Mutant Trees Lay Waste to the Landscape and Reveal Mother Nature's Lean Design

The season of change is upon us here at Minitab's World Headquarters. The air is crisp and clear and the landscape is ablaze in vibrant fall colors. As I drove to work one recent morning, I couldn't help but soak in the beauty surrounding me and think, "Too bad everything they taught me as a kid was a lie."

fall trees You see, as a boy growing up in New Hampshire, I was told that the sublime beauty of autumn was just a happy accident. As the days become shorter, the trees succumb to their own version of seasonal affective disorder; they stop producing chlorophyll because... well, what's the point? As a result of this photosynthetic funk, the green begins to drain from the leaves and the less pragmatic pigments prevail, if briefly.

But thanks to mutant trees, I now know the truth. Or at least one possible explanation. I refer, of course, to the findings of Hoch, Singsaas, and McCown, in their 2003 paper, "Resorption Protection. Anthocyanins Facilitate Nutrient Recovery in Autumn by Shielding Leaves from Potentially Damaging Light Levels."

In truth, I shouldn't say that what I learned as kid was a lie. The theory of autumn by chromatic attrition might still be true to some extent. But I was intrigued to discover recently that newer theories posit a more adaptive role for the annual display. For example, one theory suggests that the bright displays evolved to inform potentially injurious insects that they are barking up the wrong tree. (For more information, see Archetti and Brown 2004, "The coevolution theory of autumn colours".)

But most interesting to me was the discovery that red pigments aren't just late-season hold-outs—production of these pigments is actually ramped up in the fall. Obviously, the "Accidental Autumn" explanation doesn't hold in this case. In their paper, Hoch and colleagues present evidence that anthocyanins, which produce red fall colors, actually help trees prepare for winter.

Here's where the mutants come in. The theory is that the anthocyanins act as a kind of sunblock to protect the leaves while the tree recovers valuable nutrients from the leaves before sending them downward and duffward.

To test this theory, the scientists sampled leaves from normal (wild) trees and from mutant trees that possessed superhuman powers. Well, actually, all trees possess superhuman powers because all trees can produce food from sunlight. (I've yet to meet a human who can do that.) But in this case, affected trees had a mutation that prevented them from producing anthocyanins and turning red in the fall.

It's always easier to understand what your data are showing you when you can look at the results of your analysis in a graph. I used Minitab Statistical Software to create a couple of graphs that illustrate some of the results shared in the paper.

Before and after nitrogen levels

The scientists measured the nitrogen levels in the leaves before and after the period when the trees normally recover as much of that valuable nutrient as they can. This graph shows the before and after nitrogen levels for mutant and wild-type specimens of 3 different tree species. The graph shows that the nitrogen levels in the leaves tend to drop more for the wild trees, indicating that they are more successful at recovering the nitrogen than the mutant trees.

Line plot of before and after nitrogen levels

Resorption efficiency

This bar chart shows the same data, but expressed as "Resorption Efficiency," which is just the percent change between the before and after nitrogen levels. The graph suggests that the lack of anthocyanins hampered the ability of the mutant trees to recover the nitrogen from their leaves.

Bar chart of resorption efficiency

So, rather than simply accepting seasonal spikes in scrap waste, it appears that mother nature is a much better quality engineer than we had given her credit for. In addition to dazzling us with some beautiful color before winter sets in, those brilliant reds are actually adding value to the process by helping to reduce waste.

My newfound appreciation for nature's lean genius inspired me to do a little exploring around Minitab's World Headquarters and capture some images of industrious anthocyanins hard at work improving plant profitability. Along with some cows. If you've never had the opportunity to see trees do this—and even if you have—perhaps you'll enjoy the images shared below.

Happy Autumn!

Corn rows weave under undulating clouds
Harvest has come