| BEN |
| BOTANICAL ELECTRONIC NEWS |
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| ISSN 1188-603X |
| No. 245 March 23, 2000 | aceska@freenet.victoria.tc.ca | Victoria, B.C. |
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Professor Emeritus of the University of Washington in Seattle, on the occasion of his 80th birthday, March 21, 2000. His name does epitomize the Pacific Northwest botany. All the best, Art!
[APOLOGIES: I am sorry I mispelled Dr. Richard Walker's name in his article "Arthur R. Kruckeberg -- Active octogenarian" in the last BEN. Dr. Walker is Professor Emeritus at the University of Washington and a close colleague of Dr. Art Kruckeberg. I apologise to him and to the readers. - Adolf Ceska]
I spend a certain amount of time bring natural history to the hoi poli via a weekly 3-4 minute radio spot on southern Oregon's National Public Radio Station, Jefferson Public Radio. Subjects vary from dust mites to Darlingtonia, and often include vignettes of notable botanists. In 1990 I helped Art Kruckeberg celebrate his retirement from the University of Washington. Ten years later, Art is still very active and about to celebrate his 80th birthday. What follows is the script of that radio spot broadcast 10 years ago.
"May 18, 1990, students, friends, and colleagues met at the University of Washington to pay homage to one of the Pacific Northwest's great outdoor botanists, Arthur R. Kruckeberg. The event? His retirement, at the age of 70, from the University of Washington after a distinguished career as an outstanding scientist and teacher."
"Professor Kruckeberg is known to many of you as the author of Gardening with Native Plants of the Pacific Northwest. Others of you may know him as one of the world's leading authorities on serpentine vegetation and flora. I knew him as my major professor while I was working on my Masters degree at the University of Washington."
"His gardening book is a must for anyone interested in cultivating our native flora. The book is beautifully illustrated with both color and black and white photographs and line drawings. The introduction includes discussions of plant names, the history of gardening with Northwest plants, natural environments including plant hardiness zones, and propagation techniques. With few exceptions, transplanting whole plants from the wild is discouraged. Grow from seeds, propagate from cuttings, or purchase from a reputable native plant nursery, but don't plough up the native habitat."
"For each species there is a discussion of ecology and distribution, distinguishing features and propagation methods with many interesting facts woven into the very readable text. Professor Kruckeberg's superb knowledge of the flora of the Pacific Northwest and his love for plants shines throughout the book."
"Serpentine, to botanists, has nothing to do with snakes. It has to do with a special soil type, that has an unusual mineral composition, high in magnesium and heavy metals like iron and sometimes chromium and cobalt and low in calcium. These unusual conditions account for many of the unusual plant species of southwest Oregon. For the past forty years, Art Kruckeberg's continuing scientific investigations have done much to explain the relationship between serpentine soils and their native floras. I have my plant ecology students read his early paper on the response of plants to serpentine as much for the simple, elegant, experimental methods as the answers they provide."
"I pay homage to him for the privilege of having been his student. What we are, as we progress through life, is the final distillation of those who influence us in various ways. I am grateful to the good professor for putting up with me through good moments and bad, and for being largely responsible, draft after thesis draft, for what meager writing skills I now possess. So I wish, for Arthur Kruckeberg, a long and fruitful retirement. I don't know why I was surprised to learn that Art was retiring at seventy. It was only 29 years ago that I was his student!"
"For Nature Notes this is your host Frank Lang."
Now it has been 39 years since I was his student. I continue to learn. Thanks, Art.
Professor Art Kruckeberg's romance with serpentine has made geologists realize that vegetation supported by this unique substrate has a unique evolutionary history of survival in a very hostile environment. Art has been a leader among a group of botanists-biologists-chemists-geologists-pedologists that are enhancing our knowledge of the strange flora found growing on "serpentines". This short note will show why these serpentine soils are so different and why they attracted Art's curiosity.
The Earth's mantle consists of peridotite (ultramafic rock) a dense brownish to black rock consisting of ferromagnesian silicate minerals. Continuous plate tectonic movements at the Earth's surface incorporated small masses of peridotite into continental margin sedimentary wedges. Peridotite instability in the presence of water at low temperatures leads to its transformation into serpentine minerals producing a green, light, and weak rock within the Earth's Crust. Serpentine rock has nearly the same chemical composition as peridotite except that it contains 13% H2O and is less dense. Serpentinization is usually not complete and highly variable leading to a great range in its physical appearance. Where there has been shearing, serpentine rock displays highly polished greenish-black surfaces.
On the surface of the Earth's Crust, peridotite and serpentine soils create a hostile environment for plants because of their inherent lack of nutrients required for plant life and a chemical composition rarely found for the Earth's soils. Chemically, serpentine soils developed in temperate climatic zones from serpentinized mantle peridotites have a Ca/Mg less than 0.7 and are extremely low in the essential nutrients Ca, K and P. Ni, Cr, and Co are concentrated during soil and laterite formation producing a toxic environment for certain plant species. Professor Hans Jenny referred to the strange soil composition as the "serpentine syndrome."
These high concentrations of chromium and nickel combined with very low Ca/Mg ratio in serpentine soils gives rise to the sparse vegetation having a unique floristic population. The abiotic aspects of peridotite-serpentine evolution are unique. Deep weathering of peridotite in tropical climates produces nickel laterite, our main source of nickel. Economic chromite concentrations are present in some peridotite and most of the commercial asbestos fibers are extracted from serpentine-peridotite rock. Ground water within peridotite-serpentine assumes unique compositions high in magnesium bi-carbonate and in some arid and semi-arid climates these waters exceed pH 11.5 as they become saturated with calcium hydroxide during near surface serpentinization.
Minor and trace elements in serpentine soils are concentrated in some plants that have adapted to the toxic chemical elements. Plants with concentrations of heavy metals greater than 1000 ppm are referred to as hyper-accumulator plants. These hyper-accumulator plants are of great interest to scientists trying to understand environmental pollution or fundamental plant evolution. Serpentinized peridotites contain about 0.3% of NiO concentrated mainly in the olivine and less so in the pyroxene. Nickel becomes available to plants by weathering of these silicates in the soil horizons especially in humid tropical climates. Many plants known to be hyperaccumulators of nickel occur on serpentinized peridotites. The high concentration of Ni in these hyperaccumulators is ideal for phytochemical studies involving mineral exploration, agronomy, and biochemistry. Other transition metals such as Co, Cr, Mn, and Cu are found in serpentine endemic plants but do not reach the elevated concentrations found for nickel. The phytoextraction of toxic metals in contaminated areas has become an important new tool for environmental remediation as a direct result of scientific studies on Ni-hyper-accumulators found in serpentine areas.
Recognition of the biotic and abiotic uniqueness of peridotite-serpentine tracts has prompted a worldwide agenda to preserve them as ecological islands of great scientific value. Future studies could well focus on the microbiotic populations to learn of their adaptation to serpentine soils. Genetic studies on the serpentine endemic plants may provide answers to plant adaptation in hostile environments.
I first became aware of plant life on serpentine soils in my second year as an undergraduate at College of the Atlantic, Maine when I wrote a term paper on the evolutionary ecology of plants on serpentine soils. That was when I first heard of Dr. Art Kruckeberg. In a short period of time I became completely fascinated with life on serpentine soils and the abundant opportunities these habitats may provide to study plant ecology, evolution, and physiology. Five years after writing the term paper on serpentine ecology I came in contact with Dr. Bruce Bohm at the University of British Columbia in Vancouver, B.C., who promised me an opportunity to get my hands dirty in the Californian serpentine.
My research, which began about five years ago, has been directed towards using goldfields, Lasthenia californica Lindley (Asteraceae) as a model system to understand the process of speciation under edaphic influence (Rajakaruna & Bohm, 1999). Lasthenia californica is the most widely distributed of the 17 species of this mostly Californian genus. Studies of L. californica have indicated the existence of two distinct races. I have documented strong edaphic preferences by the two races (A and C); they are physiologically differentiated, notably in their sodium physiology and root growth. Race A plants have the capacity to accumulate sodium to levels found in halophytes and have much larger root:shoot ratios than race C plants.
The physiological adaptations of race A plants possibly play a key role in the initial ecological isolation of the races. Greenhouse studies have shown that race C is unable to survive to reproductive maturity in the soils of race A plants. Although the races are generally found in allopatry they occasionally occur in sympatry. The largest known sympatric population is found on a serpentine outcrop at the Jasper Ridge Biological Preserve of Stanford University. Here, the races are restricted to the upper and lower reaches of the outcrop and maintain a sharp boundary that correlates well with changes in soil chemistry. Surprisingly, the boundary has not changed considerably in over 15 years.
Since Lasthenia plants are obligatory outcrossers and are pollinated by a variety of insects, there is opportunity for gene exchange. However, field observations and greenhouse studies showed that the races have reduced crossability. At Jasper Ridge, the flowering times between the races differ by seven to ten days. This phenology has been repeatedly confirmed in both field observations and greenhouse studies. Apart from this seemingly effective flowering time difference the races have a limited capacity to cross. A breeding study, using seven populations from the species' range, revealed that races can interbreed, but often with low seed production.
The sympatric races from Jasper Ridge have a very limited capacity to cross (4-7% seed set in an inter-racial cross compared to over 79% in an intra-racial cross). The level of crossability between allopatric populations of the two races was always higher than in the sympatric location. There are two possible explanations for this result: 1) Jasper Ridge represents the point of most extreme divergence between the races. Alternatively, 2) strength of reproductive isolation between races may indicate that reinforcement of reproductive barriers has occurred in this locality. Recent studies are showing that the barrier to inter-racial crossability at Jasper Ridge may be prezygotic where the pollen grains from one race are aborted on the stigmas of the other race.
The research conducted so far has revealed some interesting findings. The long-term study at Jasper Ridge is the first case where population differentiation has been documented within a serpentine outcrop. Our studies have also clearly documented that serpentine soil within the same outcrop can be very heterogeneous and that chemical and physical features can change drastically along an elevational gradient. The finding of sodium accumulation by a race growing on serpentine soils is also a new finding. Our hypothesis that the sodium is used as an osmoticum by race A, which dominates soils of extreme ion content will be tested in the near future. If proven correct this will be one of few studies to document a mechanism of adaptation to these harsh soils.
Besides my studies of Lasthenia californica, I have had the opportunity to visit four of the five serpentine outcrops in my native Sri Lanka. I have compiled a list of 54 species for these sites and have analyzed both the soils and the tissues of plants growing there. This is the first study of the serpentine sites in Sri Lanka. I have discovered three (possibly five) hyperaccumulators of nickel from these sites along with many other plants of taxonomic and physiological interest.
The more I become involved in serpentine research the more I understand why botanists like Art are so dedicated to the study of serpentines. Serpentine outcrops offer so many puzzles and to a keen botanist there will always be so many unanswered questions. I am sure Art has never got bored trekking the serpentines of the Pacific Northwest and the rest of the world. It is amazing to think of the wealth of knowledge he has accumulated in his years of research, teaching, and keen observations.
I wish Art a very happy eightieth birthday and many more years of good health. I feel extremely privileged to have been able to write this very personal account in his honor. May his dedication and love for the world of serpentine inspire many others like myself, now and for many more years to come.
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