New Method Gives Insight into Plant Characteristics During Global Warm-Up, Says Professor

Royer and colleagues have generated a reliable method to ascertain from fossils from the Eocene period, 34 million to 56 million years ago, the leaf mass per unit of leaf area, an important trait that is related to “leaf economics.” His findings were highlighted at the annual meeting of the Geological Society of America (GSA), which was held in Philadelphia from October 22-25.

“The early Eocene was a period when the planet experienced intense warming,” Royer says. “Quantify the leaf economics of that time allows us to see how plants and the environment around them responded to a warm-up and compare that with what’s happening now.”

Which brings us back to leaf economics, or more precisely, what kind of leaves the plants had and how quickly they grew. In essence, plants tend to be relatively quick or slow growing. Quick-growing plants tend to have a low leaf mass per area. They are typified by thinner leaves, a higher photosynthetic rate and use more nutrients. They also tend to have faster lifecycles and be more susceptible to insect damage. Plants with a high leaf mass per area tend to be slow-growing and have thicker leaves that are more resistant to insect damage. They also display slower photosynthetic rates, use fewer nutrients and longer lifecycles.

Obtaining these types of measurements is simple enough in present day, but, in all but a few examples, has been difficult to generate in the fossil record.

Royer and his co-investigators were able to solve this puzzle by relating leaf mass to the width of the petiole, the thin stalk that connects the leaf to the branch. Heavier leaves require thicker petioles for reasons of support. In fossils, petiole width and leaf area can therefore be measured to estimate leaf mass per area. They tested their methods on Eocene fossils from sites in Washington and Utah.

Royer hopes that this new method will open up a new area of inquiry into the fossil record that can provide important data for helping us understand the effects of climate change today.