Chinese whispers.

It's not just through the air that plants can send chemical signals to each other. In fact, they are talking to each other right under your feet in an area under the soil known as the rhizosphere. The rhizosphere is derived from the Greek word rhiza - meaning root. This is broadly defined as the area around a plant root that is inhabited by microorganisms, which are influenced by the plant and the chemicals it releases. As different plants and roots cannot be defined as one shape, the rhizosphere refers to the gradient of chemical, physical and biological processes that occur either longitudinally or radially along the root. (Hartmann et.al 2008).

 It is here that scientists have witnessed the secretion of soluble chemicals into the rhizosphere, which are then transported by the mycelium, which are in turn received by neighbouring plants. The mycelium is formed by fungi. It consists of a mass of thread - like hyphae, which acts as a branching network. The mycelium has been referred to as the plant worlds’ version of the internet.

A team in Israel recently demonstrated one particular way in which this method of communication can benefit plants. They found that when placed under stress, unstressed plants are able to respond to stress cues which are emitted from their stressed neighbours. Interestingly, once they receive this cue, they will pass it onto unstressed neighbours which are further away from the original signaler. The experiment was carried out by blocking or allowing root and shoot communication.  After exposing the initial plant to drought - like conditions, it only took 15 minutes to initiate a response – a neighboring plant closed its stomata. The stomata allows for exchange of gases. Plants can reduce water loss by closing the stomata, which are found on the leaf surface. Like a game of dominos, after one hour, all unstressed neighbours had closed their stomata. The plants that were not allowed root contact had left their stomata open. This has indicated that plants are able to anticipate hazard and stress and thus prepare themselves. (Falik et al 2011). This is not the only way that plants have been found to communicate through the ground. Another mechanism, Common Mycelium Networks (CMN’s) will explored next week. Understanding these networks can be of great significance to agriculture. These communication systems could lead to new methods of preparing crops for stresses such as an influx of predation or like in this study, drought.

Falik, O., Mordoch, Y., Quansah, L., Fait, A., Novoplansky, A. 2011. Rumor has it: Relay communication of stress cues in plants. PloSONE 6(11):e23625, doi:10.1371/journal.pone.0023625

Hartmann, A., Rothballer,M., Schmid, M.2008. Lorenz Hiltner, a pioneer in rhizosphere microbial ecology and soil bacteriology research. Plant Soil, 312: 7-14.