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 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

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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 pan Network 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 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 Chemical toxicities can inhibit root growth

Galled root system of tomato infected with root-knot nematode, Meloidogyne sp., compared with non- infected root system Root knot juvenile penetrating a tomato root Root 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

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

Water moves upward through plants whenever there is a progressively more negative gradient of water potential along the soil-plant- atmosphere continuum

H20H20 H20H20 H20H20 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 Transpirational stream H20H20 H20H20 Root exudates activate soil microbes Root growth 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 Rhizoplane Endo- Rhizosphere Ecto-Rhizosphere End of the rhizosphere (Lavelle and Spain, 2001) < 10% of soil volume > 90% of soil volume Microbial activity 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) uptakesuppress pathogens Mediate plant competition Improve soil structure Glomalin Superglue of the soil ??

Roots are worth a closer look !