| 单词 | rhizosphere |
| 释义 | rhizosphererhi·zo·sphereR0222400 (rī′zə-sfîr′)rhizosphere(ˈraɪzəʊˌsfɪə)Rhizosphererhizosphere[′rī·zə‚sfir]Rhizospherethe layer of soil (2-3 mm) that surrounds the root of a plant and is inhabited by a large number of microorganisms. The composition of the microflora of the rhizosphere depends on the soil type, ecological conditions, and the age of the plant. The surface of the root is inhabited by microorganisms predominantly of the epiphytic microflora of the seed. The microorganisms, which together are called the rhizoplane, play various roles: they convert certain compounds that are difficult for the plant to assimilate into readily assimilable ones, they synthesize biologically active substances, they enter into symbiosis with the plant, they excrete toxins, and they participate in the process of denitrification. Some representatives of the microflora parasitize plants. rhizosphererhizospherethe particular area immediately surrounding the roots of plants in which their exudations affect the surrounding microbial flora. Many exudations are nutrients which the microorganisms utilize and include carbohydrates, vitamins and amino acids. Conversely, the plant roots may take up minerals released by the microorganisms. Bacteria may be present in the rhizosphere in numbers fifty times greater than in surrounding soil. Gram-negative rods predominate whereas Gram-positive forms are less common than in the surrounding soil. Fungi are usually present in the rhizosphere in similar quantities to those in the surrounding soil, though some plants encourage particular forms. |
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