| As important global climate change scenarios,the increase of atmospheric nitrogen deposition and the change of precipitation pattern will directly or indirectly lead to the change of ecosystem nitrogen cycle and water cycle,which will change the plant growth.Picea koraiensis Nakai is one of the constructive species of spruce fir forest in the Xiaoxing’an Mountains of our country.And it is one of the major afforestation species in the Northeast China.This tree species occupy an important position in the cold-temperate coniferous forest in China.Therefore,exploring the response of the red-spruce to the severe climate change scenarios in recent years is of great significance to the development dynamics of the spruce fir forest.In this paper,two annual spruce（Picea koraiensis）seedlings were selected as the research object.The seedlings of Picea koraiensis were treated with nitrogen and water.The increase of nitrogen is divided into four levels:high nitrogen HN(15 g N m-2a-1),medium nitrogen MN(10 g N m-2a-1),low nitrogen LN(5 g N m-2a-1)and control CK（no addition）,water-reducing treatments were achieved by artificially reducing the amount of water,divided into two levels:natural precipitation（WW）and minus one third of precipitation（WS）in order to study the effects of growth and physiological characteristics of Picea koraiensis seedlings on nitrogen deposition and precipitation reduction response in order to provide data support and scientific basis for the growth dynamics of the species in the future climate change.The main conclusions are as follows:（1）Appropriate amount of nitroge addition can effectively promote the growth of seedlings of Picea koraiensis,and the drought stress on seedling growth can also be effectively alleviated under proper amount of nitrogen addition.However,when the amount of N sedimentation is too high,N addition will aggravate drought stress on seedling growth.（2）Seedlings adopt different biomass allocation strategies under nitrogen deposition and reduced water conditions.Nitrogen deposition promotes seedlings to allocate more biomass to aboveground parts,especially to leaves.But seedlings allocated more biomass to belowground parts under water reduction treatment.（3）Compared with the N and P contentration of each organ,the C contentration of the organs of Picea koraiensis seedlings was less responsive to the nitrogen addition and water reduction experimental conditions.In addition,the N contentration of all organs of the seedlings responded to the application of nitrogen uniformly,but the response of P concentration to N addition was different between water well and water stress,what’s more,the response of P concentration to treatments varied in different organs,indicating that there was organ difference in the change of P contention.（4）The effects of nitrogen addition and water reduction on the ecological stoichiometric characteristics of Picea koraiensis seedlings are different at different growth stages,and the responses between organs are also different.Therefore,a single sampling during the experiment and only one The results obtained from organs（such as leaves）may not be reliable.（5）The change of seedling C:N under each treatment group was mainly caused by the change of N concentration.The change of seedling N:P under each treatment group was mainly caused by the change of P concentration.（6）In the last few months of simulated nitrogen deposition,water reduction and nitrogen application inhibited the elongation and expansion of the first-order and second-order roots of the seedlings,indicating that 1/3 of the water used in this experiment had an inhibitory effect on the root absorption of the seedlings.Root morphology cannot develop in a direction that is more conducive to water absorption.However,the interaction between N and drought makes the appropriate amount of nitrogen addition can effectively relieve the negative effects of drought stress on the root morphology. |
