The differences among roots

The diversity of leaf types is well known to most children of grade school age. The needles of pines are different than the broad leaves of oaks. Roots on the other hand are a different matter. What two species represent the opposite ends of the spectrum for roots? How should we classify them? Or are most roots the same, its root systems that differ? Or are the basic differences at the cellular level?

In another post, I'll talk about some of what we're learning about differences among species in the anatomy of roots, but for now it's good to think about the things we can see with our naked eye. I'm currently in the middle of an experiment growing over a 100 species of prairie species in containers and looking differences in how the species are built. It's still amazing to wash out roots and see how different two species that can coexist side by side can look like belowground (see picture on left). 

In RSWP, I talk a bit about some of the section pressures on root systems, such as the overproduction of root length when competing for nutrients. Although I've spent a fair amount of time looking at roots, its hard to know who the pines and oaks are of the root world. Roots differ in thickness, hairiness, woodiness, color, connections to mycorrhizal fungi...If pine needles are representative of tough, long-lived, low activity leaves, and oaks wimpy, short-lived, high activity leaves (although there are more extreme versions than oaks, like the lawngrases), the tough-wimpy axis in roots might look something like what is shown above. Yet, it's obvious that the root systems differ between the two. In the early days of ecology, phytogeographers spent a fair amount of time also characterizing root systems of plants, for example tap rooted species vs. species with more lateral roots. We still don't quite understand the full variation of types of roots systems and the selection pressures behind them. In the meantime, I'll keep washing.