Effects Of Nitrogen Addition On Early Spring Plant Growth Strategies In A Broad-leaved Korean Pine Forest

Under the background of global climate change,the release of nitrogen will cause changes in soil nutrient return,plant growth and development,and biodiversity.This leads to changes in the structure and function of the ecosystem.Early spring plants are a group of herbs that live in the early spring and have a short life cycle.They can tolerate some unfavorable environmental factors such as low temperature and light change by adopting some countermeasures.Even so,early spring plants are very sensitive to changes in the environment.In order to explore the effect of nitrogen addition on plant growth in early spring under the background of global climate change,the experiment of simulated artificial nitrogen deposition was carried out in Pinus koraiensis forest in Xiaoxingan Mountains.Four treatments were designed,namely,control treatment(CK,0g/(m~2.a)),low nitrogen treatment(LN,2.5g/(m~2.a)),medium nitrogen treatment(MN,5g/(m~2.a))and high nitrogen treatment(HN,7.5g/(m~2.a)).The biomass,root morphology,ecological chemical measurement and photosynthetic rate of four early spring plants were measured,and the following main results were obtained:(1)A certain degree of nitrogen addition significantly increased the total biomass and the biomass of each organ of most early spring plants.However,excessive nitrogen addition will reduce its total biomass and the biomass of individual organs.At the same time,the aboveground biomass of early spring plants is more sensitive to the increase of nitrogen than the underground biomass.As far as biomass allocation is concerned,the biomass of early spring plants is closely related to their nutrient absorption capacity and morphological characteristics.(2)With the increase of nitrogen concentration,the specific root length and specific surface area of plant in early spring were significantly different from the average root diameter at the same time.The specific root length and root specific surface area of early spring plants increased with the addition of nitrogen.Compared with the control treatment,the variation of root mean diameter of early spring plants was stable under different nitrogen addition treatments.(3)With the increase of nitrogen concentration,the C content of early spring plants showed a decreasing trend as a whole.However,the N content and P content showed an overall trend of increasing first and then decreasing.According to the element contents of all organs in early spring plants,the element contents of all organs in interspecific species were similar.For the stoichiometric ratio of early spring plants,the C:N of early spring plants decreased with different nitrogen levels,but the N:P of early spring plants increased as a whole.But in the C:P of early spring plants,the difference among species was significant,which was mainly related to the change of P content among species.(4)With the increase of nitrogen concentration,the net photosynthetic rate of early spring plants showed a trend of first increasing and then decreasing.The increase of nutrient elements in the leaves of early spring plants was beneficial to the increase of net photosynthetic rate of early spring plants to enhance photosynthesis.To sum up,the early spring plants in the appropriate level of nitrogen can better growth and development,adaptability to the environment is also more strong.In this study,the biomass,root traits,biostoichiometry and photosynthetic rate of 4 common early spring plants under different nitrogen levels were analyzed in order to further study the adaptation strategies and laws of early spring plants under the background of global climate change,and to provide reference for the study of carbon pools in ecosystems and the conservation and development of local plant diversity.