Function

	Secure the plant (and its surrounding soil)
	Uptake of nutrients Only at the root tips and hairs – active and passive mechanisms Roots grow and encounter nutrients Mass flow of water to roots (transpiration stream) Nutrient concentrations will stimulate branching (more root tips and increased nutrient uptake)
	Uptake of water
	Mechanism for carbon entry to soil
	Improve water infiltration characteristics – promotes porosity
	Tap roots – (dicots only) – function is for plant stability and to access deep nutrients and water
	Fiborous roots (esp grasses) – prolific at the surface. In temperate pastures the average rooting depth can be as little as 3 cm with high fertilizer use – more typically 10 cm.
	Buried stolons and rhizomes – vegetative reproduction only

Some key points

	Root mass under pasture can be greater than in any other plant system – many grasslands have 20 T/ha of root material
	Typically 50% of plant growth occurs underground (30-85%) – phalaris pastures in Australia can have a root:shoot ratio = 5
	Many of these roots are dead We can’t easily separate live from dead roots. What is a dead root? – a) many roots have low metabolic activity and function simply as water channels, b) in times of desperation grasses can revive dead roots

  Stress Effects - Fertility

	Low fertility promotes increased root mass – root elongation rather than branching to maximize the volume of soil
	Low fertility results in finer roots –surface area will increase by the square of the reduction in diameter
	Fertilizers are surface applied and promotes shallower rooting
	Low fertility of rangelands – they have higher root mass

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  Stress Effects - Grazing

	Defoliation results in slowed root activity (ultimately death) below-ground
	Good grazing management is associated with other good practice (fertilizer use) and typically results in greater overall plant growth i.e. more roots
	excessive grazing will deplete a stand and decrease root mass

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  Stress Effects - Water stress

	Generally decrease root growth but increases root:shoot ratio
	Rangelands tend to be drier – which contribute to their higher root mass.

Stress Effects - Waterlogging

	Roots obtain their oxygen from the soil (not from any internal circulating system) and are very sensitive to water logging.
	Much waterlogging is local (surface flooding) and roots lower in the soil might not be flooded and can survive

  Stress Effects - Root pests

	Fungi (root and collar rot), nematodes, grubs/larvae
	Earthworms don’t eat living roots
	Not all root consumption is necessarily bad – as livestock eat leaves with often positive effects, some root removal is tolerable

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