The Degradation of the Asphalt Alleys by Rhizomes of Herbaceous Plant Species of Couch Grass

摘要

The soil cover of urban areas consists of several soil taxonomic units with significantly altered properties and functions. Soils covered by asphalt or another compact materials (such as concrete materials), also known under the name of or ekranic Technosols [1, 2], have strongly modified properties and perform only part of the specific functions that allow only low biological activity and root growth of some plants species. Soil under asphalted alleys have water retention capacity and allows expansion of the roots of woody plants and grasses. The soil horizons under asphalt pavers can be developed only a small number of plant species that are tolerant of deficient aeration. It is well known that the concentration of oxygen decrease considerable and the concentration of carbon dioxide increase significantly (>10% or even 20%) in the compacted soil layers or in the soil layers under asphalt [3, 4]. Some physical soil properties of such as bulk density, compaction degree, air porosity, total soil porosity are substantially modified. Frequentlly, the values of physical properties of soils covered with asphalt indicate that soils are a strong compacted. Under these circumstances the soil covered with asphalt can be explored by a smaller number of plant species. Case studies conducted in several locations of urban area from Romania showed that soils under asphalted paths or alleys keeps some undisturbed soil properties such as particle size, mineralogical composition. Some plants roots may continue to grow after pavement is placed over an existing roots system. Some plants species such as Tillia tomentosa, Populus nigra, Populus alba that grow in the vicinity of asphalted paths lead unevenness, cracking and perforation of asphalt path. Even if it seems impossible, the asphalt path can be traversed by plant roots or runners that develop from buds on roots or rhizomes of herbaceous plant species. One of herbaceous plant species able to penetrate asphalt is Cynodon dactylon known under the name of Couch grass, Bermuda grass, Quickgrass, Twitch grass [5, 6,]. Investigations conducted by us in the field have shown that Cynodon dactylon (perennial grasses) is able to cross paths asphalted by runners that develop from buds on the rhizome. The runners of this plant which grow in soil horizon located under asphalt are able to penetrate the asphalt pavers during the hot summer. In some cases, the first runners cross the pavement in the parallel direction to the surface, at a distance of a few centimeters, after that reach the surface. The developed cracks on the asphalt allow growth of other plant species such as Taraxacum officinale (dandelion), Polygonum aviculare (birdweed, pigweed and lowgrass), Hordeum murinum (wall barley or false barley), Lepidium ruderale (narrow-leaf pepperwort, roadside pepperweed or peppergrass), Poa pratensis (Kentucky Bluegrass, Smooth Meadow-grass, or Common Meadow-grass), Cardaria draba (whitetop or hoary cress). Among the main conclusions drawn from the studies mentioned: (i) Some species of herbaceous perennials such as Cynodon dactylon are able to perforate asphalt. Resistance to penetration asphalted alleys shrinks considerably in hot summer days. (ii) High power crossed the thick rhizomes of couch grass is frequently underestimated and not taken measures to prevent degradation of asphalted alleys. (iii) We believe that highlighting the progressive stages of degradation of asphalt paths and knowledge of biological characteristics of herbaceous plant species able to perforate asphalt are important in the establishment and implementation of preventive measures.