New root presentation

The hidden half of agriculture

ROOTS

Reading for the week

Reading Questions

1) Why have roots been studied so much less than the above-ground

components of plants?

2) What was the “Green Revolution” and why does Dr. Lynch think ”roots are

the key to a second green revolution”?

3) How did crop breeders accomplish most of the yield gains achieved during

the 20th century and how does Dr. Lynch think they should shift their focus?

4) The article discusses 4 promising strategies for root research under the

headings “Designer roots”, “Stealth scavengers”, “Microbial manipulations”

and “A healthy fixation”. For each of the 4 research strategies, describe (in

your own words), something that you thought was particularly interesting.

5) If you had an opportunity to be involved with innovative root research (e.g.,

as an intern at a lab or a farmer trying a new technology), briefly describe

what you would like to try.

Submit your answers to the these questions using WO before the start of

class on Friday 8/31.

Have you ever taken the time

to look closely at crop roots?

Healthy

shoot growth

and high

yields

white color

proliferate

in all

directions

extensive

growth into

the sub-soil

minimal

evidence of

deformities

Efficient

use of soil

resources

What should you look for?

Bill Darrington (Persia, IA)

Ray Rawson

Francis Childs

VF = Management system for optimum

root extension and function

Getting dirty with 2 champions of Vertical Farming

Ken Ferrie inspecting

corn roots on a farm in

central IL.

"One of our primary goals is to get the

first three sets of crown roots deep into

the soil… In vertical-tillage, no-till or strip-till

conditions, the first set of crown roots will go

down. But, when we do horizontal tillage

before planting, except in a few conditions

like sand, no matter what we did in the fall,

the first two sets of crown roots almost

always turn on the dense layer. Hopefully,

with fall vertical tillage, the third set will

penetrate.“

Ken Ferrie – Farm Journal, September 2006

You really won’t know what is happening

underground unless you take a look…

All you need is

a shop-vac and

a hose :-> !

Its just like going to the dentist!

http://www.agry.purdue.edu/ext/corn/news/timeless/Roots.html

The nodal root system becomes visible at ~ V1.

The nodal root system becomes the dominant

system by V6.

Understanding corn root

development

The seed roots stop

growing shortly after

the coleoptile

emerges from the

soil surface.

Have you ever heard of “floppy corn”

or “rootless corn” syndrome?

Where are the nodal roots?

“Floppy corn” or “rootless corn” occurs when surface soil is too

dry for healthy elongation of roots from the first node (V2 to V4).

Young roots emerging from the first node will die if the

meristematic tissue desiccates prior to extension into moist soil.

The crown of a young corn plant is typically located only 3/4

inch or so below the soil surface and so is particularly

vulnerable to dry upper soil conditions.

1926

http://www.soilandhealth.org/01aglibrary/010139fieldcroproots/010139toc.html

4 weeks

8 weeks

16 weeks

7 feet deep !!

Corn root development documented in the 1920s

If this was possible 90

years ago, just think

what is possible

today?

Crops grown on modern row

spacings generally do not grow

such wide root systems

Wading pool gardens

in my back yard

How is it possible for healthy crops to

grow with such a limited rooting volume?

Watermelon roots that

grew in a wading pool

Wading pools do NOT provide an optimal rooting zone

but a small root system can support healthy shoot

growth with adequate moisture and nutrition.

?

All you need to do to grow healthy corn roots

is use rootworm resistant genetics… right??

When rootworm pressure is high, rootworm resistant

genetics normally result in much healthier roots

Severe damage by corn

rootworm larvae to roots of

a biotech corn rootworm

hybrid

http://www.ipm.iastate.edu/ipm/icm/2006/11-13/btcorn.html

Rootworm resistant genetics are not a silver bullet !

A significant correlation was found between the number

of years Cry3Bb1 corn had been grown in a field and

survival of western corn rootworms. Interviews with

farmers indicated Cry3Bb1 corn had been grown for at

least three consecutive years in all of the fields

containing resistant corn borers.

The researchers concluded insufficient planting of

refuges and non-recessive inheritance of resistance is

likely to have contributed to the development of

resistance.

They noted a 2009 study done by the Center for Science

in the Public Interest indicated only 50% of Bt maize

planted in Midwest complied with EPA requirements for

refuge size and proximity to Bt fields.

http://cornandsoybeandigest.com/blog/bt-resistant-corn-borers-spur-concerns

“Most important, though, for effective corn rootworm

management is to consider a long-term, integrated approach

that includes multiple tactics, such as adult suppression

programs, use of soil insecticides at planting, rotation of Bt

hybrids that express different Cry proteins, and rotation to

nonhost crops.

Many producers have relied on a single tactic for too many

years, and unfortunate consequences are beginning to emerge.

As harvest gets under way this fall, I suspect that more

producers in northwestern Illinois will encounter lodged corn

that has been severely damaged by western corn rootworms.

As I learn more about this evolving situation, I will keep you

informed”.

Mike Gray – U of I Extension Entomologist - 2011

8/17/2012

Diabrotica virgifera Diabrotica barberi

Western corn rootworm beetle Northern corn rootworm beetle

What do you know about corn rootworm biology ??

http://plantandsoil.unl.edu/croptechnology2005/plant_phys/?what=animationList

http://plantandsoil.unl.edu/croptechnology2005/plant_phys/?what=animationList

http://plantandsoil.unl.edu/croptechnology2005/plant_phys/?what=animationList

http://plantandsoil.unl.edu/croptechnology2005/plant_phys/?what=animationList

Goose

necking

http://plantandsoil.unl.edu/croptechnology2005/plant_phys/?what=animationList

http://plantandsoil.unl.edu/croptechnology2005/plant_phys/?what=animationList

http://plantandsoil.unl.edu/croptechnology2005/plant_phys/?what=animationList

European entomologists are studying natural predators of corn

rootworms (collected from soils in N. and S. America) for use in

controlling corn rootworms in Europe (where rootworms are not native)

In North and South America, corn rootworms are attacked by

many pathogens, predators and parasitoids, some of which

are specialized natural enemies of corn rootworms.

Studies have shown that

many of the natural enemies

of CRW are more common in

reduced-tillage systems, and

in fields with higher levels of

organic matter.

Journal of Economic Entomology

Article: pp. 330-339 | Abstract | PDF (1.44M)

Disruption of Host Location of Western Corn Rootworm Larvae with

Carbon Dioxide

E. J. Bernklau, E. A. Fromm, and L. B. Bjostad

Department of Bioagricultural Sciences and Pest Management, Colorado

State University, Fort Collins, CO 80523

Elevated concentrations of carbon dioxide (CO2) prevented western corn

rootworms from locating the roots of growing corn in behavioral bioassays

conducted in soil tubs. When CO2 was pumped into one end of a soil tub,

significantly more larvae were recovered from soil at the treated end than

from soil around a growing corn plant at the opposite end of the tub. In

controls with ambient air pumped into one end of a soil tub, significantly

more larvae were recovered from the soil around the corn plant than from

soil on the treated side. Larvae were unable to locate the roots of corn

seedlings when CO2-generating materials were mixed into the soil.

When damaged by corn rootworms, the roots of

some corn plants release a chemical called (E)-β-

caryophyllene that recruits an entomopathogenic

nematode (Heterorhabditis megidis) to feed on

corn rootworms.

Modern corn breeding has resulted in loss of the (E)-β-

caryophyllene signal in many hybrids, reducing their ability to

recruit H. megidis.

Under field conditions, the infection rate of corn rootworms with

H. megidis were found to be 5x higher on a corn variety

producing the below-ground signal than on a variety that does

not. Moreover, spiking the root system of a non-producing variety

with synthetic (E)-β-caryophyllene decreased the emergence of

corn rootworm adults

by > 50%.

The root promoting effects of soil

biology are underappreciated

Dramatic effect of steam

sterilization and compost on

growth of pepper plants

competition parasitism

antibiosis induced resistance

Don’t forget that soil biology can both

promote and inhibit crop root growth

and function

Acute

root

disease

Chronic root

malfunction

VS.

This unfortunately

is the norm in

agriculture

Chemical, physical and biological

factors can cause CRM!

Aluminum

toxicity

Aluminum

toxicity

Chemical toxicities can

inhibit root growth & function

Al toxicity is very common in

the SE US and in tropical

countries like Brazil Brady and Weil

Understanding aluminum toxicity

Toxic forms

of Al are

bioavailable

at pHs < 5.5

Aluminum toxicity

is minimal above

a water pH of 5.5

http://www2.ctahr.hawaii.edu/tpss/research_extension/rxsoil/alroot.gif

Fe and Mn toxicities also

occur at lower pHs

What damaged these corn roots?

Boron was included

in starter fertilizer

http://www.sdstate.edu/ps/soil-lab/loader.cfm?csModule=security/getfile&PageID=788496

On-line tool for estimating

maximum rates of in-row fertilizer

Damage is most likely in dry

coarse textured soils

N and P promote root branching and proliferation

http://w

ww

.naic

c.o

rg/m

eeting/2

011/In%

20R

educed%

20T

illage%

20

-Vocasek.p

df

Air pruning promotes root branching

Soil block system for growing transplants

Air pruning promotes root branching

Ontario Ministry of Ag and Food

Why do crops on tiled-drained land

tend to be more drought resistant ?

Ontario Ministry of Ag and Food

Do crop roots grow toward water?

Roots elongate directed by gravity in aerobic soil!

Soil can

get too

hot for

optimal

root

growth!

Soil aeration affects soil temperature

which strongly affects rate of root growth

http://www.naicc.org/meeting/2011/In%20Reduced%20Tillage%20-Vocasek.pdf

Brady and Weil (2002)

Brady and Weil (2002)

Sub-soil water

and nutrients

Compaction strongly impacts root growth and function

What causes sidewall

compaction?

Waiting for drier soil

is the most important solution

Adapted from Hunt et al. (1986)

Tillage systems

affect root

growth and

function

Long term no-till (w/ healthy soil biology) Intensive tillage

Ontario Ministry of Ag and Food

Plow pan

Network

of cracks

and

biopores

Annual

ryegrass

roots

penetrating 40”

Radish

roots

> 40”

after 1.5

months

Visual evidence of biodrilling

(Williams and Weil, 2004)

Another type

of biodrill

Which approach

would you use ?

Weil

Roots perform

many valuable

functions !

Why are healthy roots so

important?

Carbon pumps that feed soil organisms and

contribute to soil organic matter

Energy and nutrient storage organs

Chemical factories that change soil pH,

poison competitors, filter out toxins,

concentrate rare elements, etc.

A sensor network that helps regulate plant

growth

In addition to the most obvious functions

physical support and uptake of water and nutrients

ROOTS are:

Macro-

anatomy of roots What’s

missing

if this

was a

corn

plant?

http://www.sparknotes.com/biology/plants/plantstructures/section2.rhtml

Micro-anatomy of roots

What is the function

of the root cap?

Physical protection

source of lubrication,

& sensor of gravity

What is the function of root hairs?

• Increased surface area for

uptake of water and nutrients

• Anchoring of roots allowing

root extension

The cell wall of the endodermis (pink inner strip of cells) is waterproofed by the

Casparian strip, which forces water to enter the symplast before it can enter the

root xylem

cortex

epidermis endodermis

root hair

phloem

xylem

The movement of fluids from the root hairs to the xylem

can occur through one of two conductive pathways– the

apoplast and the symplast.

The apoplast route consists of inter-cellular spaces

within the root cortex along which water and solutes can

diffuse.

The symplast route consists of channels through cells

along which water and solutes are actively transported.

Apoplast vs. symplast

http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/35.03.jpg

Nutrient uptake can be an active or a passive process

insid

e c

ell

ou

tsid

e c

ell

Plants are highly selective for potassium!!

Outside cell

Inside cell

K+

H+

NO3-

H+

The pH of a plant’s

rhizosphere changes as

the plant regulates its

internal charge balance.

http://departments.agri.huji.ac.il/plantscience/topics_irrigation/uzifert/4thmeet.htm

Which plant received nitrate (NO3-)?

Which plant received ammonium (NH4+)?

The ins and outs of plant nutrition

Transpirational

stream

H20

H20

Root exudates

activate soil microbes Ro

ot g

row

th

N, S, P

Diffusion

Microorganisms produce

most but not all of the

enzymes need to digest OM

Plants take up mostly inorganic forms of nutrients

when inorganic forms of nutrients are readily available

In some natural ecosystems (e.g., tundra), organic

forms of nutrients are very important

Water moves upward

through plants

whenever there is a

negative gradient of

water potential along

the soil-plant-

atmosphere

continuum

Why does

water move

up into

plants?

H20

H20

H20 H20

A continuous

chain of water

molecules is

pulled up

through the

plant

Solar energy

drives the

process

Plants provide

the conduit

Rhizosphere

Zone of root

influence

The rhizosphere is

normally << 10 % of

topsoil volume

Roots normally

occupy < 1% of topsoil

volume

Navigating the rhizosphere

Rhizoplane

Endo-

Rhizosphere Ecto-Rhizosphere

End of the

rhizosphere

(Lavelle and Spain, 2001)

< 10% of soil

volume

> 90%

of soil

volume

Mic

rob

ial acti

vit

y

A few millimeters

Healthy

cowpea

nodule

with a

pink

interior

Legume

nodules

come in

many shapes

and sizes

Legume

love

affair

Sarrantonio

Lots of complicated biochemistry – very intensively studied!!

Examples of rhizobia innoculant

Subterranean clover*

White clover

Cowpea Group

(Bradyrhizobium japonicum spp.)

Alyceclover

Cowpea

Kudzu

Peanut

Lespedeza

Joint vetch

Lupine Group

(Rhizobium lupini)

Blue lupine

White lupine

Pea and Vetch Group

(Rhizobium leguminosarum)

Bigflower vetch

Common vetch

Hairy vetch

Roughpea

Winter pea

Other**

Bird’s-foot trefoil (Rhizobium loti)

Cicer milk vetch

Crown vetch

Sainfoin (Rhizobium)

Soybean (Rhizobium japonicum)

Kura clover

Leucaena

Soybean has its own inoculation group!!

Inoculation groups for commonly grown legumes

How much N do soybeans fix and how much

of this N is left behind after harvest?

A good soybean crop will fix >150 lbs of N/ac but

>200 lbs of N may be removed in the harvested beans.

N

-N

Mycorrhizae - internet of the soil

Ectomycorrhizae

Arbutoid

mycorrhizae

Ericoid

endomycorrhizae

Orchid endomycorrhizae

AM endomycorrhizae

2 main types of mycorrhizal associations

Lavelle and Spain (2001)

•Many plants are

connected

underground by

mycorrhizal hyphal

interconnections.

•Mycorrhizal (AM)

fungi are not host

specific.

Illustration by Mark Brundrett

Mycorrhizal Networks: Connecting

plants intra- and interspecifically

Increase nutrient (P) uptake suppress pathogens

Mediate plant competition Improve soil structure

Glomalin

Superglue

of the soil ??

There are many

mycorrhizal

inoculants on the

market and growing

evidence that they

can increase crop

performance but it is

important to keep in

mind that they are a

much less proven

technology than

legume inoculants

Some of the most dramatic responses to

mycorrhizal inoculation occur during

reforestation projects

Have you ever wondered how far out tree roots extend?

?

Tree roots often extend >2 times farther than the canopy

?

Is this tree likely to remain healthy?