Rhizosphere: a communication between plant and soil

• Plant survival and crop productivity are strictly dependent on the capability of plants to adapt to different environments. This adaptation is the result of the interaction among roots and biotic components of soil. The research on plant soil interaction is focused on the processes that take place in the rhizosphere, the soil environment surrounding the root. Many of these processes can control plant growth, microbial infections and nutrient uptake. • Our understanding of the biology, biochemistry and genetic development of roots has considerably improved during the last decade. In contrast, the processes mediated by roots in the rhizosphere such as secretion of root border cells and root exudates are not yet well understood. Nevertheless, the ability to secrete a vast array of compounds into the rhizosphere is one of the most remarkable metabolic features of plant roots, with nearly 5% to 21% of all photosynthetically fixed carbon being transferred to the rhizosphere through root exudates. • On the other hand, it is known that the rhizosphere is a densely populated area in which the roots must compete with different plant species, for space, water, mineral nutrients and with soil-borne microrganisms including bacteria, fungi and insects. Root-root, root-microbe and root-insect communications are likely continuous occurrences in this biological active soil zone. Thus, if plant roots are in communication with different organisms, how do roots effectively carried out this communication process within the rhizosphere? • Many papers suggest that root exudates may act as messengers that communicate and initiated biological physical interactions between roots and soil organisms. As already described, plant survival depends primarily on the ability of the plant to perceive change in the local environment. In other studies it has been found the presence of strong feed backs between plant community structures and soil attributes. In this way plants modify soils, making and maintaining the habitat more favourable for growth and survival in stress conditions. Therefore, exudation of organic substances by roots is not a wasteful C and energy losses for the plants, but an evolutionary developed mechanism by which plants “speak” to micro-organisms or to soil. In the light of this, the mobilisation of bioactive organic/humic substances from the bulk soil or the bulk humus is a result of prominent importance.