Botany Class Pursues Plants in a Varied and Changing World

Mojave National Preserve

Students in the Plant Ecophysiology course, taught by Professor of Biology Barry Logan and Laboratory Instructor Jaret Reblin, pose for a photo in the Mojave Desert, which they visited over Thanksgiving break

Plants possess extraordinary and often beautiful means of thriving in diverse environments. To explore plant structure and function in different ecosystems, and to better understand how a changing climate affects plants, students in the Bowdoin class Plant Ecophysiology spent last semester investigating flora around the world.

The class included a six-day optional trip over Thanksgiving break to the deserts of Nevada, Arizona and California. “They’re extraordinary environments, they’re beautiful, and many of our students have never experienced them,” said Barry Logan, professor of biology and associate dean for academic affairs. “The potential for an environment to have a transformative effect on students is high out there. Not only that, but important aspects of the origins of my discipline of ecophysiology can be traced to public universities of the American West and their efforts to support farming in arid environments.”

Logan and lab instructor Jaret Rebin have been teaching a plant physiology class at Bowdoin together for more than 10 years. This year, they decided to redesign the course to emphasize its focus on how environments influence the form and function of plants.

“One of the great things about the class is that students develop an appreciation for plants not as these passive things on the landscape, but as active,” Reblin said. “Plants have to respond to their environment while being rooted in place. That white pine that is experiencing 20-below temperatures in the winter has to also weather temperatures in the 90s in the summer, and it does that in some cool ways.”

Jaret Reblin and Laura Block examining conifer foliage at mid-elevation in Lee Canyon, NV.

Jaret Reblin and Laura Block ’17 examining conifer foliage at mid-elevation in Lee Canyon, Nev.

Over the semester, the class examined how plants survive in ecosystems from the Arctic tundra to Antarctica, from the redwood forests on the Pacific coast to the scorching Sonoran desert. Several scientific experts (including Dr. Greg Goldsmith ’05) skyped in to Bowdoin’s new media commons space to speak with students about Antarctic flora, drought and tree die-off in the American West, and the uptake of fog by trees in Costa Rica’s tropical montane cloud forests. “We built up our physiological knowledge in the early part of the class and then went about applying it in different environmental contexts,” Logan explained.

Students also studied the impacts of global climate change, such as altered atmospheric carbon dioxide levels, temperatures and patterns of rainfall. “There will be winners and losers in a world with higher carbon dioxide and warmer temperatures,” Logan said. “In places where the growing season is colder, we might see increased agricultural productivity, and places where water is limiting and where they’re already experiencing warmer than optimal temperatures, there will be great costs. Everywhere, species’ ranges may shift.”

In addition, the class looked at how scientists in the past few decades have been investigating plant responses to climate change through a combination of experiments and observations. At the moment, research into climate change and its effects on plants is both intensifying and broadening. “I think the work is heading in two different directions. At larger scales, we have satellites and other tools that enable us to look at whole landscapes and their responses to climate,” Logan said. “Another big push is to focus at smaller scales and begin to connect what we understand about the physiology of plant responses to climate change with their genetics, to single genes or small sets of genes.” He added that this information could help launch new breeding programs for crops that could lessen the environmental burdens of agriculture in future conditions.

A student in the class, Trevor Kenkel ’18, said he will use his new knowledge to improve his start-up aquaponics business in Lisbon, Maine, called Springworks Farm (which the Plant Ecophysiology class visited on a field trip). Kenkel grows organic lettuces, basil and bok choy in a greenhouse, using water fertilized by tilapia fish kept in large tanks. “The tight connection between the lab and lectures has significantly improved my ability to understand plant processes and gather empirical data about them,” he said.

The Trip to the Southwest Deserts

Desert Differences
The iconic, columnar Saguaro cactus is common in the more southerly Sonoran Desert but absent from the Mojave and Great Interior Basin. Why? Cacti evolved the ability to absorb carbon dioxide at night, when the costs in terms of water loss are minimized. They then use that stored CO2 to support photosynthesis during the day. This contributes to their exceptional drought tolerance. However, this feature of their physiology leaves them vulnerable to lethal overheating, since they cannot cool during the day via transpiration (which is roughly akin to perspiration in animals). The extreme succulence (“fleshiness”) of saguaro cacti buffers them against dangerous increases in tissue temperature during hot days. However, this same succulence leaves saguaro cacti vulnerable to the lethal effects of freezing during hard frosts. Hence, saguaro cacti are found in the Sonoran, where hard frosts are extremely rare, and seasonal, albeit limited, rainfall is sufficient to recharge their succulence. They are absent from the Mojave and Great Interior Basin, where hard frosts are common in winter. “This is just one of many examples of the exquisite adaptations to the individual characteristics of southwestern deserts that students explored on our trip,” Barry Logan said.

Nine students traveled from Maine to Nevada on Nov. 24 to explore the deserts and see in person the concepts they had been studying. Bowdoin partially underwrote the travel costs.

Over six days, the students explored two of the four deserts of the Southwest — the Mojave and the Sonoran, and walked among plants of the Great Interior Basin at its southern terminus. Because these deserts differ in their patterns and extent of rainfall, as well as in the occurrence of hard winter frosts, they contain profoundly different plant communities that illuminate key structure-function relationships in plants. See the sidebar for an example of this.

The class checked out Joshua trees and yucca plants in the Mojave, juniper, pinyon pine and sagebrush representative of Great Basin flora, and saguaro cacti and “resurrection” moss in the Sonoran. They visited “the playa,” an area in the Mojave valley floor where rainwater collects and evaporates quickly, concentrating salts and fine sediments. Only saltbush can grow in this sandy, arid soil. Then they stopped by a nearby oasis, which is located over a geologic fault that sends water to the earth’s surface, nourishing a verdant two-acre area of cottonwoods, willows and cattails. Later, they checked out how the salt cedar, an introduced, invasive shrub, has ravaged native riverside plant communities. They also visited Biosphere 2, a research facility that was once the site of an extreme experiment testing whether people could survive in a “sealed autonomous living environment,” according to Logan.

Sofi Lopez ’18, a student on the trip, said her favorite experience was exploring the highs and lows of a mountainous desert environment with desert ecologist Stan Smith, of the University of Nevada in Las Vegas. Smith brought the class near the top of Spring Mountain and led them down to the valley floor, teaching the students about the plants found at varying altitudes. “It was amazing to see the difference between the snowy, pine-covered top and the sandy, creosote-covered flat land at the bottom,” Lopez noted.

Lopez said she signed up for the class because she’s always loved being in nature and around plants but that she didn’t know much about them. The course “opened my eyes to all of the intricate ways plants work,” she said, adding that she is now considering a career in plant science. “The class helped us understand more and more about how plants work as we went along, but also helped us understand more and more about how complex and intricate plants are.”

 

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Meredith Outterson inspects dwarf mistletoe, a parasite infecting a conifer in Lee Canyon in Nevada. An excellent example of the ecological phenomenon of "facilitation" whereby mature ("nurse") plants promote the survival of seedlings, sometimes of another species. Bare desert soil is an unusually stressful environment for seedlings, with direct exposure to sunlight, temperatures extreme and herbivores. The canopy of other plants, therefore, is a microenvironment that promotes seedling survival, often resulting in tight clustering of plants. Prof. Stan Smith (UNLV) discussing the formation of hardened caliche soil layer. Meredith Outterson inspecting mosses capable of surviving nearly complete desiccation along the trail in Saguaro National Park outside of Tucson, AZ. A hillside dominated by saguaro cacti and creosote bush in Saguaro National Park outside of Tucson, AZ. A delicious Thanksgiving dinner at Ruperto's in Parker, AZ. Desert ecologist Prof. Stan Smith (UNLV) highlights the manner in which the branching patterns of blackbrush deter herbivores. The seasonally dry river bottom (floodplain) of the Bill Williams River in Arizona (in the Bill Williams National Wildlife Refuge).  The coppery colored plants are saltcedar (different from salt bush). Saltcedar is an introduced, exotic plant that has invaded riparian (i.e., on the edges of rivers) habitats in the Southwest and devastated native vegetation. Control of river flow through the construction of dams has modified the streamside habitat in ways that favor saltcedar over native vegetation. A private "inholding" in the Mojave National Preserve that supports cattle grazing. The effects of grazing on this extreme, delicate plant community are evident. Introduced, invasive salt cedar (the golden shrub shedding its leaves for winter) beneath a dead, native cottonwood along the banks of the Bill Williams River near Parker, AZ. Dams, which prevent seasonal flooding and lower the water table, and salt cedar, which enriches the soil with salts, have created soil environments lethal to native vegetation throughout the southwest. The lush plant community of a desert oasis, located not more than a few hundred meters from the barren playa. Students and Prof. Logan in the Mojave National Preserve. Students in the Mojave National Preserve. Saltbush in the playa. Pinyon-Juniper woodland representative of much of the Great Interior Basin. Wild burros among Joshua trees in the Mojave Desert near Las Vegas, NV. Victor Leos examining the fibrous quality of Joshua tree foliage. Blackbrush dominated Mojave Desert Flora in Southern Nevada Creosote bush dominated low elevational Mojave desert. Prof. Stan Smith discussing Great Basin topography with students of Plant Ecophysiology Ponderosa pine dominated forests near the peak of Spring Mountain.
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