dynamic mineral accumulation
TRANSCRIPT
MICHAEL S . H I LL
DYNAMIC MINERAL ACCUMULATION—FACT OR FICTION?
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TOPIC OF STUDY
• Dynamic accumulators are “plants that amass a greater
than usual amount of a particular nutrient in their
foliage.”
• For years, many writers of popular
gardening/permaculture/forest gardening books have
advocated for the use of dynamic accumulators to aid
in sustainable nutrient cycling.
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AN EXAMPLE OF ONE OF THE LISTS
Dynamic accumulators for temperate homegardens(Adapted from Jacke and Toensmeier, 2005.)
Botanical Name Common Name Nutrients Accumulated
Acer saccharumBetula lentaCarya ovataChamaemelum nobileCornus floridaJuglans nigraNasturtium officinaleRobinia pseudoacaciaRumex spp.Stellaria mediaSymphytum spp.Taraxacum officinaleUrtica dioica
sugar mapleblack birchshagbark hickoryGerman chamomileflowering dogwoodblack walnutwatercressblack locustsorrels and dockschickweedcomfreysdandelionnettles
Ca, KCa, K, PCa, K, PCa, K, PCa, K, PCa, K, PCa, K, P, Mg, Fe, Na, SCa, K, N2
Ca, K, P, Fe, NaK, PCa, K, P, Fe, Mg, SiCa, K, P, Cu, Fe, Mg, SiCa, K, S, Cu, Fe, Na 3
TOO GOOD TO BE TRUE?
• The reasoning went that if one planted these
species near other key species (e.g., fruit or nut
trees), then the key species would eventually gain
access to these nutrients taken up by the
accumulators and deposited back onto the soil
with litter fall.
• Recent questioning by many, some of them authors
of the very books which promulgated the notion of
dynamic mineral accumulation, if preferential
dynamic mineral accumulation is a fact.
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FICTION?
• Dave Jacke: “I have heard through the grapevine that Robert Kourik is sorry to have propagated the idea of dynamic accumulators. (As far as I know, he coined the term.) There is not very good research to back up that particular idea, and I agree with him. I even think that my own attempts to back it up
are not close enough to the mark to feel solid about it. I do fervently hope the idea is true, and it makes sense, but I consider it unproven at this point.”
• John Kitsteiner: “We will start with the scientific evidence … Unfortunately, there is not much. In fact, I can find almost no research into dynamic accumulators. Strike that, I can find NO research into this concept al all. None … As it turns out, it appears that the concept of dynamic accumulators has been passed down and around for so long that is has been accepted as fact.”
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HOWEVER …
• “Through their deep-reaching roots, [cover crops] help to break up hardpan and bring minerals to the surface for other plants to utilize.”
• Legumes, cereal grains, brassicas
• Practitioners continue to subscribe to the idea of preferential dynamic mineral accumulation.
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GARDENER-SCIENTIST
My “forest garden”
100+ species in 1500 sq. ft.
Fruit and nut treesFruit and nut shrubs
Perennial herbs
Ground coversDynamic accumulators 7
…A MILLION HILLS GREEN WITHCROP-YIELDING TREES…
• Multistrata
homegardening in
temperate climates:
• A sixth temperate AF
system?
• Movement towards
local food, growing
interest in
homegardens
• Edible landscaping
SymphytumAchillea
Stellaria
Malus
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FACT OR FICTION:WHAT DOES THE SCIENCE SAY?
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• There is research which shows that some plants preferentially take up certain essential nutrients, in concentrations well above those of other plants grown under the same conditions.• Perhaps not as “clean” as we’d like this to be.
• Note: Though I consulted some of the literature concerning hyperaccumulation of toxic metals in roots and shoots of some plants, I will not discuss these here.• Phytoremediation
• Phytomining
BROADLY ET AL. (2004)JOURNAL OF EXPERIMENTAL BOTANY
• 144 herbaceous angiosperms grown
hydroponically and fertilized with prepared
nutrient solutions.
• Significant variation found between angiosperm
orders: Ca, K, Mg
• No significant variation found between
angiosperm orders: N, P
• Significant variation in shoot mineral
concentration observed at the species level.
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BROADLY ET AL. (2004)JOURNAL OF EXPERIMENTAL BOTANY
Mineral Nutrient
Highest SpeciesConcentration
(% of dry weight)
Mean (% o.d.w.)(117 species)
Organic NLycopersicon esculentum (6.7%)Helianthus annuus (6.4%)
6.04
PFreesia elimensis (1.47%)Echinofossulocactus spp. (1.42%)
0.79
KBorago officinalis (9.2%)Mesembryanthemum criniflorum(9.0%)
4.94
CaBrassica oleracea (4.4%)Hypoestes sanguinolentua (3.6%)
1.22
MgAmaranthus hypochondriacus (0.95%)Echinofossulocactus spp. (0.92%)
0.36
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SHTANGEEVA ET AL. (2009)PLANT AND SOIL
• Greenhouse trials with plants collected in
Northwest Russia.
• Found that nutrient concentrations varied
significantly by species.
• “Plants reflect not only soil nutrient availability, but
the uptake process is mainly dependent upon the
genetic capability of particular plant species for
maintaining a certain level of element
concentrations in different plant parts.”
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SHTANGEEVA ET AL. (2009)PLANT AND SOIL
Mean Concentration in Leaves, %Plant K Na CaPlaintainCouch-grassWheatOatsBarleyRye
3.713.386.686.686.825.54
0.060.060.060.390.550.13
1.860.470.860.410.470.78
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THOMPSON ET AL. (1997)NEW PHYTOLOGIST
• Regional field study of 83 plants in Central England.
• Shoot P and organic-N concentrations:• Species-level trait
• Shoot Ca and Mg concentrations:• Influenced by ancient
evolutionary processes
• At or above the level of order
• Shoot K concentration:• Intermediary
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“CLASSIC” ACCUMULATORS
Botanical Name Common Name Nutrients Purportedly
Accumulated**
Urtica dioica
Stellaria media
Symphytum spp.
Stinging nettles
Chickweed
Comfrey
Ca, K, S, Cu, Fe, Na
K, P
Ca, K, P, Fe, Mg, Si
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**Jacke and Toensmeier, 2005
HERBACEOUS ACCUMULATORS
N P K Ca Mg
2.78 0.27 2.81 1.28 0.34
Urtica dioica (nettles)
4.26 0.51 2.61 3.87 0.67
Stellaria media (chickweed)
4.17 0.59 6.59* 1.20 0.73
Symphytum spp. (comfrey)**
3.53 0.50 5.86 1.44 0.30
*Highest of 83 species sampled
**Data not from the Thompson field study
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• “…species with relatively nutrient rich (or poor)
leaves on one substrate also tend to be nutrient rich
(or poor) on all other substrates, irrespective of soil
pH, altitude, and land use.”
• Plants do not simply have higher mineral nutrient
accumulations because they grow only in soils with
already higher levels of those nutrients.
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THOMPSON ET AL. (1997)NEW PHYTOLOGIST
• Looking only at species taken from soils with pH
6.00-6.99:
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THOMPSON ET AL. (1997)NEW PHYTOLOGIST
y = 0.2594x - 0.0789
R² = 0.0047
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
6.0 6.2 6.4 6.6 6.8 7.0
Ca
(%
of d
ry w
eig
ht)
pH
• Looking only at species taken from soils with pH
6.00-6.99:
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THOMPSON ET AL. (1997)NEW PHYTOLOGIST
n Mean Std.
dev.
Median Min Max Q1 Q3
45 1.60 0.92 1.5 0.3 3.9 0.8 2.3
FOULDS (1993)NEW PHYTOLOGIST
• 368 plant species collection from 36 habitats in
Australia
• “Much evidence that large differences in nutrient
concentrations occur between species.”
• Some nutrient-rich plant families:
• Solanaceae, Chenopodia
• Families generally rich in N, P, K:
• Primalaceae, Asters, Brassicas
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HOLZMUELLER ET AL. (2007)PLANT AND SOIL
• “High concentrations of
these cations [Ca, K, Mg) in
C. florida foliage suggest
that this species may play
an important role in nutrient
cycling by acting as a
“pump” that draws cations
from deeper in a soil profile
and cycles them through
the forest floor and surface
soil.”
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SUMMARY
• With respect to mineral accumulation,
species differentiation has been established
as a fact.
• Nair (1993): “Some tree and shrub species can
selectively accumulate certain nutrients, even in
soils which contain very small amounts of these
nutrients.”
• My survey of the literature shows that the
same can be said for herbaceous species.
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QUESTIONS/RESEARCH TOPICS
• What native species (to North America) can be used as dynamic accumulators?• What mineral nutrients do these take up preferentially?
• Biodiversity considerations
• How to employ dynamic accumulators in the five AF practices of N.A.?• Forest farming
• Silvopasture
• Windbreaks/shelterbelts
• Riparian/upland buffers
• Alley cropping
• Interspecies interactions and competition
• Economics
• …
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…A MILLION HILLS GREEN WITHCROP-YIELDING TREES…
• Multistrata
homegardening in
temperate climates:
• A sixth temperate AF
system?
• Movement towards
local food, growing
interest in
homegardens
• Edible landscaping
SymphytumAchillea
Stellaria
Malus
24