Study On The Fine Roots Characteristics Of The Ancient Platycladus Orientalis In The Mausoleum Of The Yellow Emperor

The Mausoleum of the Yellow Emperor is an important symbol of the great national spirit of the Chinese nation and the spiritual home of the Chinese all over the world.It has the oldest and largest oriental arborvitae in China,owing more than 80,000 ancient cypresses.The vast ancient cypresses have witnessed the glorious history of the Chinese nation for 5,000 years,which were very precious natural and cultural heritage.Due to the aging of trees,the decline of physiology,the infestation by diseases and pests,and the aggravation of human interference,which leads to the growth environment is damaged and the gradual weakening of tree growth is widespread.Because of the threat of death,it is urgent to protect and rejuvenate the ancient trees.The healthy continuation of ancient cypress is inseparable from the healthy and vigorous roots.Roots can not only anchor plants,but also act as an important medium for plants to obtain resources from the soil.As an important part of tree root system,fine root is the main absorber of soil water and nutrients.The vigorous trees with abundant fine roots can obtain more nutrition,which is beneficial to the healthy growth and development of individuals.Therefore,the research on the characteristics of fine roots is of great significance to the protection and rejuvenation of the ancient trees.In this paper,the characteristics of fine roots with different health conditions,different tree ages and different soil ventilation measures were studied.The main conclusions are as follows:（1）The fine roots from trees of different health conditions were different in vertical distribution,anatomical structure and physiological activity:the root length density,root specific surface area,specific root length and biomass of fine roots of the healthy cypress are greater than the unhealthy and the weak trees.The first two orders of fine roots of the healthy and unhealthy cypress are in the primary growth stage,while only the 1^st order fine roots of the weak cypress are in the primary growth stage.Compared with the unhealthy and the weak cypress,the content of malondialdehyde（MDA）and hydrogen peroxide（H₂O₂）in fine roots of the healthy cypress was the lowest,and the root activity as well as the content of soluble protein was the highest.However,the activity of SOD,peroxidase（POD）and catalase（CAT）were the highest in the fine roots of the unhealthy cypress.（2）The fine roots from different aged trees were different in vertical distribution,anatomical structure and physiological activity:the root length density,root specific surface area and specific root length of the 20a trees were the highest,and the 300a trees were the smallest.But the biomass showed an opposite trend.The first 3 orders in fine roots of the20a cypress were in the primary growth stage,while the first two orders of fine roots in100a and 300a cypress were in the primary growth stage.There was no significant difference in SOD activity among the fine roots of different tree ages.The content of MDA and H₂O₂ in the fine roots of 20a cypress were the lowest,and the root activity as well as the content of and soluble protein were the highest.The POD and CAT activity of the 100a trees were the highest,and the root activity as well as the content of and soluble protein of the 300a trees were the lowest.（3）There are different levels of differences in soil factors of different tree health conditions:soil temperature has no significant influence on the health conditions of trees.There were significant differences in soil water content,compactness,ammonium nitrogen,available phosphorus and available potassium content in the soil of cypress under different tree health conditions.In soil with high water content,sufficient nutrients and low soil compaction,the fine roots grew more vigorously and trees were strong.（4）The vent hole rejuvenation method could promote the growth and the development of fine roots of the ancient cypress.The closer to the vent hole,the greater the length and density of the fine roots.The fine roots of cypress in well-ventilated soil can be divided into3 orders,while those in poorly ventilated soil can only be divided into three orders.The closer to the vent hole,the less the accumulation of MDA and H₂O₂ in the fine roots,the greater the activity of POD,CAT,soluble protein content and root activity.The influence range of vent is within the circle area of 50-75cm radius with its center,and the optimal layout density of vent is 1-2 pieces/m².