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.
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
4) Nickel in soils: A review of its distribution and impacts Yahaya Ahmed Iyaka Department of Chemistry, Federal University of Technology, P. M. B. 65.
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7) Clayton GD, Clayton FE (1994). Patty‟s Industrial Hygiene Toxicology. 4 th Edn., A Wiley- Interscience Publication, New York.
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.
Redwood enthusiasts who are lucky enough to know where these elusive albino redwoods reside have discovered that some of these peculiar trees tend to dieback and regrow in cyclical patterns. Some basal albino redwoods exhibit large amounts of leaf litter accumulation while others show very little accumulation. As if the albino redwood mystery wasn’t complex enough, some experts have suggested that this dieback & regrowth pattern occurs because the mutations are easily prone to environmental stresses. Specifically: heat, cold, and drought conditions appear to play a role in albino redwood mortality. Research at UC Santa Cruz has shown that albino redwoods do indeed transpire at much higher rates in summer compared to their green counterparts as seen here in this paper: The water relations and xylem attributes of albino redwood shoots These discoveries have led experts to speculate that albino redwoods overall may have inefficient stomatal control leading to excessive moisture loss and death within their needles. Stomata are pores on plant leaves that help regulate transpiration and water loss. In normal green redwoods, cool humid conditions will prompt stomata pores to open allowing for a greater surface area for transpiration to occur. Conversely, in warm weather accompanied by low humidity, stomata will close down to conserve water. The situation for albino redwoods is more problematic and appears to run counter to the normal function of the plant. In hot weather, if albino redwood stomatal cells don’t close down enough to limit moisture loss, the foliage will cavitate, wilt, and die. On the other hand, if temperature and humidity levels are ideal, but there isn’t a sufficient amount of sugars readily available from the parent tree, the mutation will dieback due to deprivation. This is a catch 22 situation that albino redwoods must face on a daily basis. Even when surviving in this precarious state, it’s not known if reliance on high transpiration rates is a definitive reason why there’s a tendency to see dieback on these trees. While it’s generally understood that all redwoods (whether albino or not) will experience some form of dieback under extreme moisture stress, it’s not known if the parent redwood is sacrificing the mutation at the expense of water or energy conservation.
Additionally, other seasonal factors like excessive heat, & freezing temperatures have led to further assumptions that albino redwoods may not have adequate coping mechanisms for extreme weather conditions.
Pictures of a basal albino redwood in the natural range. The photo on the left was taken in June 2012 while the one on the right was taken in June 2018. Notice how the albino redwood almost appears dead in 2012, only to return to a more vigorous state in 2018. Some may attribute this to the drought that was experienced between 2011-2016. If this is true, why do surrounding green shoots appear unaffected in both the 2012 & 2018 pictures?
If these reasons aren’t enough to show albino redwoods are at a real disadvantage, other factors such as fungal pathogens, insect damage, vandalism, and animal browsing can further add to the demise of these trees. Sudden oak death which has made headlines in the last couple of decades produces minor dieback on both green and white foliage. Various insects such as thrips and mites which are common in redwood forests attack redwood needles and discolor foliage. Visitors at times take albino foliage as souvenirs also adding to further losses. Deer which have been known at times to rub their antlers on young trees during the fall rut also contribute to additional damage. The culmination of these external causes doesn’t appear to add up to a cyclical pattern of dieback seen in albino redwoods, but can further contribute to their destruction.
With the culmination of the above, albino redwoods are indeed in a precarious position and must find a balance to survive. These disadvantages alone, make researchers question how these anomalies of nature can survive in an environment where the deck seems stacked against them. But are albino redwoods truly fragile mutations or robust warriors? Some may indeed exhibit poor stomatal control, but are they really at the mercy of the weather, or is there another factor at play pointing to albino redwood mortality? What advantages do healthy-appearing albino redwoods have over their counterparts and what can their life cycles tell us about the overall health of the redwood forests? These questions may seem daunting as if one was to begin tackling a 10,000-piece jigsaw puzzle. It seems current research is only now starting to piece together the outer edges of the mystery.
Cotati Tree Chimeric Albino redwood illustrating various mosaic patterns seen within these mutations.
To start putting the pieces into place, several key questions need to be asked and formed into a hypothesis.
Are albino redwoods fragile due to physiological, ecological, or environmental causes?
A) Are climate factors contributing to albino redwood dieback or longevity?
B) Does temperature variation affect stomatal control?
C) Can albino redwoods endure weather extremes?
D) What implications will these results have on the species?
Because naturally occurring albino redwoods in the wild are very rare, studying various groups of trees in the natural setting was deemed impractical for logistical & ecological reasons. The concern was to conduct a study that would yield the best possible answers, yet not leave the human footprint within the forest. To achieve this, a group of 25 propagated chimeric albino redwoods was selected & planted a test plot within the Central Sierra spring of 2017. Ten trees were initially planted in the ground with the remaining planted out over the course of summer. Trees selected for the study exhibited traits that were morphologically very similar to albino redwoods in the wild and ranged from 3-8’ in height. Both the wild & planted albino redwoods exhibit sectors that had mutated foliage supported by healthy green foliage. Observing the growth patterns with propagated albino chimeric redwoods allowed researchers the opportunity to see daily changes in a controlled setting that otherwise wouldn’t be possible with albino redwoods in the wild. Various chimeric albino redwoods from different parts of the natural range were selected for the study to gain a wider genetic sampling on how these chlorophyll deficient mutations would respond.
Seven-foot-tall chimeric albino redwood at the Sierra test site.
The location chosen for the test plot was well removed from the native range of Coast Redwoods by more than 100 miles. The site was situated in a lower montane forest at an elevation of approximately 3500’ elevation. The test plot’s climate fell within USDA hardiness zone 9a which exhibits average winter low temps between 20 to 25°F. At this elevation, snow is frequent in winter adding an element of stress to the trees that otherwise would not be seen regularly in the natural range. Summers exhibit hot conditions with temperatures frequently running from the low 90’s to the low 100’s°F. Additionally, humidity ranged only between 13-60% during the summer months. Some might consider this a hostile environment well beyond the scope of what would be seen in the natural setting. Because of these climate extremes, all trees were given supplemental irrigation during the summer months so as not to induce water stress. The experiment was looking for stomata control correlating to heat & cold tolerance in albino redwoods & not the test subjects’ ability to withstand drought stress.
During the summer of 2017, all subjects were exposed to temperatures of over 100°F. Daily temperature fluctuations averaged between 68-93°F per day and did not exceed a temperature swing of more than 30°F in a single day. By late fall of that year, remarkably only 5% of the albino foliage from the 2017 growth season exhibited some form of dieback. A modest 20% of dieback occurred on albino foliage that was two seasons or older.
Tree #14 originating from Santa Cruz County endures the full afternoon sun on July 29th, 2017. A nearby weather station recorded the daily high temperature at 98°F. Note how a majority of the albino foliage appears healthy despite the intense heat. The all-time high for the year was recorded a month later on August 28th, 2017 at 104°F.
This picture was taken after the trees were planted on Nov 3rd, 2017. Notice how little albino foliage has died back on tree #14 during the summer months despite days of temperatures over 100°F.
As winter approached, it was not known if the albino foliage would be as resilient to cold weather as it had with coping in the summer heat. February daily winter temperatures averaged between 55°F -35°F per day with humidity ranging between 35% & 85%. As with the summer results, the albino foliage on 90% of the test subjects exhibited cold tolerant characteristics unseen before in albino redwoods.
In the dead of winter, albino foliage appears mangy on Tree #14 but is otherwise healthy under the snow. The picture was taken on February 21st, 2018. Two days later on the 23rd, the lowest temperature of the year was recorded at 18.7°F.
Tree #8 originating from Sonoma County shows the contrast of albino & green foliage in the snow. At times, these trees were covered in over a foot of snow during the winter of 2017/2018. The picture was taken on February 18th, 2018.
The following spring, albino foliage on tree #14 survived remarkably well over winter with minimal dieback. The picture was taken on April 1st, 2018.
Close up of tree #14 in April 2018 showing foliage in excellent condition after enduring winter snow and ice. The picture was taken on April 1st, 2018.
A closeup of Tree #8 April 2018 exhibiting albino redwood foliage after surviving the winter of 2017 & 2018. Like tree #14, albino foliage shows almost no dieback after winter.
By spring of 2018, only 10% of year-old albino foliage exhibited some form of dieback from either heat or cold stresses on all test subjects. A more modest 30% dieback occurred on albino foliage that was at least two seasons or older.
If the weather environment at the Sierra test pot site exhibited temperature extremes higher and lower than what’s normally seen in the natural range, then why did these test subjects perform remarkably well during the heat of summer and cold of winter compared to their wild counterparts? One would assume that more needle dieback on the Sierra test subjects should have been seen compared to the naturally occurring albino redwoods along the coast. Another could argue that the test plot trees were given ample irrigation compared to the albino redwoods in the natural range which relies solely on fog drip and groundwater. If this truly was an unfair advantage, then why does normal green foliage on the parent trees to albino redwoods appear healthy when albino foliage started to dieback? The answer appears to indicate that redwoods may not exclusively be dependent on how much water is readily available, but how they respond & adapt to rapidly changing weather patterns.
To test the hypothesis that rapidly changing weather patterns are influencing albino redwood dieback, a comparison was made between the weather patterns at the Sierra test plot site to two locations within the natural redwood range. Specifically, the weather patterns at Guerneville in Sonoma County and Felton in Santa Cruz County were used in the study. The hottest three consecutive days in July 2017 were plotted and compared at all three sites.
Data courtesy of Weather Underground.
What's remarkable was the huge 24-hour variation in temperature and humidity reported by the Guerneville and Felton weather stations compared to the Sierra site. The trees within the Sierra test plot rarely experienced temperature shifts greater than 30°F per day and humidity changes of 33%. In contrast, the Guerneville and Felton sites exhibited temperature shifts greater than 51 degrees °F in a single day, accompanied by humidity swings exceeding 90% according to Weather Underground data. Cool onshore winds carrying low temperatures and high humidity during summer can quickly reverse to an off-shore weather pattern bringing low humidity and hot dry winds within a matter of hours. This yoyo weather effect induces stress on the native trees that otherwise would not be as pronounced in California’s interior. It’s plausible that in some individuals, the stomata within natural albino redwoods become overwhelmed in these conditions, leading to higher transpiration rates, cavitation, and eventual dieback. In comparison, the relatively dry Sierra Nevada test site provided a more stable temperature and humidity environment allowing for more efficient stomatal control in coast redwood albino chimeras.
A second temperature & humidity comparison was made for winter 2018 between the Sierra test plot site and the Guerneville & Felton locations. The coldest three consecutive days in February were plotted and compared at all three sites.
The winter trend lines for temperature and humidity appeared to follow a little more closely between all three sites compared to summer. Temperature fluctuations were less severe averaging a modest 32-degree °F swing at the Sierra site, 20-degree °F swing at Guerneville, & 21-degree °F swing at Felton. As expected, the Sierra site exhibited lower temperatures and humidity levels compared to the coastal locations. The humidity results showed a reversal in winter between the Sierra and coastal locations. The Sierra site showed the largest humidity swing of approximately 71% when compared to Guerneville’s 64%, & Felton’s 58% respectively. It’s speculated that the winter dormancy period combined with a lower variation of temperature and humidity may help preserve albino redwood foliage.
Stepping back and looking at the history of the Felton and Guerneville sites before the old-growth forests were removed; temperature and humidity changes most likely were more moderate during times of hot and cold weather periods compared to today. The dense stands of trees acted as a temperature and humidity buffer when rapidly changing weather patterns descended upon the forests. Because of these insulating properties, the trees created their own protective weather bubble by limiting moisture loss which is not seen at these sites today. Without the support of large tree stands, it’s assumed that the genetics of these individuals may not be as adaptive or tolerant to rapidly changing weather conditions as redwoods growing in more interior locations. Field observations have shown that albino redwoods growing in the natural range which exhibits fewer signs of cyclical dieback are most likely to be found growing in isolated interior groves. These trees are far more likely to be subject to weather extremes than their coastal brothers. These redwoods exhibit better stomatal control than trees near the coast & may be better adapted to coping with rapidly changing weather environments. In the broader sense, these implications may have a larger impact on the redwoods species as scientists delve into the questions of climate change. The answer may not lie with redwoods just adapting to new climates, but one that offers adequate moisture and a minimal shift in daily temperature & humidly variations. Redwood trees that can withstand large temperature and humidity shifts may be better suited to planting in new environments.
The Amador Sentinel growing high above the banks of the Mokelumne River & Highway 49 is a normal green coast redwood located in the Sierra foothills. The tree is situated on a dry south-facing slope surrounded by grasslands. How this tree survives hot scorching summers may be in its ability to conserve water through strong stomatal control and adaptation to an environment that favors lower variation in temperature & humidity.
Can you spot the redwoods growing in this picture? Believe it or not, these coast redwoods are thriving amongst Ponderosa, Gray, & Knob Cone Pines which are species specifically adapted to drier environments. The trees are growing in an isolated interior grove within Pope Valley in Napa County. These redwoods endure colder winters, hotter summers, and drier conditions compared to trees near the coast. What’s remarkable is these redwoods have adapted to survive in this difficult environment.
In conclusion, the foliage in albino redwoods has shown remarkable resiliency to survive the harsh weather extremes of the Sierra Nevada Mountains. The results were quite astonishing for a mutation that once was considered quite fragile. This study demonstrated that albino redwood foliage does have adequate stomata control within a certain temperature & humidity band. It also shows that albino foliage does have the ability to adapt to weather extremes so long as the changes are gradual. Looking at the species as a whole, the key to redwood endurance may not hinge on a gradually warming climate, but an environment that lends itself to where trees can readily adjust to rapidly changing weather conditions. Whether the climate is hot or cold, it appears an environment that offers a lower variation of temperature & humidity may favor long-term survival for coast redwoods. The implications of these results may lend to normal green redwoods being genetically selected for more efficient water conservation qualities. This in turn could lead to trees that are better adapted to shifting weather patterns and drier conditions as the species faces the challenges of climate change. Individuals that exhibit robust stomatal control may be key in preserving the species into the new millennium.