Always on the hunt for new information that will help my students and one-on-one clients, I am now looking in to some scientific research supporting the concept of plant indicators and accumulators.
Indicators are plants that are observed to thrive under certain conditions. A single plant species may not be good evidence, but plant communities that prefer the same conditions are. The idea is that you can learn to manage your soil based on what plant communities (weeds) naturally thrive in that soil, changing the conditions in your favor. For instance, if you have abundant weed species that prefer acid conditions (not great unless you want your plants taking up aluminum!) you will know you need to raise the pH.
Dynamic accumulators are plants that "mine" the soil of nutrients. People who have studied Permaculture have long used dynamic accumulators. They then use the plants as compost to feed other plants. One way the plants can mine the soil is by having a deep root system and therefore have access to minerals that have been washed out of reach of shallower roots. Phosphorus is a great example of this. It doesn't move very fast through the soil, but eventually it moves below where most plant roots can reach it. If you plant a phosphorus accumulator and it and has a deep root system, you can replenish the topsoil with the compost of that plant.
So why am I looking into scientific research? Because I like to understand exactly how these things work on the molecular level. Also, I think they are two sides of the same coin. Interested? I'll post again when I find evidence.