dynamic mineral accumulation

MICHAEL S . H I LL

DYNAMIC MINERAL ACCUMULATION—FACT OR FICTION?

1

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.

2

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.

4

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

8

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.

17

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:

19

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

20

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.”

21

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.

22

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

• …

23

…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