Effects of selected root exudate components on soil bacterial communities
Root exudates are substances that plant roots secrete into the rhizosphere, stimulating microbial activity which in turn helps to support a healthy soil system and productive garden. The exudates are composed of a mixture of compounds each with its own unique properties.
A group of scientists from New Zealand wanted to know which of the exudate-constituents affected microbial growth the most. They did this by selecting six of the most common root exudate components: sugars (a mixture of fructose, glucose, sucrose), lactic acid, maleic acid, and quinic acid. With these ingredients, five artificial exudates were concocted to make treatments: sugars, sugars+all acids, sugars+individual acids). The artificial exudates were then watered into soil over a 14 day period. After the 14 days, microbial activity was measured (microbial activity can be measured in bulk, it gives us a good idea of population size). Also, the numbers of species (or diversity) in each treatment was quantified.
The scientists found that the most effective recipe to promote microbial activity was the combination of sugars and lactic acid. The high level of microbial activity indicates that this treatment had the highest microbial populations. Interestingly, the sugar/lactic acid brew had the lowest diversity. The most diversity was seen in the sugar/maleic acid brew. Even more interestingly...the sugar/maleic acid had the lowest amount of microbial activity. The scientists suppose that the sugar/lactic acid brew enabled the most efficient group of microbes to quickly proliferate, while the sugar/maleic acid caused slower growth which allowed a diversity of bacteria to grow. The combination of sugars and quinic acid, as well as the combination of sugars and all of the acids produced relatively high microbial activity as well as species diversity. Take home message, use a diverse food source for your teas, and you will have a diverse and abundant microbial community. Thanks Kiwis!