UNIVERSITY PARK, Pa. — David Eissenstat, professor of woody plant physiology, retired recently after a distinguished 28-year career on the Penn State College of Agricultural Sciences faculty, including a two-year stint as interim head of the Department of Ecosystem Science and Management.

Eissenstat built a storied research career in root biology, during which he helped Penn State achieve international recognition as one of the best programs in the world in the area of plant ecophysiology, according to Rick Roush, dean of the College of Agricultural Sciences. In addition, he made major contributions to the University.

“Dave provided strong leadership, chairing Penn State’s Intercollege Graduate Degree Program in Ecology from 2007 to 2017, and I especially appreciated his willingness to take the job as interim head of his department for several years when we needed his steady guidance and experience,” Roush said.

Eissenstat left a mark on his field, noted Bradley Cardinale, current head of the Department of Ecosystem Science and Management. “His work looking at how root biology and ecology respond to ecosystem change led to about 180 peer-reviewed papers that have been cited more than 19,000 times,” Cardinale said. “His work led to him being inducted as a fellow by the American Association for the Advancement of Science in 2022, and he was named a fellow of the Ecological Society of America in 2017.”

Eissenstat suggests that his main scientific contributions have advanced the understanding of the roots of woody plants, particularly forest trees and fruit crops. Much of this work was centered on understanding the trade-offs between thin, metabolically inexpensive roots that grow and take up nutrients quickly — but are short-lived — versus longer-lived roots that are thick, well defended, and often more reliant on soil fungi.

“I have had the opportunity to develop collaborations across the University and several countries in Europe and Asia,” Eissenstat said. “But my students have been my greatest source of pride. They have had significant achievements, and many continue to improve our understanding of plants, especially in the area of belowground ecology. I was fortunate to have my research regularly supported by the National Science Foundation, the U.S. Department of Agriculture, and the U.S. Department of Energy.”

A colleague of Eissenstat’s, Jason Kaye, distinguished professor of soil biogeochemistry, calls him one of the most important root biologists of his time.

“Having him in the College of Agricultural Sciences and the Department of Ecosystem Science and Management has been a boon to our international visibility and recognition,” Kaye said. “His research broke new ground in understanding how the size and growth rates of roots vary among woody plants. And he used these careful measurements of roots to understand how whole ecosystems depend on root properties.”

Kaye, who now chairs the ecology graduate program, added that the program thrived under Eissenstat’s leadership. “We have much to thank him for — I relied heavily on Dave’s mentorship and expertise when I became chair,” he said. “And now, years later, I can see that many of the good practices that he put in place continue to support students and faculty.”

In addition to his work at Penn State, Eissenstat also was a visiting professor and senior fellow at the University of Bologna in Italy and with the Chinese Academy of Sciences. He also served as a scientific adviser to the journals New Phytologist and Tree Physiology for the past 27 and 20 years, respectively.

Eissenstat conducted substantial research in the Critical Zone Observatory project at Shale Hills in the Penn State Sustainable Forest, where he collaborated for almost 20 years with Susan Brantley, Evan Pugh University Professor and the Dr. Hubert Barnes and Dr. Mary Barnes Professor in Geosciences. He was an exceptionally perceptive colleague, she pointed out.

“Rather than reciting what I learned from him about how rocks control roots and roots control rocks, I would rather mention what I learned from him about life,” she said. “In navigating academia, it is rare to find real wisdom — it is common to find intelligence, but not wisdom. Dave is wise. In dealing with people problems, he is steady and thoughtful.

“For me, this extended from life to work,” she added. “When I lost my mom to cancer, he counseled me, and when we had issues around sharing resources among the team, he counseled me.”

Investing considerable time training a new generation of scientists at Penn State, Eissenstat advised 28 graduate students and 17 postdoctoral fellows. One of those, Luke McCormack, who received his doctorate in 2012, pointed out that Eissenstat’s ability to help shape and sharpen the skills of early career researchers was not a secret.

“For the relatively brief period that I was at Penn State, I saw that each student or postdoc who worked with him on individual projects learned from his focused mentorship and grew as a scientist and as a person,” McCormack recalled. “As chair of the ecology program and department head, Dave worked to develop supportive, inclusive and rigorous programs where diverse students could thrive.”

Michela Centinari, associate professor of viticulture, co-advised two graduate students with Eissenstat and developed an admiration for his dedication to them. And he helped her greatly as she navigated the tenure process. She considers him a role model and mentor.

“Not only was he always available with useful suggestions, but he also took the time to teach me how to improve my writing, critical-thinking and advising skills,” she said. “Aside from his many career accomplishments, the thing I admire most about Dave is his scientific curiosity and genuine excitement about woody plants ecophysiology.”

Colleague Erica Smithwick, distinguished professor of geography, called Eissenstat a true scholar. She resorted to some soil scientist word play to describe his strengths:

“He would encourage students to dig deeper — literally and figuratively — making sure they truly understood what they were observing or analyzing. Similarly, as a collaborator, I could always be assured that our ideas were going to be rooted in a deep knowledge of the belowground world and reflect new insights in ecosystem science.” 

In retirement, Eissenstat plans to spend more time with family, including his wife, Brenda, children and one grandchild. With their new camp in the Adirondacks, he and Brenda look forward to more opportunities for canoeing, hiking and cross-country skiing in the backcountry. However, he said, they will keep State College as their home base for the years to come.