Leaf study brings boom to CZO
UNIVERSITY PARK, Pa -- It wasn't hunting season, but a Penn State researcher took aim at the target and fired. Nothing moved except some leaves floating gently to the ground – a perfect shot.
It was those leaves that Penn State graduate student Lillian Hill and her team were after earlier this year when they trekked out into the woods with a shotgun. It may seem unusual, but it's actually a common method to bring down samples that grow high in the canopy – called sun leaves.
It's those hard-to-reach leaves that Hill needs. She is studying what nutrients trees take from their leaves before dropping them, and what that process can tell us about what's happening underneath.
"Plants suck up whatever is in the soil that they need, and they put it in their leaves to do the types of reactions they need to keep themselves going," Hill said.
Before the leaves fall, plants resorb any nutrients they need to reserve for the next year. If they take back a specific nutrient, it might mean they are not getting enough from the soil.
"That's why we are looking at older canopy trees, they kind of learn what to resorb," Hill said, whose advisors are Jason Kaye, professor of soil biogeochemistry, and Roman DiBiase, assistant professor of geosciences and associate in the Earth and Environmental Systems Institute at Penn State.
Hill will head back out to the woods this month to collect more samples. Her job will be much easier, thanks to the changing seasons. Hill will take the live leaves she previously collected, and the dead leaves she'll find this fall, run them through equipment in the lab, and compare nutrient content.
Her work can tell us what nutrients are missing from the soil and therefor what is limiting trees' growth in any particular location. This can also offer researchers information about the soil and bedrock underneath are interacting.
Hill is comparing limiting nutrients at locations with shale bedrock and sandstone found within Penn State's Susquehanna Shale Hills Critical Zone Observatory.
"We're also taking soil samples out here at multiple depths and analyzing that for the same suite of nutrients," Hill said. "That gives us an idea if there is a difference in nutrient limitation between sandstone and shale. That's my big question."
The sites are part of Penn State's CZO, one in a network funded by the National Science Foundation that links diverse geographical locations across the U.S. where researchers are studying the thin layer that supports all human life. Dr. Susan L. Brantley, Distinguished Professor of Geosciences and Director of the Earth and Environmental Systems Institute at Penn State, is principal investigator of the Shale Hills CZO.
Hill's work represents a small portion of the voluminous, cross-disciplinary research happening at any time in the CZO. Her project, and others, provide new lines of evidence in the study of how rock, soil, water, air and living organisms interact and shape the Earth's surface.
Penn State conducted research on Hill's project with permitting and cooperation from the Pennsylvania Department of Conservation and Natural Resources, which also uses the shotgun method.