Studies On The Causal Factors And Mechanism Of Camphor Tree Yellows

The yellows of camphor-tree is a common and serious disease in Hefei and other cities. The disease can cause the yellows of leaf, decline of plant development, unusual of shape, even the death of the whole plant, and its ornamental value and ecological function were reduced greatly, In this thesis the causes and predisposing mechanism of camphor-tree yellows were studied, and the relationship between the disease and stand condition, soil fertility, physiological and biochemical characteristic were determined in order to find the good methods for control to the disease . The results of investigation indicate: there are many factors for the causes of camphor-tree yellows. The cause of disease varies with the different cities, different streets, even different plants in the same street. However, the key factors that disease occur are that the root is covered tightly with the cement; the soil is polluted by the building garbage or waste or the sewage; soil pH value is too high; the soil texture is too clay and harden which caused by activity of people, and sometimes poor drainage, etc. In the urban environment the coverage of the cement around the root of camphor tree play an important role in the disease. There is obvious positive correlation between degree of the yellows and the earth's surface coverage of cement, namely the more tight the earth's surface is covered, heavier is the degree of yellows. If totally covered by the cement the plant will be very dangerous, even the withered death progressively. In addition, there is no cement cover, the soil texture too harden because of the artificial activity such as park. All these conditions its soil is unfavorable to the growth of camphor tree and the yellows or other diseases will occur. The soil pollution is one of the most important factors affecting the disease. In Hefei city there are three kinds of sources of the soil pollution: (1). pollution from building: which existed already the trees are planted, such as cement, stone, ash, stone lime, brick etc. those were leaved by the project of the roads and building; (2). pollution from engine oil discharged: such as the departments for motor vehicle and all kinds of machines repaired, (3). pollution from the waste water or sewage: of industry: such as waste water of chemical factory and luncheonette, eating-house, laundry, etc. These pollution above-mentioned may cause that the soil was pollution and system of trees roots were poisoned; High soil pH value is a immediate cause of the camphor tee yellows. Soil pH of the area in Hefei is in 5.5-6 under the un-destroy or natural state; while most of the urban camphor trees grow among 8.1 and 9.1 because of suffering pollution of the building or other rubbish. Under the environment of alkaline reaction soil, iron element of soil can not be absorbed by plant normally and make the leaves of plant lacking the iron and yellowsing. The soil texture in urban conditions is too harden and clay, which is one of the reasons to yellows. We hardly see that there existed normal or undestroyed soil which was investigated, Almost every place in city proper the surface of the soil is removed when constrictor and the heart soil that do not suit trees growing were leaved. Soil fertility such as organic content, nitrogen, phosphorus, potassium, copper, iron, magnesium, zinc, manganese etc. have obvious correlation with the disease index. The soil investigated suffered pollution or destruction in various degree, and the content and proportion of nutrition element are unusual state in that it is unfavorable to growth of camphor tree. Within the range where has been investigated, the age of tree is negatively relation with index of yellows disease. In Hefei city, the disease of younger trees is more serious than older trees generally. The growth of tree which suffered disease reduced greatly. For example the length growth of two-year-old branch of disease trees is shorter than that of health trees, and the area of new leaf with disease is obviously diminished too. The photosynthetic...