From the American Journal of Botany
How a certain species will potentially handle global warming
In the scorching summer heat of the Chihuahuan Desert in southwest Texas, air temperatures can hover around 97°F (36°C) while at the surface of the soil temperatures can exceed 158°F (70°C). Encountering these extreme temperatures, plants must utilize creative methods to not only survive but thrive under these difficult and potentially lethal conditions.
This new work by Dr. Gretchen North and colleagues, published in the December issue of American Journal of Botany (http://www.amjbot.org/cgi/reprint/ajb.1000286v1), sheds light on how one desert resident, the cactus Ariocarpus fissuratus, copes with the effects of high temperatures.
“One crucial point is that small desert plants such as the ‘living rock’ cactus occupy one of the hottest habitats on earth, the surface of desert soils” stated North.
Ariocarpus fissuratus earned its nickname “living rock” because it blends into the rocky surroundings with its small stature that is level with the soil’s surface. The researchers hypothesized that the cactus could “escape” high temperatures by moving more of itself below the soil surface where it is cooler.
Measuring changes in plant depth and root anatomy, North and co-workers determined that the cactus moves deeper into the soil by contracting its roots. But does root contraction play a protective role by modulating temperatures?
To find out, the researchers mimicked summer desert conditions by growing plants on a rooftop in Los Angeles, where air temperature was above 99°F for several days. All the cacti were grown in sandy soil, but half had rocks covering the surface of the soil, similar to their native habitats. For plants grown in rocky soils, the internal temperature of the stem was about 39°F lower than those grown in sandy soils alone. While this may seem like a small decrease, it had a significant effect on the health of the plants.
Unlike the cacti grown in sandy soil which all died, those grown in rocky soil survived the intense heat. Root contraction aided in lowering the internal stem temperature, but only when combined with the cooling effects of the rocky surface. The opposite was true in sandy soil where cacti planted higher above the surface had slightly lower stem temperatures than those planted close to the surface.
“Even in rocky soil, experimental plants attained nearly lethal temperatures during a summer heat wave in Los Angeles” said North. “Thus, root contraction and rocky microhabitats may not provide enough protection should desert temperatures get much higher due to global warming.
CITATION: Tadao Y. Garrett, Cam-Van Huynh, and Gretchen B. North (2010). Root contraction helps protect the “living rock” cactus Ariocarpus fissuratus from lethal high temperatures when growing in rocky soil. American Journal of Botany 97(12): 1951-1960. DOI: 10.3732/ajb.1000286
The full article in the link mentioned is available for no charge for 30 days following the date of this summary at http://www.amjbot.org/cgi/reprint/ajb.1000286v1. After this date, reporters may contact Richard Hund at ajb@botany.org for a copy of the article.
The Botanical Society of America (www.botany.org) is a non-profit membership society with a mission to promote botany, the field of basic science dealing with the study and inquiry into the form, function, development, diversity, reproduction, evolution, and uses of plants and their interactions within the biosphere. It has published the American Journal of Botany (www.amjbot.org) for nearly 100 years. In 2009, the Special Libraries Association named the American Journal of Botany one of the Top 10 Most Influential Journals of the Century in the field of Biology and Medicine.
For further information, please contact the AJB staff at ajb@botany.org.
Caption: A “living rock” cactus (Ariocarpus fissuratus) in a large container on the roof of the biology building of Occidental College, Los Angeles, in June 2008 after 8 days of high temperatures. This particular plants was embedded in sandy soil with surface rocks. Scale bar = 10 mm.
Credit: Gretchen B. North, Occidental College, Los Angeles
5 years ago my neighbour fell for the drought/heat message here in the south of England. He replaced his lawn and rose bushes etc with tough desert type plants in a gravel bed. Needless to say they have been decimated by the wet and the cold.
Neighbors have an ancient patch of Prickly Pear Cacti- imported to NE Oregon from:
Grand Junction Colorado or Climate is similar, and it’s been there for oh, since the last PDO shift. hmm.
Does this “work” have any scientific relevance?
It seems that the desert Flora are smarter than the average Climatologist.
So when the deserts are covered with solar farms what happens to the ecology? Oh stupid me, deserts are barren, nothing there.
CodeTech says:
November 26, 2010 at 8:47 am
Way to anthropomorphize a plant!
No, plants don’t use “creative” methods to do anything. At some point during the evolution of the plant the ones that had deeper roots survived to reproduce and the ones that did not, did not.
But I suppose it’s more “creative” to express this concept as though plants are actively trying to hide from increasing heat. Sigh.
I guess you missed the bit about “Contractile roots pulled plants of A. fissuratus into the soil at rates of 6 – 30 mm^yr”?
I think the researchers were eating the cacti ( Ariocarpus fissuratus is mildly psychoactive).
All of the members of this genus are very very slow growers, do not transplant all that well and have limited ranges. Growing the plants in containers on a rooftop in Los Angeles has no correlation to plants growing in real soil in their native habitat (which really is a micro habitat, i.e. they wont grow everywhere, but only in select locations within their range).
Douglas DC says:
November 26, 2010 at 9:06 am
Neighbors have an ancient patch of Prickly Pear Cacti- imported to NE Oregon from:
Grand Junction Colorado or Climate is similar, and it’s been there for oh, since the last PDO shift. hmm.
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Opuntia species are generally very adaptable, unlike most others. Many, would do just fine in NE Oregon, including O. polyacantha(sp.?) which is common in the Colorado Plateau. N.B. vegetative propagation is not the same as reproduction. One thing Opuntias do very well is vegetative propagation! I have seen massive stands of 100 year old plants in ridiculously unlikely locations.
From a plant physiologist:
The measurement of plant water use was flawed in that the individual containers holding the plants were measured en masse. This means that the claim of no difference in water relations between rocky top soils and sand top only soils is suspect. The rocky soils, with greater albedo and less surface pore space for diffusion of temperature gradient, likely evaporated less, leaving more water to be retained/transpired. These improved water relationships is more realistically associated with reduced stem temperature and increased survival. The plants may contract differentially in response to available water, but whether this is a response/cause to temperature cannot be determined from this experiment. Only an association. Therefore, it has nothing to do with warming temperatures.
Phil. says:
Fine. Then plants that had contractile roots that pulled them into the soil at rates of 6-30 mm/yr survived to reproduce, those that didn’t, did not.
This isn’t “Little Shop of Horrors”, the plants are not going to start talking and/or strategizing their survival…
Mike Haseler says:
November 26, 2010 at 8:19 am
That was a very interesting article … thought provoking … surprising about rocks being cooler … more please!
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the Permaculture books have sections on Aridland gardening.
in Aus and elsewhere using rocks around the base of plants helps keep the soil cooler and enhances moisture retention, in winter the rocks warm up and help stop frost damage and keep a little warmth in the soils longer at night.
soil temps too hot to walk on is common in aus, a 40 C day will sure burn your feet while trying to get to the water at the beach:-)
or even walking round suburban dirt patches as I know, that why the national shoe is the thong! airflow and protection (aka chinese safety boots:-)
Wonder if they would do that while fully hydrated but exposed to high heat. I think not. Life is filled with unintended side benefits of both good and bad events. Dehydrated roots (not a healthy thing to have happen) will contract because they have less water in the roots, everybody knows that. As a result, deeply rooted plants will sink a bit into the ground as the contraction pulls them downward. Some species may survive under these conditions, while others will dry up on the surface.
My grandmother’s hens and chicks would do that, dry up on the surface. They would just be laying on top of the soil, with roots all dried up. But in the Spring rain and warmth, they would somehow rejuvenate and send roots down again.
Hardy little buggers.
Amicus, finally someone else who refers to those things as the real thong. That’s what we called them when I was a little girl. Nowadays, if you go to the department store looking for a pair of thongs, you are sent to the lingerie department.