new root presentation
DESCRIPTION
I shared this presentation with my Soil Fertility class at Western Illinois University in August 2012TRANSCRIPT
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?