Lecture 5: Roots and its modification

Buttress or tabular roots

Vertically flattened roots that projects out of the ground and lower trunk at the base of large trees

Can be found in many rainforest trees

Stilt and Prop roots

Branched/ Adventitious roots arise from the lower parts of the trunk or branches

Provides support to the stem are branches

Common characteristics of mangrove trees

Pneumatophores

Aerial breathing roots

Commonly found in magroves

Aerial roots

Found in epiphytes such as orchids

Contractile roots

In order to maintain a corm or bulb under the soil, these roots slowly pull the bulbs/ corms inwards

Mycorrhizae (Fungi)

Forms symbiotic relationship with soil fungi (Mycorrhizae) to better absorb essential minerals

Nodules

Are found in Legume Family (now called Fabaceae)

Association with nitrogen fixing bacteria

Supports the tree weight in shallow soils of rainforest

Increases the surface area over which nutrients can be absorbed from the soil

Most rainforest soil is very poor in nutrients due to leaching and run off. All nutrients are largely found at the surface level

Rhizophora

Spongy outgrowths from the roots below

Function as breathing roots

In swampy or tidal envt., where the soil is usually flooded or water- logged, roots often grow upwards until they are above high- tide level.

Even though roots live in soil, they still require oxygen for aerobic respiration. flooded soil = depleted of O2

To avoid suffocation, pneumatophores contain as much as 80% aerenchyma (Functions like a snorkel, O2 diffuses to submerged roots

Aides in absorption of water from rain

Enables plant to climb and anchor to any surfaces it is growing on

Orchids produce chlorophyll in aerial root to manufacture food

Some parasitic epiphytes such as the mistletoe have roots that penetrates the host plant tissues and absorb nutrients

Contractile roots will Shrivel and hence shrink in length

Fungus are able to absorb and concentrate phosphorus much better than root hairs

Can also improve water absorption and uptake of certain minerals from the soil

Form symbiotic relationships with nitrogen-fixing bacteria (rhizobial bacteria) and fungi that lives in tumor- like root nodules.

Nitrogen fixing bacteria able to convert atmosphere N2 gas to ammonia to amino acids.

A very special way to deliver nutrients to the shoot (Plants like N2)

Food/ water storage

Roots are enlarged and store large quantities of starch and other carbohydrates which may be later used for extensive growth