INFLUENCE OF ROOT EXUDATES AND RESIDUES ON SOIL MICROECOLOGICAL ENVIRONMENT

Abstract

The effects of grape root exudates and residues on rhizosphere available nutrient, enzyme activity, microorganism quantity and population structure were determined with potted seedlings of Beta (V. vulpine x V. labrusca) as materials. Plant growth was suppressed and available P and K contents in rhizosphere soil decreased, while alkaline hydrolysis N content increased under high concentration of root exudates. As the addition ratio of root residues increased in soil, the contents of available N, P and K in rhizosphere soil increased. The correlation was found between alkaline hydrolysis N content and urease activity under the treatment of root exudates and residues, but the activity of invertase was weakened and had no obvious correlation with soil nutrient or plant growth. Polyphenol oxidase activity was also weakened when the concentration of root exudates and residues increased. The rhizosphere soil was converted from ‘bacteria type’ to ‘fungi type’ under root exudates of high concentration. Under the treatment of root residues, both bacteria/fungi and actinomycetes/fungi ratio increased in rhizosphere soil, however, fungi population diversity reduced. The beneficial trichoderma disappeared, while it appeared with pythium, thielaviopsis and Stilbellales. The results showed that the change of available N, P and K content was not the major reason that led to the depression of plant growth, while the alternation of polyphenol oxidase activity and the change of microorganism quantity and population structure might be the important reason of grape replant disease.