Masters of Adaptation
Plants: Masters of Adaptation
By Peggy Rudberg
In the 3 billion years since life first appeared on Earth plants have evolved driven by survival. They have been subjected to fire, floods, glaciers, drought, predators, competition and disease. Ninety-nine percent of all species that have ever lived on Earth have gone extinct. Nevertheless, today, plants make up 80 percent of the Earth’s biomass.
“This pinyon pine tree growing out of limestone rock along the rim of the Grand Canyon is subjected to a harsher environment than its neighbors in nearby forested areas. Here, along the rim, frequent high winds and a scarcity of topsoil and water make survival more challenging. The root system of a small tree like this can be enormous, reaching down into the rock cracks and fissures, making it possible for the tree to harvest the water it needs to survive.” National Park Service photo by Michael Quinn
Photo courtesy Grand Canyon National Park, public domain, via Wikimedia Commons
What are the mechanisms that allow some plants to survive? Ancestral conifers that appeared 300 million years ago survived the Pleistocene Epoch with its cycles of glaciations. They produce antifreeze proteins and cold-responsive genes that aid stress tolerance. Their roots grow into the bedrock below soil levels where water stored in fractures and pores is an important and routine source of moisture for woody plants. Leaves are compact and waxy, and conifers have acquired systems to downregulate photosynthesis when bright sunlight and cold temperatures could lead to freeze damage.
An investigation of late-spring frost damage discovered that oak and beech trees can ramp up photosynthesis in the second set of leaves after a first set has been killed and extend fall leaf life. To prepare for possible reoccurring injury next spring, bud growth in the fall can be elevated 66 percent.
Radiocarbon dating confirms that seeds can remain viable in a frozen state for as long as 32,000 years. The seeds of an arctic flower similar to the modern narrow-leafed campion (Silene stenophylla) were found in Siberian tundra permafrost and when planted, germinated and reproduced.
Through recent improvements in tree-ring and ice-core dating starting in the 1960s, accurate climate and atmospheric history is available going back more than 110,000 years. At the end of the last ice age (roughly 11,700 years ago) gradual warming suddenly reversed for 1,200 years before temperatures rapidly climbed 18 degrees Fahrenheit in a few decades to near-current levels. More weather extremes and rising temperatures are predicted.
Some scientists believe that cacti have been around for over 10 million years. Spurred by arid habitats and drought, leaves became spines to discourage predators, reduce transpiration and capture nighttime moisture. Widespread roots developed that can quickly expand to absorb any accessible water and stems evolved into spongy water storage units that shrink and expand. Prickly pear cacti (Opuntia spp.) can tolerate internal temperatures of over 158 degrees Fahrenheit and mature saguaros (Carnegiea gigantea) can store 5,000 liters of water.
A unique southwestern Africa plant, welwitschia (Welwitschia mirabilis), has individuals that may be over 3,000 years old. They have survived where rainfall averages less than one inch per year. Their unusual genetic history beginning 86 million years ago is being studied to understand their endurance and tolerance to hot arid conditions.
Warming temperatures exacerbate drought and wildfires. In Los Alamos, New Mexico, a study was done to determine why some trees survive dry spells while those nearby die. The roots of the piñon-juniper specimens that survived recent droughts have grown into bedrock to access water.
A previously dormant bud sprouts from a coast redwood that was burned and thought to be dead in the CZU Lightning Complex Fire.
Photo courtesy Erik Sather/ Northern Arizona University
California redwoods at Big Basin State Park have recently exhibited a life-sustaining ability to mobilize reserved energy. After 2020’s incinerating fires, dormant buds that began forming centuries ago sprouted new growth from under charred bark.
Another adaptive strategy for survival is to move. Historically plants migrated to different elevations and latitudes gradually as growing conditions changed. New plants expand into more advantageous environments as older populations fail to regenerate in their previous range. In North America some plants have moved over 10 miles to higher latitudes in the last decade while wheat is being planted 160 miles closer to the poles. To relocate, wild plants require migration corridors, but some vegetation will be blocked by natural and human barriers like farms and cities. Plants acclimated to cities may move more easily but may not find appropriate soil or water or suitable pollinators.
In the Rocky Mountains, upslope movement is hampered by the decrease in land area uphill. In New Mexico we have additional circumstances in our sky islands, isolated mountain ranges surrounded by desert lowlands, making latitudinal movement almost impossible. Each elevation level has a distinct ecosystem harboring often unique flora. Within sky islands plants that move vertically replace the adjacent plant communities that may have nowhere left to go.
And some plants seem to have accomplished longevity by sheer numbers, vast distribution and good fortune. Cycads were a dominant flora over 250 million years ago with fossils found from Greenland to Antarctica. Today most cycads are extinct except for the remaining 10 genera that grow in a wide variety of subtropical and tropical environments from grasslands to swamps. Could it be that in a few protected pockets of Earth cycads took shelter and persisted?
The future is by definition uncertain and plants have evolved amazing responses to stress. But the larger question is "Do plants and the human race have time to adapt to global climate model projections of 'widespread, rapid and intensifying' climate change?”
References:
“Champions of winter survival: cold acclimation and molecular regulation of cold hardiness in evergreen conifers,” New Phytologist (Aug. 31, 2020)
“Ancient redwoods recover from fire by sprouting 1000-year-old buds” by Erik Stokstad, Science
(Dec. 1, 2023)
“New study offers cautious hope about the resilience of redwoods,” Northern Arizona University news release (Nov. 30, 2023)
“Increased autumn productivity permits temperate trees to compensate for spring frost damage,” New Phytologist (Sept. 21, 2018)
“32,000-Year-Old Plant Brought Back to Life – Oldest Yet” by Rachel Kaufman, National Geographic News (Feb. 13, 2012)
“Younger Dryas,” Britannica
“Latest ice core analysis shows sharp warming spike in Greenland” by Seth Borenstin, Associated Press for PBS Newshour (Jan 18, 2023)
“A Plant That ‘Cannot Die’ Reveals Its Genetic Secrets” by Richard Sima, The New York Times (July 31, 2021)
“How do conifers survive droughts? Study points to existing roots, not new growth” by Charlotte Hsu, University of Buffalo Research News (Jan. 2, 2020)
NOTE: This story was featured in the February 2024 SFEMG Newsletter