Response Of Early Spring Plant Growth Strategies In Natural Secondary Forests To Nitrogen Addition

As a special ecological layer in natural secondary forest,early spring plant is an important plant type with research value to cope with global climate change.Increasing atmospheric nitrogen deposition is one of the main driving factors of global climate change,and its ecological effects have become a hot research direction.In order to study the response of early spring plants under natural secondary forest in Changbai Mountain to nitrogen addition,survival strategies and functional characteristics of early spring plants were clarified.In this study,7 species of early spring plants were sampled in Lushuihe Forest of Changbai Mountain,and their net photosynthetic rate,leaf/root morphological characters,above/underground biomass and eco chemical measurements were determined.(1)The net photosynthetic rate of early spring plants increased significantly under the condition of low nitrogen,but decreased significantly under the condition of excessive nitrogen addition.Nitrogen addition increased the nitrogen content in leaves,destroyed the nutrient balance of plants in early spring,and inhibited the net photosynthetic rate.Ranunculaceae is a low N responsive and high N responsive plant,poppy is a N responsive plant and lily is a N responsive plant.(2)N addition had no significant effect on the leaf area,specific leaf area and plant height of plant aboveground morphology in early spring.The plant height of Liliaceae early spring plants and the leaf area of Anemone nigra,Cuscuta japonica and Pseudoplatycarpus chinensis of Ranunculaceae early spring plants increased significantly.(3)For the underground root morphological characters of early spring plants in the experiment,nitrogen treatment increased the total root length and total root surface area,while the average root diameter decreased significantly.The root morphological characteristics of early spring plants of Ranunculaceae and Liliaceae showed an upward trend,while those of Papaver showed an opposite trend.(4)Nitrogen addition can promote the accumulation of aboveground biomass,especially the biomass of leaves and stems.The root to shoot ratio decreased by 16.2% ?27.9% with the increase of nitrogen application,which indicated that more biomass was allocated to the aboveground.Growth strategies of different early spring plants with N addition could distribute nutrients to the aboveground,but the root-shoot ratio decreased significantly,so the biomass distribution pattern changed significantly.(5)N addition increased N content,N: P and C: P in the above/underground parts of early spring plants,decreased C: N significantly,but C,P contents were relatively stable.The N content of the aboveground part was higher than that of the underground part.The growth strategy of early spring plants was more inclined to the uptake of the aboveground part.At the same time,plant N: P increased significantly in early spring,which aggravated the phosphorus limitation.To sum up,nitrogen addition changed the net photosynthetic rate,above/underground morphological traits,biomass and eco-stoichiometry of early spring plants.