TheGerman agronomistHiltner first defined the rhizosphere, in 1904, as the ‘effect’
of the roots of legumes on the surrounding soil, in terms of higher microbial activity
because of the organic matter released by the roots.
Until the end of the twentieth century, this ‘effect’ was not considered to be an
ecosystem. It is interesting to make some brief observations about the size, in terms
of energy and extension, of this ecosystem to determine its impact on how the
biosphere functions. First, in extension, the rhizosphere is the largest ecosystem on
earth. Second, the energy flux in this system is enormous. Some authors estimate
that plants release between 20 and 50% of their photosynthates through their roots. Thus, rhizosphere’s impact on how the biosphere functions is fundamental.
A large number of macroscopic organisms and microorganisms such as bacteria,
fungi, protozoa and algae coexist in the rhizosphere. Bacteria are the most abundant
among them. Plants select those bacteria contributing most to their fitness by
releasing organic compounds through exudates, creating a very selective environment
where diversity is low . A complex web of interactions takes place
among them, and this may affect plant growth, directly or indirectly. Since bacteria
are the most abundant microorganisms in the rhizosphere, it is highly probable that
they influence the plant’s physiology to a greater extent, especially considering their
competitiveness in root colonization