Effects Of Nitrogen Deposition On Seed Dispersal And Seedling Regeneration Of Quecus Mongolica And Pinus Koraiensis

Nitrogen addition plots were established at the Qingyuan Forest Ecological Experimental Station of Chinese Academy of Sciences,to investigate the effects of nitrogen deposition on forest regeneration.We performed physical measurements,nutrient analysis,seed release experiment in the enclosures and field,and indoor germination of Quecus mongolica and Pinus koraiensis seeds treated by different levels of nitrogen deposition,to test our hypotheses.The main results are as follows:1.Simulated nitrogen deposition showed significant effects on the physical and chemical traits of P.koraiensis seeds.Simulated nitrogen deposition significantly enhanced the dry weight of seeds,the proportion of seed kernel and the thickness of seed coat.Low level of nitrogen addition significantly increased the concentrations of crude protein and crude fat.However,high level of nitrogen addition showed an opposite effect.2.Simulated nitrogen deposition also affected the physical and chemical traits of Q.mongolica acorns.Low level of nitrogen addition significantly enhanced the fresh and dry weight of acorns,the ratio of acorn kernel and the concentrations of polyphenol(tannins).But crude protein,crude fat,crude starch of acorns were significantly reduced.Medium level of nitrogen addition significantly reduced the physical traits of acorns,but increased the nutriment and polyphenol(tannins)of acorns.3.We investigated the effects of nitrogen addition on seeds selection by rodents in the enclosures.Our results indicated that rodents preferred to cache and eat P.koraiensis seeds without nitrogen addition.However,there was no obvious preference selection to the Q.mongolica seeds treated with different levels of nitrogen addition.4.In the field,different levels of nitrogen deposition failed to influence seed dispersal speed.Low level nitrogen addition significantly reduced the proportion of seeds eaten in situ in P.koraiensis,but increased the proportion of scatterhoarded seeds.Medium and high levels of nitrogen addition significantly increased the proportion of seeds eaten after removal.How level nitrogen addition appeared to increase seed dispersal distances of P.koraiensis and Q.mongolica.5.The germination rate of P.koraiensis seeds increased significantly under low level nitrogen addition,while remained unchanged under medium and high levels of nitrogen addition.Low and medium levels of nitrogen addition significantly increased acorn germination rate of Q.mongolica acorns.Moreover,medium level of nitrogen addition significantly increased seedling height and leaf number of Q.mongolica seedlings.6.Therefore,simulated nitrogen deposition can change the physical and chemical characteristics of the seeds,which can affect the seed dispersal,germination and seedling establishment,and even the natural regeneration process of the forest.