**3. Allelochemicals as phytochemicals in the plant rhizosphere and its ecological role**

Plant releases a numerous phytochemicals in order to protect it from environmental stresses such as drought, submergence, chemical pollution, UV exposure, pest and disease infection, and several other unfavorable conditions [18, 19]. Through this process, plant produces secondary metabolites and bioactive compounds having potential antioxidative roles [20]. In general, under natural ecosystem, plant releases numerous chemical compounds to the environment from its body and maintains its normal growth and development. However, plant produces several other chemicals/allelochemicals under environmental stress conditions [21–23]. The released allelochemicals create both heterotoxic and autotoxic conditions for the plant and its neighboring species [24]. Under replanting conditions and recycled hydroponics, plant found to produce a number of allelochemicals that inhibit its own growth and development, and this phenomenon has been reported in beans, taro, strawberry, lettuce, several other leafy vegetables, and ornamentals [25–29]. On the other hand, these allelochemicals may play a significant ecological role in controlling weeds, pests, and plant diseases [30, 31].
