The roles exudate root secretions play in the communication and interaction of plants
is a wide and varied area of study. These exudates can be used as a type of defense
against other plants and in this form act allopathically. They inhibit the
growth, establishment and affect survival rates of neighboring competing plants
and root systems and therefore defend against their resources being taken away (Bais
et al 2006).
The compounds
in which plants use to defend themselves are usually in the form of phytotoxins
but these vary considerably in
composition and function between plants. Exudates need to be at certain
concentration if they are to affect the growth of neighboring plants. Plants
such as Centaurea maculosa and C. diffusa produce their phytotoxins in
high concentrations. These phytotoxins can often work in the favor of invasive
weeds species as in their new environment the native plants may have never
encountered their damaging exudates and therefore no forms of resistances have
evolved. This then gives the weeds an upper hand in taking over these
environments and expanding their distribution. The sensitivity of native plants
to unknown phytotoxins may also explain why invasive species haves such success
in new environments (Bais et al 2006).
Exudates do not
only serve as a purpose in plant defense interactions but also have use for positive
plant to plant interactions. Although these positive interaction are less frequently
documented some root exudates increase herbivore resistance in neighboring
plants which is highly fascinating because it gives a sense of altruism in
plants communities. This is highly debated as it is assumed that in the natural
world organism are generally in competition with each other (Bais et al 2006).
Reference
Bais H. P., Weir T. L., Perry L. G., Gilroy S. and Vivanco J. M. (2006) THE ROLE OF ROOT
EXUDATES IN RHIZOSPHERE INTERACTIONS WITH PLANTS AND OTHER ORGANISMS, Annual review of Plant Biology 57. 233-266p
It’s very interesting to think that phytotoxins could be responsible for species invasions. We know animals can be altruistic, so why do you think that there is controversy over whether or not plants can be altruistic too? Interesting ideas.
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