GETTING TO THE ROOT OF IT ALL
Root Exudates and Microbial Relationships
Root systems are able to change the environment directly
surrounding them by secreting a wide range of organic
compounds, known as root exudates and mucilage, and
releasing ions that influence pH. As positive ions (cations
Ca2+, K+, Mg2+, etc.) are removed from the nutrient solution,
hydrogen ions (H+) are released from the root system,
equalizing the ratio of anions to cations in the root zone
and thereby lowering the pH of the solution. When crops
begin an active growth phase, anions (NO3, etc.) are taken
up and increase the pH through the release of hydroxyl
ions (OH-) into the solution.
“ROOT SYSTEMS are able to
change the environment directly
surrounding them by secreting a
wide range of organic compounds.”
In the past, root exudates in hydroponics were a cause for
concern. In the early days of soilless culture it was believed
these organic compounds would rapidly build up in the
limited root zone and restrict plant growth. This turned out
not to be the case in most circumstances. Instead, it is now
believed that the vast array of compounds plant roots excrete
can account for between 5 and 21% of the photosynthetically fixed carbon, which is a significant cost to the plant. For
that reason, the plant must obtain some benefit from secreting compounds into its rhizosphere, and this is something
researchers are investigating in some detail. Root