The hidden half of agriculture
How many of you regularly look at crop roots ?
John McGillicuddy
Bill Darrington (Persia, IA)
All you need to do 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 !
Seminal roots cease new growth shortly after the coleoptile emerges from the soil surface. The nodal root system becomes visible at ~ V1. The nodal root system
becomes the dominant system by V6.
4 weeks8 weeks16 weeks
7 feet deep !!
1926
?
Brady and Weil (2002)Brady and Weil (2002)
PLOW PAN
Compacted layers can severely limit root growth
Sub-soil water and nutrients
Adapted from Hunt et al. (1986)
Long term no-till(w/ healthy soil biology) Intensive tillage
Ontario Ministry of Ag and Food
Plow panNetwork
of biopores
Which solution would you use ?
WIU Allison Organic Research Farm – September 2007
January
Please plant me no-till next spring !!
Visual evidence of biodrilling
Rapeseed root
Canola root
The experiment was planted to corn on May 29 2008
Corn following radish established well and had the lowest weed
pressure in the row.
Maybe you should come out to the farm and see how things
look this fall…
Aluminum toxicity
Aluminum toxicity
Chemical toxicities can inhibit root growth
http://www.agnr.umd.edu/users/nrsl/entm/nematology/images/eis143.jpg
Galled root system of tomato infected with root-knot nematode, Meloidogyne sp., compared with non-
infected root system
Root knot juvenile penetrating a tomato rootRoot pathogens can inhibit root growth
You won’t know what is happening underground unless you take a look…
Roots have many functions !
Absorptive network for limiting soil resources of water and nutrients
Mechanical structures that support plants, strengthen soil, construct channels, break rocks, etc. Hydraulic conduits that redistribute soil water and nutrients Habitats for mycorrhizal fungi, rhizosphere and rhizoplane organisms
Carbon pumps that feed soil organisms and contribute to soil organic matter
Storage organs
Chemical factories that may change soil pH, poison competitors, filter out toxins,
concentrate rare elements, etc.
A sensor network that helps regulate plant growth
http://www.sparknotes.com/biology/plants/plantstructures/section2.rhtml
http://www.sparknotes.com/biology/plants/plantstructures/section2.rhtml
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.
The cell wall of the endodermis (pink inner strip of cells) is waterproofed by the suberised Casparian strip, which forces water to enter the symplast before it can enter the root xylem
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/35.03.jpg
Water moves upward through plants whenever there is a progressively morenegative gradient of water potential along the soil-plant-atmosphere continuum
H20
H20
H20H20
A continuous chain of water molecules is
pulled up through the
plant
Solar energy drives the process
Plants provide the conduit
Understanding nutrient uptake
Transpirationalstream
H20
H20
Root exudatesactivate soil microbes R
oo
t gro
wth
N, S, P
Diffusion
Nutrient uptake is an active and selective process
Rhizosphere
Zone of root influence
The rhizophere is normally < 10 % of soil volume
Roots normally occupy < 1% of topsoil volume
Navigating the rhizosphere
RhizoplaneEndo-
Rhizosphere Ecto-Rhizosphere
End of the rhizosphere
(Lavelle and Spain, 2001)
< 10% of soil volume
> 90% of soil
volume
Mic
rob
ial
acti
vity
A few millimeters
Acute root
disease
Feed the soil vs. Feed the crop Both strategies are important !
Healthy roots need available nutrients !Unhealthy roots use nutrients inefficiently…
Chronic root malfunction
Healthy cowpea nodule with a pink
interior
Ectomycorrhizae
Arbutoid mycorrhizae
Ericoid endomycorrhizae
Orchid endomycorrhizae
AM endomycorrhizae
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
Ectomycorrhizal roots
Close up of ecto-mycorrhiza
Increase nutrient (P) uptake suppress pathogens
Mediate plant competition Improve soil structure
GlomalinSuperglue of the soil ??
Roots are worth
a closer look !
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