Effects Of Nitrogen And Phosphorus Addition On The Growth Of Quercus Mongolica Seedlings

In recent years,due to the continuous development of industry and human activities,lead the nutrients of atmospheric dry and wet precipitation increased.In the northeast China,the precipitation rate of nitrogen is 5.78g/m²·a,and phosphorus element is between 0.0093g/m²·a?0.014g/m²·a.Studies have shown that appropriate nitrogen and phosphorus deposition will promote the growth of plants,but too much will cause the imbalance of plant nutrition and reduce the diversity of plants in urban ecosystems.This study used Mongolian oak seedlings as the experimental materials,and simulated the precipitation rate of nitrogen and phosphorus of atmospheric by adding nitrogen and phosphorus fertilizers for three consecutive years,to analyze the influence of seedlings growth,photosynthetic physiology and nutrients content of Mongolian oak under different concentrations of nitrogen and phosphorus fertilizers.And comprehensive evaluation the influence of nitrogen and phosphorus addition on the growth of Quercus mongolica,thereby provide a theoretical basis for the cultivation and application of large seedlings of Quercus mongolica in future urban gardens.The main results are as follows:?1?Nitrogen and phosphorus addition had a significant impact on plant height and ground diameter growth of Mongolian oak.Through three years'continuous addition nitrogen and phosphorus,the highest seedling height growth?151.3 cm?was treated with N1P3,which increased 38.3%compared with CK,and the largest ground diameter growth?32.66 mm?was treated with N1P3,which increased 36.9%compared with CK.In the first year,the treatments with the largest growth of seedling height and ground diameter were N2P3 and N1P3,increased 62.6%and 58.9%respectively;in the second year were N1P3 and N1P1,compared with the group of CK increased 37.1%and 40.1%respectively;in the third year were N3P2 and N2P1,compared with the group of CK increased 38.5%and 41.0%respectively.The addition of nitrogen and phosphorus significantly increased the filling degree of the top buds.Among them,the volume of the top buds was the largest in the treatment of low nitrogen concentration,which was 1.33,1.29,and 1.32 times that under CK treatment,respectively.The area and dry weight of leaves which treated by medium and low concentrations of nitrogen and phosphorus were also higher than those treated with CK.The maximum specific leaf weight was treated by N1P1,which increased 7.0%than CK group.With the increase of nitrogen concentration,the proportion of the aboveground dry weight of Mongolian oak seedlings in the whole plant gradually decreased,the part of underground gradually increased,and the ratio of aboveground dry weight to underground dry weight gradually decreased.?2?Nitrogen and phosphorus addition increased nutrient accumulation in leaves and stems of Quercus mongolica seedlings.In September of the first year,the maximum contents of total nitrogen,total phosphorus and total potassium in leaves were treated by N1P1,N1P1 and N3P1,respectively,which increased 6.4%,10.2%and 5.1%compared with CK.The nitrogen accumulation of leaves was positively correlated with seedling height diameter growth,while the phosphorus and potassium accumulation were negatively correlated.In the middle of July of the second year,the highest treatments of total nitrogen,total phosphorus and total potassium in leaves were N1P3,N1P1 and N3P2,respectively,which increased 28.0%,11.0%and 14.3%than CK.The nitrogen,phosphorus and potassium accumulation of leaves were positively correlated with seedling height diameter growth,among the total potassium content was significantly positively correlated with the growth of seedling height.In September of the second year,the highest contents of total nitrogen,total phosphorus and total potassium in leaves were N1P3,N1P3 and N1P1,respectively,which increased 15.1%,2.0%and 21.0%compared with CK.The nitrogen,phosphorus and potassium accumulation of leaves also were positively correlated with the diameter growth of seedling height.In July of the third year,the highest contents of total nitrogen,total phosphorus,total potassium in leaves were N2P3,N3P2,N3P2respectively,which increased 21.2%,16.7%,20.4%than CK.The total nitrogen content showed negative correlation with the diameter growth,and positive correlation with the seedling height,total phosphorus.And the total phosphorus and total potassium showed positive correlation with the seedling height and,which has a significant positive correlation with seedling height growth.The highest treatments of total nitrogen,total phosphorus and total potassium in the stem were N3P1,N3P2 and N1P3,which increased 9.3%,13.8%and 11.3%,respectively,compared with CK.Besides,the total nitrogen content in the stem was negatively correlated with the seedling height,and positively correlated with the ground diameter growth.?3?The nitrogen and phosphorus addition increased the maximum net photosynthetic rate of Oak seedling,showed the highest N3P2 fitting value,which was 19.50?mol·m^-2·s^-1,and improved the utilization rate of light.Nutrient addition also promoted the dark respiration rate,apparent quantum efficiency,light saturation point and light compensation point of seedlings.The maximum dark respiration rate treatment was N2P3,which increased 2.17?mol·m^-2·s^-1compared with CK treatment;the maximum quantum efficiency treatment was N1P2,which increased0.058 compared with CK treatment;the maximum treatment of light saturation point and light compensation point were N1P3,which increases 373.70?mol·m^-2·s^-1and40.03?mol·m^-2·s^-1compared with CK,respectively.It can be seen from the diurnal variation of photosynthesis that the net photosynthetic rate,intercellular carbon dioxide concentration,transpiration rate,and stomatal conductance were also significantly improved compared with CK treatment,and there was a higher correlation between them.The indicators of diurnal variation of photosynthesis in N1P3 treatment were higher that other treatments.?4?Through principal component analysis,it was found that the growth,physiology and photosynthetic indicators of the Mongolian oak seedling can be divided into three main components.In the first component,the seedling height,ground diameter,nutrient content in stems and net photosynthetic rate were the main dominant factors.In the second component,the ground biomass,leaf transpiration rate and total phosphorus content were the main dominant factors,and the specific leaf weight,bud plumpness,leaf total nitrogen and total potassium were the main dominant factors in the third component.From the cluster analysis of the dendrogram and each treatment growth index data can see the N1P1 and N1P3 bound for a category,with the best growth physiological index and the best seedling quality;the CK treatment has the lowest indicators and the relatively worst quality.Under the comprehensive evaluation of QI seedling quality index,N1P3 had the highest score in each nitrogen and phosphorus treatment,and the seedling quality was the best.