Thriving on poison
Many pollutant chemicals, heavy metals, for instance, can be fatal to living systems if their concentrations are high enough. So how is it that what kills one plant will permit another to flourish? Well, there are a number of different mechanisms that have been identified that permit certain plants to exist in circumstances that would kill many others:
1. Rhizoshere biodegredation. This is a synergistic process where the plant releases natural substances into the soil (through its root system) that microorganisms need. In turn, the microorganisms break down the pollutant that would otherwise harm the plant.
2. Phyto-stabilization. Another strategy that plants use is to trap (or imobilse) contaminats within the structure of the plant such that they cannot interfere with vital functions.
3. Phyto-accumulation. A variation on the above; contaminants are taken up with nutrients and water and end up in the plant's shoots and leaves.
4: Phyto-volatilization. Organic contaminants are taken up by plants from soil/water and released to atmosphere through their leaves.
5. Phyto-degradation. Some plants can metabolize and destroy contaminants within plant tissues turning pollution into plant tissue.
6. Hydraulic Control. Trees as natural pumps through their roots which reach the water table. A poplar tree, for example, pulls 30 gallons of water per day out of the water table; and a cottonwood can absorb up to 350 gallons per day. The pollutant can be removed from the ground water by this process.
However, it is also the case that much of our body burden of heavy metals such as cadmium and lead is derived from plants in our diet (or in animal diets) which can bioaccumulate these toxic elements which are naturally present in soils.