School Students’ Work May Help Better Climate Models
A bunch of school students with help from researchers at the University of Arizona have published a paper in the American Journal of Botany that may help better climate models. Their work reveals that the shrinking of dried leaves, if unaccounted for, may make climate models less reliable.
These computer models are based on fragments of data of the Earth’s past that we find in fossils. One such fragment is area of fossilised leaves. Typically, species that spring larger leaves indicate warmer climates and a favourable environment. However, the area of fossilised leaves measured today is not an exact representation of the fresh leaves of the time. Leaves shrink as they dry and get fossilised, and they lose more water in warmer climates thereby shrinking more.
In spite of knowing this many studies assume that shrinkage is negligible and use area of fossilised leaves interchangeably with area of fresh leaves. Thus climate models based on those measurements may well be misrepresentative.
While teaching students at a local high school, Ben Blonder, a graduate student at the University of Arizona, realised that he had a pool of eager beavers that could help him work out whether this hypothesis of shrinking leaves and climate models holds up. After designing some simple do-it-yourself experiments, in 2011 over 100 students stepped out of their classrooms to collect leaves from the Arizona Campus Arboretum.
To show that the extent of shrinkage in fossilised dried leaves is far from negligible, the students carried out an experiment. They replicated the fossilisation process that leaves naturally go through by drying some leaves at 60 deg C, and measured the resulting shrinkage.
The students found that leaves from certain species actually shrink at a much higher extent than previously thought. Leaves of the Colorado ragwort, for instance, shrunk by as much as 41% in area when left to dry. Thicker leaves from other species shrunk by as much as 80%. On average, though, they found that leaves typically shrink by a margin of 10-30%, clearly showing that shrinkage in dried leaves can be substantial. This, they knew, meant that measurement of fossilised dried leaf area could not be interchanged with measurement of fresh leaf area.
But the students did not stop there. To find a way to limit or even reverse the shrinkage of fossilised leaves, the students carried out three further sets of experiments. First, to verify if hydrating drying leaves would have any impact on shrinkage, they dried leaves following the same procedures they initially followed but then placed the leaves in a damp environment. Second, to ensure that a plentiful source of water to the plant does not have any effect on leaf shrinkage, they hydrated the leaves first and then dried them. Third, some leaves were just left in mud throughout.
Leaves that were hydrated following a period of drying, they found, did not shrink by much. This exciting result was the solution to averting the shrinkage problem. Indeed, if fossilised dried leaves are rehydrated before measurement, the resulting area would be representative of fresh leaf area. The students also found that leaves that were buried in mud shrunk even less. This was surprising as it indicates that dried leaves shed from trees in damp environments may not shrink very much at all. Hydrating leaves before drying though had a negligible effect on shrinkage confirming that shrinkage does not depend on the plant’s availability of water.
The students have thus not only shown that leaves may shrink more than initially thought but also propose that fossilised leaves can be hydrated before measurement. Not least importantly, the experiments resonated with the students. Of the 105 students who were involved, 40 completed the requirements necessary to qualify as coauthors on the scientific paper. Bringing such DIY-types of science achieves many things, among which is a unique form of engagement with science.
And it can even make leaves look cool.
Reference: Blonder, B. et al., (2012) The leaf-area shrinkage effect can bias paleoclimate and ecology research, American Journal of Botany. DOI: 10.3732/ajb.1200062.
This article was edited by Akshat Rathi.