The Effects Of Root Exudates And Extracts On The Growth Of The Fire-Cured Tobacco And The Activities Of Soil Enzymes

Fire-cured tobacco is one of the important cash crops in tobacco-growing areas of China. Continuous cropping of tobacco brought about many serious problems such as yield decline, quality deterioration and safety reduction. Root exudates and plant remains in soils were concerned as one of the key reasons for these problems in other crops. Therefore, several experiments were carried out to study their effect on the growth of tobacco seedlings and the activities of enzymes in soils. The main objects were to realize the mechanisms and reasons of continues cropping obstacles, to provide scientific information for solving the problems produced by continuous cropping, and to improved the yields and qualities of fire-cured tobacco in tobacco-growing areas of Southwest China.Both pot and simulation experiments together with chemical analysis were adopted in our experiments. The culture solutions with adult tobacco seedlings grown were collected and then fractionated into acid, alkaline and neutral soluble exudates. They were added into culture mediums to investigate the germination rate, the growth and uptake nutrients of fire-cured tobacco seedlings. Moreover, the extracts from tobacco roots were also added into soils to study their effects on the activities of soils.The root exudates soluble in acidic, neutral and alkaline solutions, inhibited the germination of tobacco seeds, indicating some allelopathic substances in root exudates.The growth of tobacco seedlings, especially roots, was inhibited distinctly by root exudates directly obtained from the tobacco culture solutions. The more the concentrated exudates, the more the obvious inhibition to the growth (measured by height), which resulted in low root/shoot ratio and changed little, if any, the length of the largest leaves on the seedlings.All of fractionated root exudates inhibited the growth of tobacco seedlings. The higher concentration of fractioned root exudates added into culture solution, the more reduction of the biomass. In details, the strongest inhabitation to the shoot growth was observed when neutral soluble fractionates were supplied. The shoot biomass with neutral soluble fractionates added was decreased by 10.52% over the blank control, resulting in obvious increase of root: shoot ratio. It suggests that the root exudates would be self-poisonous. Besides, both acid and alkaline soluble fractionates exhibited the trend to increase the stem height and it is necessary to exploit the reasons.The nutrient absorption and activities of the roots were inhibited significantly by root exudates...