- Written by: Tom Stapleton
In the fall of 2016, UC Davis Botany Graduate Student Zane Moore discovered that albino redwoods in the wild held twice as many toxic heavy metals compared to correlative green needles.1 This discovery led to intriguing questions like: do albino redwoods serve a purpose for the species by storing heavy metals in their needles? Are they removing contaminants from the soil and converting these toxins into non-soluble forms in order to clean up the forest?
In the plant world, they're many species that are known ‘hyperaccumulators’. These are trees that have the unique ability to concentrate high levels of heavy metal pollutants within their foliage & roots. The process of removing these toxins from the soil and binding them up in non-soluble forms is known as ‘phytoremediation’. Many species have the natural ability to clean heavy metal pollutants from contaminated environments. There have been groundbreaking studies in the US & other parts of the world where trees have been used specifically to cleanse heavy metal toxins from the soil. For example, poplar trees in Silicon Valley California have been grown to clean up toxins at superfund sites.2 Willow trees in Finland and Russia have been used to successfully clean up heavy metal toxins from mining areas and landfills.3
With phytoremediation being a possibility of why we see albinism in coast redwoods, Botany Ph.D. graduate student Zane Moore helped craft an experiment for Arborist Tom Stapleton in late 2016 to answer some of these questions. Combining Stapleton’s propagation experience with rare albino redwood chimeras with Moore’s expertise in the field of botany, both men wanted to know if there was a link between albino redwood growth & the specific heavy metal nickel. Some of the questions raised:
• Are redwoods producing more albinism when exposed to nickel?
• Does albino redwood growth point to phytoremediation?
• Can albino redwoods thrive in a high nickel environment?
• Will nickel produce more overall growth in these trees?
• What toxic effects does nickel exhibit within albino chimeras?
Based on Moore’s 2016 toxicity study on albino redwoods, nickel appeared to be one of the heavy metals most prevalently found in albino redwood foliage.1 With these findings, nickel was selected to be the heavy metal of choice for a three-year study.
A little back story on the metal:
Nickel was first isolated and classified as a chemical element by the Swedish chemist Axel Fredrik Cronstedt in 1751. The name ‘Nickel’ was derived from the term ‘Kupfenickel’ which means ‘Old Nick’s Copper’ that the German miners gave to niccolite because it emitted toxic fumes when heated.4,5 It wasn’t until a century later during the industrial revolution of the1800s that nickel was put to use in the form of coins around the world. The metal was prized for its corrosion resistance and being plentifully available. As technology increased throughout the 20th century, many new uses with nickel were employed. Modern applications for the metal include batteries, electronics, & electroplating. In addition, nickel has been widely used in the production of bathroom fittings, consumer white goods, food processing, manufacture of cables, wires, fasteners, motor vehicles, jet turbines, shipbuilding, surgical implants, and textiles.4,6 Airborne sources of nickel also became prevalent during the same period in the form of combustion of coal, diesel oil, fuel oil, and the incineration of industrial waste. 4,7,8,5 In some manufacturing sites’ emissions of nickel amounted to more than 100 times that of natural sources.4,9 As nickel uses expanded, soil contamination in the form of Industrial waste materials, lime, and sewage sludge became a major source of nickel pollution in the ground.4,10 The distribution of phosphate fertilizers on crops, has become another nickel pollutant source that has health implications by entering the food chain.4,11,12
Aside from manmade influences, nickel is found naturally in most soils around the world. In California and certain parts of the redwood range, nickel can be found in toxic levels within a soil type known as serpentine. This greenish-gray rock that sometimes resembles jade contains high concentrations of other toxic metals including chromium, cadmium, copper, lead, iron & cobalt.13 In addition to its toxic effects, serpentine is a nutrient-poor soil and has a very low calcium-to-magnesium ratio. It lacks many essential macronutrients like nitrogen, potassium, & phosphorous (NPK) essential for plant growth. Most plant & tree species find serpentine inhospitable to grow in. Only a select group can tolerate the difficulties the soil presents, examples are: California Bay Laurel- ‘Umbellularia californica’, Gray pine- ‘Pinus sabiniana’, & California Redbud- ‘Cercis occidentalis’. Some plants that have acclimated to serpentine soils have become specialized hyperaccumulators of heavy metals. Noccaea fendleri (Fendler's penny grass) is an example and has adapted to the harsh conditions that this soil brings.14 If these difficulties weren’t enough, serpentine becomes a carcinogen hazard to humans when its dust becomes airborne. It contains various amounts of chrysotile asbestos which is responsible for mesothelioma cancer.
Crafting the experiment:
With nickel handily selected as the toxic metal of choice for the study, it was time to select test subjects. Wild albino redwoods were ruled out for obvious reasons due to nickel’s potentially toxic effects on the environment. Instead, three periclinal chimeric albino redwood cultivars were selected for a controlled greenhouse experiment. All three cultivars originated from Forester Dale Holderman’s 1976 albino redwood cross-pollination experiment and are now known as USPTO patented trees: ‘Mosaic Delight’, ‘Early Snow’, & ‘Grand Mosaic’.26 The albino chimeras originated from the same patrilineal lineage exhibiting albino and green foliage similar to albino redwoods found in the wild.
2020 Chimeric Albino Redwood Nursery.
The growth patterns of the Holderman Albino Chimeras (HAC) were found to be remarkably similar to albino redwoods seen in the natural setting. Like their forest siblings, these propagated subjects express their initial growth with normal green foliage. Later after a rest period do the HAC trees develop albino growth. Within these chimeras, mutated & nonmutated foliage develops during two distinct growth cycles within a given year. The first initial growth seen occurs within the apical meristem (vertical leader) and lateral branches. This first expansion is known as ‘sylleptic growth’ and occurs without a rest period. Specifically, on the HAC trees, sylleptic growth is almost entirely expressed with green foliage. The second form of expansion occurs after a rest period and is known as ‘proleptic growth’. This type of expansion can be seen in axillary & accessory buds forming new albino secondary branches. See figure #4 for sylleptic and proleptic visuals.
Almost all the albinism produced within HAC trees comes in the form of ‘proleptic’ (secondary) growth. Past research has shown that 99% of all proleptic growth within these trees produces albinism. On the other hand, only 1% of all sylleptic growth produced albinism.15 When comparing the HAC tree’s morphology to natural redwoods, one can visualize a mature redwood producing both green sylleptic & proleptic growth in the canopy. Down at the base where the burl is located, water sprouts can be seen producing proleptic growth in the form of albino shoots. It was these distinct characteristic similarities between wild and cultivated albino chimeric redwoods that made the HAC trees ideal candidates for the experiment.
In January 2017, a total of 18 HAC trees were selected & planted into one-gallon pots for the study. Each tree was approximately two years old and about 30 cm (1 foot) in height. From the 18 HAC trees, three groups consisting of 6 trees each were given various treatment regimens of nickel sulfate hexahydrate. The first group was the control which received nickel-free water. The second group was administered 50 ppm nickel treatments, while the third group was given 100 ppm doses. Depending on the time of year, temperature, and evaporation rates, the amount of fluid given varied. All three groups though received the same amount of fluid per treatment.
A visual illustration of how each albino chimeric redwood was separated into testing groups. For example, starting from left to right, Control 1/Cutting #1 was labeled as C1/C2 & Treatment 3/Cutting #4 was labeled as ‘T3/C4’.
Within each treatment group of six trees, a sub-group was created to separate which trees would be allowed to produce proleptic (secondary) albino growth, while the others were not. Each subgroup consisting of three trees was tagged with a color marker. The ‘red’ subgroups were allowed to produce albino growth, while the ‘blue' subgroup had their albinism pruned upon emergence. The goal of creating the color groups was to observe green foliage growth rates and to determine if any differences could be seen between the two groups.
The only albino exception within the blue group was for sylleptic growth which formed the supportive structure of the tree and was left for stability purposes. As in the 2017 study, less than 1% albinism formed on sylleptic growth during this experiment and was subsequently not included in the study.
Figure # 5
This picture was taken in 2017 during the first year of the experiment. Note the new green sylleptic growth on these individuals.
During the study, all subjects were exposed to various levels of humidity and temperature as the greenhouse was not climate controlled. Humidity ranged as low as 10% in summer to 100% in Winter. Temperatures ranged from a low of 18 F° in winter to a high of 106 F° in summer.
Experiment Conclusion and Data Gathering:
In early January of 2020, the nickel experiment was concluded after 100 treatments were administered during the three-year study. Each tree received a total of 22.15 liters/ 5.85 gallons of water over the course of the experiment. Depending on the time of year and moisture needs, each treatment ranged anywhere from 100-350 ml. The average treatment consisted of 221.5 ml/ 7.49 oz of water every 11 days. Sixteen of the eighteen trees used in the experiment successfully survived the nickel toxicity trial. Two trees turned pale & died 6-7 months into the study as seen in figure #6.
A foliage census was performed on each of the surviving 16 HAC trees analyzing how much green and white growth had occurred. Branches & stem lengths were carefully measured and tabulated. This process which took approximately 64 hours to complete was the most time-consuming element of the project. The combined length for all trees equaled: 119.14 meters or 390.87 feet. For trees: T2/C3 & T3/C6 which died early in the experiment, a factored average of height & growth was calculated between the surviving members within each respective color & treatment group.
Chart #2 illustrates the percentage of albinism and green foliage produced within all red treatment groups.
Red Group percentage of green & white growth: When viewing the percentages produced across all red groups, chart #2 indicates a wide amount of variation. While the 100-ppm group exhibited the most albinism at 65%, no clear pattern could be established between all treatment groups showing a corresponding percentage rise of albino foliage the higher the nickel treatments were administered. The red control group showed a ratio of 57% albinism to 43% green foliage while the 50-ppm red group produced a slightly higher amount of green foliage at 56% to 44% white. A large decrease in the percentage of green growth was seen in the 100-ppm group with a ratio of only 35% green to 65% white.
Surviving foliage: Surprisingly almost half of the albino proleptic growth (48%) within the control red group died. This percentage lowered to 15% in the 50-ppm group and climbed back to 35% within the 100-ppm group respectively. Similar to the percentage of albinism produced, the pattern of dieback was highly variable. The average amount of dieback across all three red treatment groups equaled 33%. The only consistent pattern within this field was the low mortality of green foliage. Dieback was around 2% for both the control and 50 ppm groups. The 100-ppm group exhibited no green foliage dieback on any subjects for the duration of the three-year study. This data suggests that the two subjects who died early in the experiment may have failed due to causes other than nickel toxicity.
Chart #3 illustrates growth across four categories: Total Tree Height, Total White Branch Length, Total Green Branch Length, Total Tree Length.
Total Tree Height Data:
When comparing both the blue and red groups' tree heights, it wasn’t surprising to see that all red groups fell below those of the blue groups. The combined blue treatment groups averaged 29% taller than that of the combined red treatment groups. When comparing color & treatment groups side by side, the control blue group was 40% taller than the red control group. The 50-ppm blue group was 11% taller than the red 50 ppm group. The 100-ppm blue group was 35% taller than the red 100 ppm group. It appears albino foliage within the red groups reduced the tree’s vertical height potential by 29% overall. Another interesting discovery with the data showed a height average of 269 cm for the 100-ppm blue group, while the lowest was 138 cm for the red control group. This marked the greatest difference between heights by approximately 49%. There was a slight increase of 15% vertical growth on the blue 100 ppm trees compared to the blue control group. This appears to indicate that the blue trees may have benefited slightly from increased doses of nickel.
Total Growth Data:
Blue: In chart #3, trees within the blue group showed a marked increase in green growth the higher the nickel treatments were administered. In two areas of measurement: total branch length & total tree length showed increases starting from the control to 100 ppm groups. The only exception what a slight decrease in the total tree height between the blue control and 50 ppm group. Overall, the pattern showed a consistent increase in growth for the blue groups.
Red: As for the red group, albino growth was more variable between the control and 100 ppm subgroups. The control total white branch count was 1085 cm, while the 50-ppm group was the lowest at 959 cm. What’s interesting was the 100-ppm group demonstrated the highest amount of growth out of all the groups at 1684 cm suggesting that more overall growth could be produced the higher the nickel doses are administered. Another factor taken into consideration was the amount of proleptic regrowth produced by these trees when comparing the percentage of the foliage that was alive and dead at the end of the experiment. See chart #2 for percentage ratios of live and dead albino growth.
Only when the total tree length was calculated for the red groups did a clear pattern emerge showing a consistent increase in overall growth the higher nickel treatments were administered.
Chart #4 shows the total combined growth for Blue & Red in each treatment step:
When reviewing the total tree length within each color & treatment group, two patterns started to emerge. In both color groups, the higher the nickel treatments administered, the greater the amount of growth seen. The ‘control’ exhibited the lowest amount of overall growth, while the 100-ppm group exhibited the highest. Blue and red 50 ppm groups saw an increase of 9-12% over the control, while the 100 ppm groups saw a further increase of 18-23% over the 50-ppm groups. The growth band between the color groups showed distinctly that the red groups produced on average 25% more foliage compared to the blue groups. Interestingly when reviewing the growth gap between blue and red groups the percentage narrowed the higher the nickel treatments were administered. For example, the blue/red control growth gap was 28%. That narrowed to 26% between the blue/red 50 ppm and narrowed further to 20% within the blue/red 100 ppm groups.
Chart #5 light green columns indicate cutting weights in 2017 while the darker green columns represent cutting weights after the experiment concluded in 2020. Columns are highlighted by the color group for clarity.
Tree Weight Data:
At the beginning of the experiment (with all soil removed), each cutting weighed approximately 27.4 grams. The 100-ppm red group averaged the least at 22.5 grams while the 100-ppm blue group weighed 29.5 for a slight difference of only 2.1 grams. At the end of the experiment, the combined blue treatment group's weight total was =765.0 grams heavier while the red combined treatment group total was 459.6 grams heavier. For trees: T2/C3 & T3/C6 which died early in the experiment, a factored weight average was calculated between the surviving members within each respective color & treatment group.
The blue group produced 305.4 more grams of weight than the combined red groups. Even though the combined red groups produced more foliage than the combined blue groups, the red exhibited an average of 31.5% more dieback compared to the blue groups. Had this foliage been alive, its weight would have been closer to 604.1 grams. Hypothetically, this weight separation gap between the blue and red groups would have been narrowed by approximately 160.9 grams. With those theoretical numbers factored in, the blue groups still would have prevailed in the weight category.
After reviewing the weights of each color & treatment group three patterns were found:
• Both the blue/red 50 ppm groups exhibited the heaviest overall weight. Red came in at 238.5 grams while blue was 332.5 grams. The separation between the two-color groups was 94.0 grams.
• The weight gaps increased the higher the nickel treatments were given: red control was 23% lighter than blue control. The 50 ppm red group was 28% lighter than blue 50 ppm and the 100 ppm red was 54% lighter than blue 100 ppm.
• The combined red group weight was 544.5 grams while the combined blue group weight was 844.5 grams. The red group was 36% lighter than blue.
Chart #6: Numbers on light purple columns represent pH while the numbers on the dark purple columns represent ppm nickel present.
Soil Nickel Concentrations ppm Data:
All 100-ppm trees received 9.92 grams of nickel hexahydrate throughout the experiment. Of the 9.92 grams of nickel sulfate hexahydrate given only or 2.21 grams (22%) amounted to pure nickel. At the conclusion of the experiment, trees were removed from the posts and weighed. Soil pH was tested with ion test strips. For nickel ppm determination, 200 ml of equal parts water to equal parts potting soil was mixed and allowed to settle for 24 hours. This was done to allow all residual nickel in the soil to be fully dissolved in water. The highest results found were within the 100-ppm blue group at 23.3 ppm nickel. Hypothetically if no Ni absorption was made within the trees, the concentration of the Ni within the soil should have been substantially higher. For example, the 2.21 grams of Ni given over the course of the experiment x 1000 ml of water = 2210 ppm. Lower the amount of water to 200 ml (residual amount held in each pot) and you have a concentration increase of 5 to 1 or 11,050 ppm nickel. This suggests that almost all the available nickel was absorbed by the plants.
There was a steady decrease in pH noted between all three treatment groups. The control had the highest pH at 6.8 with the 50 ppm Ni group averaging a pH of 6.1. The 100 ppm Ni treatment group exhibited the lowest pH at 5.8. Nickel sulfate hexahydrate used in the experiment has a pH level of 4.5 which most likely contributed to the lowering pH values.
Results and Discussion:
After sifting through the data & analyzing the charts created, several unexpected morphologic patterns started to appear.
Total Tree length Findings:
A pattern did emerge in this category showing more overall growth the higher nickel dosages were administered. In chart #4 there was an average increase of 9% per treatment step for the red groups and a 12% increase per treatment step within the blue groups. The increase however was attributed to the incremental growth rates of green foliage within the blue groups compared to the red. In addition, this growth pattern also corresponded to a lowering of soil pH the higher nickel ppm treatments were given. In chart #6 we saw a pH drop from 6.8 to 5.8. Looking at the broader picture, past studies on legume crops have shown similar results showing a soil pH drop from 6.6 to 6.4 when treatments were increased from 0 to 90 ppm.16 This is because nickel availability in soils increases as the pH level decreases.17 In 1946 an English study on foliar application of nickel showed the first evidence that nickel significantly increased harvests of potato, bean, and wheat.18 More recent studies from 2007 have shown increases in size, weight, and fruit quality with soybeans, tomato, & parsley after foliar applications of nickel were applied.19 Why may we be seeing a link between increased nickel, increased growth, & lower pH values in the HAC trees? The answer may lie in what is known as ‘nitrogen fixation’. This is a chemical process by which molecular nitrogen from the air or elemental source is converted into ammonia or related nitrogenous compounds in soil. Nitrogen is one of the most vital components for plants in producing chlorophyll. Nickel although in smaller amounts plays an essential role in enzyme development with nitrogen-fixing bacteria.19 The lower the soil pH, the greater the capacity redwoods have to available nitrogen, nickel, and other essential micronutrients. Also, pH is the primary factor that controls heavy metal adsorption and their availability to these plants.20 Conifers like Coast Redwoods thrive in soils where pH levels range from 7.5 to 5.0, with 6.5 being the optimum.21 In addition, the nickel sulfate hexahydrate used in this experiment has a pH value of 4.5 which also contributed to the nickel available to the HAC trees. These combined factors may be the reasons why increased growth within the HAC test group was observed. Also, an article from the University of Florida Horticultural Sciences Department states: “Although there are still many unknowns regarding the functions of Ni in plants, it is known to be an irreplaceable constituent of the urease enzyme. Urease—whether produced by plants, microbes, or animals—contains nickel at the core. The urease enzyme is essential in converting urea to ammonium (NH4 + ). Thus, nickel is required in the nitrogen (N) nutrition of plants”.22 There’s also supportive evidence showing that nickel supports disease suppression as well.19 Surprisingly, it wasn’t until 2004 that nickel was recognized as one of the last elements by the American Association of Plant Food Control as essential for plant growth and development.22 This affirmation further supports nickel’s beneficial roles in plants.
Vertical Growth Findings:
The results in this category for the HAC trees were mixed. In chart #3 there wasn’t a clear pattern within each color group to suggest that there was a stepped increase in height the higher nickel treatments were administered. The combined blue treatment groups however were 29% taller than the red treatment groups. This was attributed to the fact that red HAC trees had less photosynthetic capacity compared to the blue groups. In contrast, within the ‘total tree length’ category there was an average of 25% more growth on the red groups than the blue due to the presence of albino foliage. When analyzing all red groups, the 100-ppm treatment group held the highest amount of albino foliage at 1684 cm. This high number may have been attributed to nickel but it was undetermined due to this column appearing as an outlier compared to the rest of the data set.
While the benefits of nickel as a micronutrient in this experiment were apparent across all blue treatment groups, there was evidence pointing to nickel & other elements creating a toxic environment within albino foliage. Throughout all red treatment groups, there were substantially higher rates of mortality within the albino foliage compared to green as seen in chart #2.
Since the control group exhibited the highest mortality at 48%, it was undetermined whether nickel was definitively a toxic contributor or beneficial agent in reducing the amount of albino foliage death. What’s known though through Stapleton’s past experiments with the HAC trees is albino foliage dieback occurs within 3-7 days after being treated with fast-release macronutrient fertilizers. Specifically, those containing high levels of NPK (nitrogen-phosphorus-potassium) within the 24-8-16 range. Concurrently while albino foliage showed signs of dieback, new green foliage emerged exhibiting growth without any ill effects. It’s hypothesized the reason for such a large disparity between albino and green foliage lies in the redwood’s ability to process macro & micronutrients. Because albino foliage cannot utilize these minerals through photosynthesis, they build up concentrations within their foliage that become phytotoxic. A 2012 study on albino redwoods found transpiration rates were more than twice as high as their green counterparts. Also, the study found that albino foliage exhibited poor stomata control regulating moisture loss.23 These combined factors further point to a more rapid accumulation of minerals within albino foliage compared to their green counterparts. In 2016 Botany Ph.D. graduate student Zane Moore confirmed this theory by discovering albino foliage held more than twice the amount of nickel, cadmium, & copper compared to green foliage. He also hypothesized that albino foliage’s uptake of nickel could be a possible mechanism for increased absorption of many other micronutrients as well. Moore also suggested that albino foliage could be a repository for heavy metals, therefore, benefiting the rest of the tree through phytoremediation.1
Circling back, we see that the majority of nickel administered in the HAC trees was absorbed into the plants. In chart #6 we detected that there was very little nickel remaining in the soil. The lowest was 3 ppm in the 50-ppm blue group and the highest was 23.3 ppm in the 100-ppm blue treatment group. What’s also interesting is the 100-ppm red group soil tested in at 12.5 ppm nickel compared to the 100-ppm blue group which almost double at 23.3 ppm. The difference between the two suggests that albino foliage most likely absorbed nickel more readily compared to green foliage. This and would be in line with what was found in the 2012 albino redwood transpiration rate study. Additional studies support that nickel is soluble & readily translocated within plants as pH levels decrease.22
Even though this study showed evidence of an interrelationship between growth and nickel ppm given, the threshold where phytotoxicity initiates within HAC trees wasn’t clearly defined. The two trees that died early in this experiment appear to have failed for reasons other than nickel toxicity. This is because more subjects would have been expected to fail the higher nickel concentrations became as the experiment progressed. In other plant species the level where phytotoxicity is highly varied. Foliage concentrations of nickel greater than 10 ppm are considered toxic in sensitive crop species. Nickel becomes toxic in moderately tolerant species at concentrations greater than 50 ppm. Some species can tolerate nickel concentrations in plant tissue as high as 50,000 ppm. There are some 350 species of trees known as “hyperaccumulators”, which are defined as plants that can accumulate at least 1,000 ppm Ni without phytotoxicity.17 The most common symptoms of nickel toxicity are the inhibition of growth, induction of chlorosis, necrosis, and wilting.24 Nickel concentrations in most plant leaf material normally range from about 0.1 to 5 ppm but can be highly variable depending on its availability in soils, plant species, plant part, and season.17 To determine a baseline of what nickel levels were found within HAC albino and green foliage, spectrometry testing will need to be conducted as a second phase to this study to determine if albino redwoods are true hyperaccumulators of nickel.
In this final category, we see that both the red and blue 50 ppm groups held the highest overall weight ratios. This suggests that the 50 ppm treatments may have been the optimum level of growth, balancing between nickel’s beneficial role as a micronutrient to its side effects as a toxic contributor to the environment. Also, the 50-ppm red treatment group saw the least amount of albino mortality at around 15% as seen in chart #2. In the same chart, we see that the 50-ppm red group also held the highest percentage of green foliage at 56%. The 50-ppm blue group held the highest weight at 332.5 grams indicating this may be the optimum level to promote growth. Interestingly the weights in both red & blue groups decreased with the 100 ppm treatments. The highest reduction was between the red 50-100 ppm red group at 45% and the lowest reduction between the blue 50-100 ppm groups at 14%. Another pattern found was the higher the nickel treatments were administered, the larger the weight gap became between the red and blue groups. For example, the red control was 23% lighter than the blue control. The 50-ppm red was 28% lighter than blue 50 ppm and the 100-ppm red was 54% lighter than blue 100 ppm. This suggests that the accumulation of nickel within the plants had an adverse effect on root development, not just the foliage. Since the majority of the dieback occurred within the red group, their combined tree weights were approximately 60% lighter than the combined blue groups. Had all the albino foliage remained alive on the red groups, the factored weight would have been reduced to 29%. Another pattern found in the trend lines between chart #2 & #5 shows a correlation between the amount of green foliage present is proportional to the amount of weight seen within the red groups HAC trees. With the data indicating higher weight percentages within the blue groups, there wasn’t any discernable difference with root size between all color and treatment groups.
Naturally Occurring Nickel, Balancing the Good and the Bad:
Applying the experiment findings to redwoods in the wild, there may be benefits seen with increased nickel levels than first understood. Coast Redwoods thrive in alluvial & silty loam soils that exhibit an abundance of macro & micronutrients. But in transition zones where serpentine soil interacts with other soil types may increase nickel levels to where they become useful to redwoods. The Coastal Range where the species is native is known to hold various loose soil types. The combination of structurally weak soil & high annual rainfall produces large amounts of erosion throughout the range. This geologic mixing allows different soil types to interact and amalgamate in river drainages. Alluvial flats may form complex soils where redwoods can utilize safe levels of nickel to their advantage.
Nickel & Anthropogenic Effects with Redwoods:
As human development expands further into our forestlands, it comes as no surprise that we’re seeing increased numbers of albino redwoods in these areas. Years of research exploring albino redwood sites have shown that these mutations are occurring at higher rates along the wildland-urban interface. Human activity in the form of, asphalt petroleum, fertilizers, insecticides, creosote from railroad ties, & septic systems are leaching toxins and other heavy metal contaminants into the soil. These could be the reasons why we’re seeing the formation of these mutations. For example, albino redwood sites within California’s Central Valley were virtually unheard of before 2012. As of this writing (2021), there are approximately 100 documented sites where aerial albino redwoods have been discovered throughout Central Valley. Like cancer clusters, certain neighborhoods within the Sacramento region hold more albino redwoods per square mile than Redwood National Park. Redwoods being a genetically complex species may be warning us through these mutations that airborne and soil contamination may be linked to human and redwood health concerns.
Conclusion & Tying it Together:
While the size of this experiment was a small sampling compared to the hundreds of albino redwoods in the wild, it was promising to see that nickel may have played a beneficial role for green foliage production within the test subjects. This seemed to have the opposite effect on albino foliage which showed a higher propensity for dieback at various amounts of nickel treatments given. Also, the amounts of nickel given appeared to be below the toxic thresholds that the species could tolerate within green foliage but were mixed within albino foliage. The experiment did show an increase in overall growth the higher nickel treatments were administered. The opposite occurred in the weight category where lower overall values were seen the higher nickel treatments were administered. The 100 ppm red group showed the highest increase in albino redwood foliage despite increases not being linear across all three red treatment groups. Even though definitive evidence wasn’t found pointing to a correlation of increased albino growth to a ratio of nickel treatments given; the results within the 100-ppm red groups showed the possibility for a different outcome within a larger study. The small scale of this experiment may have yielded highly variable results making another experiment warranted. A follow-up study with higher nickel concentration levels may give more definitive answers if albino redwoods are truly phytoremediators. A limiting factor to the experiment’s size and scope was the scarcity of test subjects, available resources for advanced soil and foliage testing. Despite these limitations, these preliminary findings were encouraging and may open the door to future discoveries for the redwood species.
I would like to thank the Holderman Family for making this study possible through the chimeric albino redwoods produced by the late Forester Dale Holderman. I also appreciate Zane Moore for his expertise in crafting the experiment, my family who patiently endured many hours of research, the cited work that supported these findings, and all those who have supported my ongoing efforts with albino redwood studies.
1) Albino leaves in Sequoia sempervirens show altered anatomy and accumulation of heavy metals Zane J. Moore, Department of Biology, Colorado State University, Fort Collins, Colorado, 80523-1878, USA;
2) New York Times article 4/7/2020 titled: Superfund, Meet Super Plants Can the plant microbiome help clean up contaminated land? https://www.nytimes.com/2020/04/07/science/superfund-plant-microbiome.html
3) Science Daily article 12/12/2014 titled: Willow trees are cost-efficient cleaners of contaminated soil https://www.sciencedaily.com/releases/2014/12/141212084952.htm
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8) McGrath SP (1995). Nickel. In: Heavy metals in Soils. Alloway, B. J. (Ed). Blackie Academic & Professional, London.
9) Nriagu JO (1990). Global metal pollution poisoning the biosphere? Environ., 32: 7-32
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13) Chiarucci, A., Baker, A.J.M. Advances in the ecology of serpentine soils. Plant Soil 293, 1–2 (2007). https://doi.org/10.1007/s11104-007-9268-7
14) Harrison, Susan; Rajakaruna, Nishanta (2011). Serpentine : the evolution and ecology of a model system. University of California Press. ISBN 9780520268357. OCLC 632224033.
15) Stapleton/Moore chimera albino redwood foliage census. Unpublished work 2017.
16) Paper: 2/06/2017 Ramez Saad, A. Kobaissi, Christophe Robin, Guillaume Echevarria, E Benizri. Nitrogen fixation and growth of Lens culinaris as affected by nickel availability: A pre-requisite for optimization of gromining. Environmental and Experimental Botany, Elsevier, 2016, 131 (Environmental and Experimental Botany), pp.1-9. ff10.1016/j.envexpbot.2016.06.010ff. ffhal-01458433f
17) International Plant Nutrition Institute Article 16
18) Roach, W. A., and C. Barclay. 1946. “Nickel and Multiple Trace Deficiencies in Agricultural Crops.” Nature 157:696.
19) Paper: April 2011 Miguel Ángel López1,3 and Stanislav Magnitskiy. Nickel the last of the essential micronutrients:
20) Harter, R.D. (1983), Effect of soil pH on adsorption of lead, copper, zinc, and nickel. Soil Sci. Soc. Am. J.,47, 47-51.
21) Paper: Zinke, Paul J.1964. Soils and ecology of redwoods. In, Forestry Seminar Series, Fall-Winter, 1964. Univ. Calif. Agr. Ext. Serv., pp. 26-44, illus.
22) Paper: Horticultural Sciences Department, UF/IFAS Extension June 2011 Nickel Nutrition in Plants1 Guodong Liu, E. H. Simonne, and Yuncong Li2 https://edis.ifas.ufl.edu/hs1191
23) Pittermann J, Cowan J, Kaufman N, Baer A, Zhang E, Kuty D (2018) The water relations and xylem attributes of albino redwood shoots (Sequioa sempervirens (D. Don.) Endl.). PLoS ONE 13(3): e0191836. https://doi.org/10.1371/journal.pone.0191836
24) Toxicity of Nickel in Plants Satish A. Bhalerao*, Amit S. Sharma and Anukthi C. Poojari Environmental sciences research laboratory, Department of Botany, Wilson College, Mumbai 400007, M.S., University of Mumbai
25) Kotov V, Nikitina E (1996). Norilsk Nickel: Russia Wrestles with an old polluter. Environment, 38: 6–11.
26) Davis, D. F.; Holderman, D. F. (1 February 1980). The white redwoods: ghosts of the forest. Naturegraph Publishers.
- Written by: Tom Stapleton
In the fall of 2016 research colleague Zane Moore discovered that albino redwoods in the wild held twice as many toxic heavy metals compared to correlative green needles. This discovery: The mystery of the ‘ghost trees’ may be solved led to intriguing questions like: Do albino redwoods serve a purpose for the species by storing heavy metals in their needles? Are they removing contaminants from the soil and converting these toxins into non-soluble forms in order to clean up the forest?
In the plant world there are many species that are known as ‘phytoremediators’ which have the natural ability to clean heavy metal pollutants from contaminated environments. There has been ground breaking studies locally & in other parts of the world where trees have been used specifically to cleanse heavy metal toxins from the soil. For example: poplar trees in Silicon Valley California have been grown to clean up toxins at superfund sites. Willow trees in Finland and Russia have been used to successfully clean up heavy metal toxins from mining areas and landfills.
With phytoremediation being a real possibility of why we see albinism in coast redwoods, Tom Stapleton and Botanist Zane Moore teamed up to formulate an experiment in late 2016 to help answer these questions. Combining Tom’s propagation experience with rare albino redwood chimeras along with Zane’s botany expertise on phytoremediation, both men wanted to know:
• Are albino redwoods true phytoremediators?
• Do albino redwoods consistently have higher tolerance for heavy metals compared to green redwoods?
• Are redwoods producing more albinism when exposed to heavy metals?
• At what toxicity level do albino & green redwoods start experiencing stress?
• What specific heavy metal may be inducing albino mutations in redwoods?
Based on Zane’s 2016 toxicity study on albino redwoods, the heavy metal nickel appeared to be the element most prevalent at the various soil testing sites. With these findings, nickel was decided to be the toxic metal of choice for an ongoing 2-3 year study. Because chimeric albino redwoods both exhibit albino and green foliage within the same plant, they best represented albino redwoods found naturally in the forest.
Beginning in January 2017 in a controlled greenhouse environment, three groups consisting of young albino redwood chimeras were given various treatment regiments. The first is the control group while the other two are administered specific nickel doses. Depending on the time of year, temperature, & evaporation loss, treatment amounts are given equally among the groups.
With a little over a year into the study, some subjects have already turned pale and died. Their foliage and soil will be tested at the conclusion of the experiment in order to determine toxicity levels. The remaining subjects that have exhibited various rates of green & white growth will also have their data published at the conclusion of the experiment.
For more information on phytoremediation and the benefits of using plants to clean toxins see links below:
Willow trees are cost-efficient cleaners of contaminated soil