds at the end of litter decomposition were significantly different in different species and different warming approaches.In order to further explain the reasons for the variation of key compounds in litter,the variance analysis of Adonis was used to establish the contribution degree(RCC).Among them,the species under OTC warming approach contribute more to the indicators of key compounds in litter decomposition(RCC < 1),and the warming contributes more to the changes of key compounds in litter under the natural temperature difference of altitude gradient(RCC < 1).The changes of total nitrogen concentration and carbon nitrogen ratio under the two warming approaches have a higher response to warming than that of species(RCC > 3).Therefore,these two indicators can be used as indicators for the decomposition of litter in response to temperature changes during the withering stage of wetland emergent plants.Finally,the influence of environmental factors and habitat on litter decomposition characteristics.The decomposition of litter under the natural temperature difference of altitude gradient is mainly affected by the change of temperature.The contribution of the interaction between precipitation and temperature to litter decomposition is 44.1%,which is higher than that between temperature and environmental factors.Therefore,precipitation is the second driving factor affecting litter decomposition besides temperature.The two driving factors had significant positive effects on the changes of key compounds in litter.Under OTC warming approach,warming increased the influence of habitat on the residual rate of litter mass and the change of key compounds in litter.Therefore,temperature and precipitation are the main driving factors of litter decomposition characteristics under the natural temperature difference of altitude gradient,while the important influence of habitat on litter decomposition characteristics is highlighted under OTC warming.The above results support the view that the natural temperature difference experiment of altitude gradient on large-scale spatial gradient may amplify the response of some ecological processes to climate warming.By comparing the litter decomposition characteristics of dominant wetland species in Northwest Yunnan under two warming approaches for the first time,we explained the warming mechanism,advantages and limitations of different warming approaches and the response of wetland species to different warming approaches,which is of great significance for further evaluating the impact of climate warming on key processes of Wetland ecosystem(such as litter decomposition). |
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