| In recent years,due to the combustion of fossil fuels and the rapid development of industry and agriculture,a series of global change problems such as the intensification of nitrogen deposition and the change of rainfall pattern have become increasingly prominent.As one of the important vegetation types in the world,grassland is very sensitive to the changes of water and soil nitrogen availability.As the result of long-term adaptation and evolution of plants to the external environment,plant functional traits have measurable attributes closely related to plant function,and can reflect the environmental change strategies such as photosynthetic carbon acquisition of plants.Bud bank is a set of meristem that can potentially carry out vegetative reproduction.In the grassland ecosystem dominated by perennial clonal plants,is closely related to the renewal and dynamics of vegetation.At present,the research on plant functional traits and bud bank is mostly unilateral,while the research on the relationship between plant functional traits and bud bank construction is still relatively few.Therefore,under the background of global change,it is of great significance to explore the response of key functional traits of Leymus chinensis to nitrogen deposition and rainfall changes and the construction of bud bank for the scientific management of grassland.This paper takes Leymus chinensis,the dominant species in Songnen grassland,as the research object,adopts the two factor full factor design method,and uses the middle universe simulation experiment to set up the experiment of two factors:rainfall（average rainfall 340mm,moderate rainfall 440 mm,and high rainfall 540 mm）and nitrogen deposition(N:0,10 g m-2).The changes of aboveground and underground key functional traits under different rainfall and nitrogen addition treatments and their effects on the construction of bud bank were discussed.It was found that:（1）Under the control condition,the aboveground biomass of Leymus chinensis increased significantly with the increase of rainfall.Among them,the total tiller density of Leymus chinensis increased significantly with the increase of rainfall,and the maximum biomass and density reached 33.53g and 72.25 pieces/plant.The change of rainfall has no significant effect on underground biomass.under the condition of nitrogen deposition,both the aboveground and underground biomass of Leymus chinensis increased significantly with the increase of rainfall.Among them,the total tiller density and the biomass of the mother plant increased significantly with the increase of rainfall.and the maximum biomass and density reached70.18g and 128.88 pieces/plant.（2）Under the condition of no nitrogen deposition,there was no significant difference in the effects of rainfall on plant height,leaf thickness,leaf area,specific leaf area and leaf dry matter content of Leymus chinensis.Under the condition of nitrogen deposition,the plant height,leaf thickness,leaf area and specific leaf area of Leymus chinensis increased significantly with the increase of rainfall.Compared with the control,the indexes increased by21.0%,11.8%,39.1%and 11.4%respectively under the treatment of high rainfall.The dry matter content of leaves decreased significantly with the increase of rainfall,which was10.5%lower than that of the average rainfall treatment.（3）As far as the functional characters of underground organs are concerned,there is no significant difference in the effects of rainfall change on root length,root surface area,root volume,number of root tips and root forks of Leymus chinensis without nitrogen deposition.However,nitrogen deposition significantly increased the root length,root surface area,root volume,number of root tips and root forks of Leymus chinensis under the rainfall condition.Especially compared with the control,the indexes under the highly rainfall treatment increased by 160.8%,105.3%,69.6%and 221.2%respectively.Whether nitrogen deposition or not,the root topological index decreased significantly with the increase of rainfall,which were 0.95 and 0.91 under the control treatment and 0.84 and 0.76 under the high rainfall treatment.The root branching mode changes from herringbone branching mode to dichotomous branching mode.Under the condition of no nitrogen deposition,there was no significant difference in the effect of rainfall on the total number of bud banks,axillary shoot buds,apical rhizome buds and axillary rhizome buds and their daughter shoots,but the coupling effect of nitrogen deposition and rainfall increased significantly,which promoted the number of daughter axillary shoots and daughter axillary rhizome shoots.（4）Leaf area,specific leaf area,root length,root surface area,root volume,root tips and root forks all showed an obvious trade-off relationship with leaf dry matter content.Plant height,leaf area,leaf thickness all showed an obvious trade-off relationship with the topological index.Under different rainfall and nitrogen deposition treatments,Leymus chinensis can maintain its high photosynthetic capacity and provide material source for root growth by increasing leaf area and specific leaf area and reducing leaf dry matter content when ensuring the energy distribution of leaves or when the energy distribution of leaves is fixed;By increasing the root length,root surface area,root volume,root tips and root forks,the root branching mode changes from herringbone branching mode to dichotomous branching mode,expands the contact area between root and soil,quickly occupies a large amount of soil space,improves the efficiency of root transportation resources,and then realizes rapid growth.In terms of the relationship between key functional traits and bud bank construction,the total number of bud banks in Leymus chinensis is mainly significantly affected by plant height,leaf area and root volume.Among them,the number of axillary shoot buds is closely related to aboveground biomass and root surface area,the number of apical rhizome buds is closely related to plant height,leaf area,root volume,root forks and root tips,and the number of axillary rhizome buds is closely related to plant height,leaf area and root volume.In general,under different rainfall and nitrogen deposition treatments,the construction of Leymus chinensis underground bud bank is mainly regulated by two key characters:leaf area and root volume.In conclusion,under the background of global climate change,the changes of rainfall and nitrogen have a significant impact on the biomass production,plant functional traits and bud bank construction of Leymus chinensis.The increase of rainfall and nitrogen deposition significantly promoted the increase of aboveground and underground biomass of Leymus chinensis.Leymus chinensis adapts to the changes of environmental resources by weighing the functional characteristics of leaf and root organs.In addition,under the treatment of increased rainfall and nitrogen deposition,the trade-off relationship of functional traits of Leymus chinensis Leaves and root organs may be closely related to the establishment of bud bank,which may be related to the trade-off strategy adopted by Leymus chinensis in dealing with resource availability.This study is conducive to a deeper understanding of the impact of rainfall change and nitrogen deposition on grassland ecosystem,and provides a theoretical basis for assessing the impact of global climate change on grassland ecosystem. |
