Effects Of Nitrogen,Phosphorus And Potassium Fertilization On The Growth And Physiological Characteristics Of Saraca Dives Seedlings

Saraca dives Pierre,a deciduous tree of Leguminosae and Araca,also known as pyrotechnic tree,is a common ornamental tree species for landscaping in southern China.In forestry production,it can also be used as host of lac insect to produce gum.But at present,the research mainly focuses on the cultivation technology,plant resource application investigation and so on.In this study,according to the results of pre experiment,three factors and three levels L₉（3⁴）orthogonal test design was used in this study.Urea（CO（NH₂）₂）,calcium superphosphate（Ca（H₂PO₄）₂·H₂O）and potassium chloride（KCl）were used as nitrogen,phosphorus and potassium fertilizer respectively.After the experiment,the comprehensive quality of seedlings was evaluated according to their growth and physiological indexes.The experimental results show that:（1）Except for a few fertilization treatments（such as T8 and T9,etc.）,most of the remaining fertilization treatment groups promoted the growth of Saraca dives seedlings.Among them,under T4（N2P1K2—urea 2g/plant+superphosphate 0.8g/plant+potassium chloride 2g/plant）treatment group,the plant height increment,root biomass,stem biomass,leaf biomass and total biomass of Saraca dives seedlings were the maximum;under T5（N2P2K3）fertilization treatment,the ground diameter,leaf length,leaf width,leaf area and leaf perimeter were the maximum;in addition,T7（N3P1K3—urea 3g/plant+superphosphate）treatment had the maximum values.The ratio of height to diameter of seedlings was the lowest under the treatment of calcium superphosphate 0.8g/plant+KCl 3g/plant),while that of T6（N2P3K1 urea 2g/plant+superphosphate 2.4g/plant+potassium chloride 1g/plant）was the lowest.In all growth indexes,N element played a leading role.The results of correlation analysis showed that most of the growth indexes had significant or extremely significant positive correlation with other indexes except stem root ratio.（2）Under different N,P,K ratio fertilization treatments,the Photosynthetic Physiological Indexes of P.glauca seedlings also changed significantly.The results showed that G_S（stomatal conductance）and Tr（transpiration）reached the maximum under T1 fertilization treatment,Pn（net photosynthetic rate）and Ci（intercellular CO₂concentration）reached maximum under T5 fertilization treatment,but Pn（net photosynthetic rate）and Ci（intercellular CO₂concentration）reached maximum under T8 treatment.The results showed that Gs（stomatal conductance）and Tr（transpiration）were the minimum values;In this experiment,all fertilization treatments could increase the contents of photosynthetic pigments（chlorophyll a,chlorophyll b,total chlorophyll and carotenoids）of Saraca dives plants.Among them,the contents of chlorophyll b and carotenoids were the highest under T8 fertilization treatment,and the contents of chlorophyll a and carotenoids were the highest under T7 fertilization treatment.The content of total chlorophyll was the highest.N element played a leading role in all photosynthetic physiological indexes and photosynthetic pigment content.The results of correlation analysis of various physiological indexes showed that except for the positive correlation between photosynthetic pigment content,the positive correlation or negative correlation of other physiological indexes was not significant.（3）The ratio of N,P and K fertilizer also had a significant effect on the seedling and antioxidant enzyme activity.The results showed that all fertilization treatments could increase the content of soluble sugar and soluble protein,and decrease the content of free proline.Among them,T5 treatment had the largest content of soluble sugar and soluble protein,the lowest content of free proline,and T8 treatment had the highest content of free proline.At the level of antioxidant enzyme activity and MDA（malondialdehyde）content,the results showed that all fertilization treatments could reduce the antioxidant enzyme activity and MDA（malondialdehyde）content.Among them,under T9 fertilization treatment,the activities of SOD and pod were the highest,the activities of SOD and pod were the lowest under T5,T3and T7.The content of MDA（malondialdehyde）was the highest in Saraca dives seedlings,and the lowest in T4 treatment.In addition,K element plays a leading role in soluble sugar,soluble protein content,SOD enzyme activity and MDA content,while N element plays a leading role in free proline content and POD enzyme activity.It can be concluded that NPK fertilization can effectively improve the status of plants under environmental stress and improve the resistance of plants.（4）The results of principal component analysis and total analysis of growth and physiological indexes showed that the comprehensive score of plant principal component under T5 treatment was the highest,and that of T8 treatment was the lowest;in the physiological index level,the comprehensive score of plant principal component under T5treatment was the lowest,and that of T8 treatment was the highest;comprehensive principal component comprehensive score of all indexes was conducted The results of component analysis and calculation showed that T5 treatment had the highest score of plant growth and physiology,and T8 treatment had the lowest score.The results showed that under T4treatment,the Qi index of seedlings was the highest,and that of T8 was the lowest.（5）To sum up,T4（N2P1K2—urea 2g/plant+superphosphate 0.8g/plant+potassium chloride 2g/plant）treatment can promote plant height and material accumulation;T5（N2P2K3—urea 2g/plant+superphosphate 1.6g/plant+potassium chloride 3g/plant）fertilization treatment is conducive to seedling thickening and leaf growth;T7（N3P1K3—urea 3g/plant+superphosphate 0.8g/plant+potassium chloride 3g/plant）and T6（N2P3K1—urea 2g/plant+superphosphate 3g/plant）.The results showed that T5（N2P2K3—urea2g/plant+superphosphate 1.6g/plant+potassium chloride 3g/plant）fertilization treatment had the best growth status,while T8（N3P2K1—urea 3g/plant+calcium superphosphate 1.6g/plant+potassium chloride 1g/plant）fertilization treatment could make the seedling growth more robust.Therefore,although the use of nitrogen fertilizer can promote the increase of photosynthetic pigment content and play a leading role in the changes of most indexes,excessive use of nitrogen fertilizer is not conducive to the growth of the plant.