Roles of allelopathy in plant biodiversity and sustainable agriculture

Allelopathic compounds are metabolites released from plants that might be b eneficial or detrimental to the growth of receptor plants. These compounds are involved in the environmental complex of managed or natural ecosystems. Allelopathic compounds have been shown to play important roles in the dete rmination of plant diversity, dominance, succession, and climax of natural vegetation and in the plant productivity of agroecosystems. The overuse of synthetic agrochemicals often causes environmental hazards, an imbalance of soil microorganisms, nutrient deficiency, and change of soil physicochemic al properties, resulting in a decrease of crop productivity. The incorporat ion of allelopathic substances into agricultural management may reduce the use of synthetic herbicides, fungicides, and insecticides and lessen enviro nmental deterioration. Scientists in many different habitats around the wor ld have demonstrated the above examples previously. It is known that most v olatile compounds, such as terpenoids, are released from plants in drought areas. In contrast, water-borne phytotoxins, such as phenolics, flavonoids, or alkaloids, are released from plants in humid zone areas. Both allelopat hy and autointoxication play an important mechanism in regulating plant bio diversity and plant productivity. A unique case study of a pasture-forest i ntercropping system, which is particularly emphasized here, could be used a s a model for forest management. After the deforestation of coniferous or h ardwood forests, a pasture grass, kikuyu grass (Pennisetum clandestinum), w as transplanted onto the land. The grass was quickly established within 6 m onths. Significant suppression of weed growth by the kikuyu grass was found ; however, the growth of coniferous or hardwood plants was not suppressed b ut stimulated. This example as well as others described in this text clearl y indicate that allelopathy plays a significant role in sustainable agricul ture. Nevertheless, room for allelopathic research in the next century is a vailable for biologists, biochemists, biotechnologists, and chemists. Futur e allelopathic research should focus on the following tasks: (I) a continuo us survey of potential allelochemicals from natural vegetation or microorga nisms, (2) the establishment of practical ways of using allelochemicals in the field, (3) to understand the made of action of allelopathic chemicals i n receptor organisms, (4) to understand the role of allelopathic chemicals in biodiversity and ecosystem function, (5) to explore advanced biotechnolo gy for allocating allelopathic chemical genes in plants or microorganisms f or biological control, and (6) to challenge the natural product chemists to develop a better methodology for isolating allelopathic compounds or their degraded compounds from the environment, particularly the soil environment .