Dr. Archana Singh

1

SET- UPS

1. SOIL PROFILE

“Soil profile is defined as the vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock.”

Soil Profile

The soil is the topmost layer of the earth’s crust mainly composed of organic minerals and rock particles that support life. A soil profile is a vertical cross-section of the soil, made of layers running parallel to the surface. These layers are known as soil horizons.

The soil is arranged in layers or horizons during its formation. These layers or horizons are known as the soil profile. It is the vertical section of the soil that is exposed by a soil pit. The layers of soil can easily be identified by the soil colour and size of soil particles. The different layers of soil are:

Topsoil

Subsoil

Parent rock

Each layer of soil has distinct characteristics.

Soil profile helps in determining the role of the soil as well. It helps one to differentiate the given sample of soil from other soil samples based on factors like its colour, texture, structure, and thickness, as well as its chemical composition.

Dr. Archana Singh

2

Layers of Soil

The soil profile is composed of a series of horizons or layers of soil stacked one on top of the other. These layers or horizons are represented by letters O, A, E, C, B and R.

The O-Horizon

The O horizon is the upper layer of the topsoil which is mainly composed of organic materials such as dried leaves, grasses, dead leaves, small rocks, twigs, surface organisms, fallen trees, and other decomposed organic matter. It contains about 20 to 30% of organic matter. This horizon of soil is often black brown or dark brown in colour and this is mainly because of the presence of organic content.

The A-Horizon or Topsoil

This layer is rich in organic material and is known as the humus layer. This layer consists of both organic matter and other decomposed materials. The topsoil is soft and porous to hold enough air and water.

In this layer, the seed germination takes place and new roots are produced which grows into a new plant. This layer

consists of microorganisms such as earthworms, fungi, bacteria, etc.

The E-Horizon

This layer is composed of nutrients leached from the O and A horizons. This layer is more common in forested areas and has lower clay content.

The B-Horizon or Subsoil

It is the subsurface horizon, present just below the topsoil and above the bedrock. It is comparatively harder and compact than topsoil. It contains less humus, soluble minerals, and organic matter. It is a site of deposition of certain minerals and metal salts such as iron oxide.

This layer holds enough water than the topsoil and is lighter brown due to the presence of clay soil. The soil of horizon-A and horizon-B is often mixed while ploughing the fields.

The C-Horizon or Saprolite

This layer is devoid of any organic matter and is made up of broken bedrock. This layer is also known as saprolite. The geological material present in this zone is cemented.

The R-Horizon

It is a compacted and cemented layer. Different types of rocks such as granite, basalt and limestone are found here.

Expected Questions based on Soil Profile

• What does this set-up demonstrate? Define it.

• Name the different horizons from top to bottom.

• Write briefly about the zone of illuviation.

• Which horizon is called the zone of leaching and why?

• What is humus? Which layer consists of maximum humus?

• Which layer is highly fertile and why ?

Dr. Archana Singh

3

2. RAUNKIAER’S LIFE FORM

The Raunkiær system is a system for categorizing plants using life-form categories, devised by Danish botanist Christen C. Raunkiær and later extended by various authors.

Life forms

Dr. Archana Singh

4

History It was first proposed in a talk to the Danish Botanical Society in 1904 as can be inferred from the printed discussion of

that talk, but not the talk itself, nor its title. The journal, Botanisk Tidsskrift, published brief comments on the talk by M.P. Porsild, with replies by Raunkiær. A fuller account appeared in French the following year.[1] Raunkiær elaborated further on the system and published this in Danish in 1907.[2][3]

The original note and the 1907 paper were much later translated to English and published with Raunkiær's collected works.[4][3][5]

Modernization Raunkiær's life-form scheme has subsequently been revised and modified by various authors,[6][7][8]but the main structure has survived. Raunkiær's life-form system may be useful in researching the transformations of biotas and the genesis of some groups of phytophagous animals.[9]

Subdivisions The subdivisions of the Raunkiær system are premised on the location of the bud of a plant during seasons with adverse conditions, i. e. cold seasons and dry seasons:

Phanerophyte

These plants, normally woody perennials, grow stems into the air, with their resting buds being more than 50 cm above the soil surface,[10]e.g. trees and shrubs, and also epiphytes, which Raunkiær later separated as a distinct class (see below).

Raunkiær further divided the phanerophytes according to height as

Megaphanerophytes,

Mesophanerophytes,

Microphanerophytes, and

Nanophanerophytes.

Further division was premised on the characters of duration of foliage, i. e. evergreen or deciduous, and presence of covering bracts on buds, for 8 classes. 3 further divisions were made to increase the total of classes to 12:

Phanerophytic stem succulents,

Phanerophytic epiphytes, and

Phanerophytic herbs.

Epiphytes

Epiphytes were originally included in the phanerophytes (see above) but then separated because they do not grow in soil, so the soil location is irrelevant in classifying them.

Chamaephytes

These plants have buds on persistent shoots near the soil surface; woody plants with perennating buds borne close to the soil surface, a maximum of 25 cm above the soil surface, e.g., bilberry and periwinkle.

Hemicryptophytes

Hemicryptophytes

These plants have buds at or near the soil surface, e.g. common daisy and dandelion, and are divided into:

Protohemicryptophytes: only cauline foliage;

Partial rosette plants: both cauline and basal rosette foliage; and

Dr. Archana Singh

5

Rosette plants: only basal rosette foliage.

Cryptophytes]

These plants have subterranean or under water resting buds, and are divided into:

Geophytes: rest in dry soil as a rhizome, bulb, corm, et cetera, e.g. crocus and tulip, and are subdivided into:

o Rhizome geophytes,

o Stem-tuber geophytes,

o Root-tuber geophytes,

o Bulb geophytes, and

o Root geophytes.

Helophytes: rest in marshy or wet soil, e.g. reedmace and marsh-marigold; and

Hydrophytes: rest submerged under water, e.g. water lily and frogbit.

Therophytes

These are annual plants that complete their lives rapidly in favorable conditions and survive the unfavorable cold or dry season in the form of seeds. Many desert plants are by necessity therophytes.

Aerophytes

Aerophytes were a later addition to the system.[11] These are plants that obtain moisture and nutrients from the air and rain. They usually grow on other plants yet are not parasitic on them. These are perennial plants whose roots atrophy. Some can live on mobile sand dunes. Like epiphytes and hemicryptophytes, their buds are near the soil surface. Some Tillandsia species are classified as aerophytes.

Expected Questions based on Raunkier’s Life Form

• What does this set-up demonstrate?

• On what basis is the distribution made?

• Name the different forms with one example each.

• What does this set-up demonstrate?

• Name the scientist who has given this classification?

• Describe the various forms shown with example

Dr. Archana Singh

6

3.HYDROSERE

Hydrosere is the primary succession which develops in aquatic environments such as lakes and

ponds. It results in conversion of water body and its community into a land community. In time,

a area of open freshwater will naturally dry out, ultimately becoming woodland. During this

change, a range of different land types such as swamp and marsh will succeed each other.

Important characteristics of Hydrosere are :

1) they usually start from a pond

2) phytoplanktons are the pioneer community

3) a forest or a grassland will be the climax community

4) it includes several seral stages of plant and animal communities

5) seral communities of plants are more obvious than animals

Hydrosere

It is a type of succession taking place in an aquatic environment. In a virgin

pond, hydrosere starts with a colonization of phytoplanktons and finally reaches a

climax forest stage. The different stages of succession are given below.

Dr. Archana Singh

7

1. Phytoplankton Stage

This is the initial stage of succession. Phytoplanktons, and zooplanktons are the

pioneer colonizers. These organisms add large amount of organic matter and

nutrients, which settle at the bottom of pond.

2. Rooted submerged stage

As a result of death and decomposition of phytoplanktons a soft mud develops at

the bottom of pond. This new habitat now becomes suitable for the growth of

rooted hydrophytes like Myriophyllum, Elodea, Hydrilla,

Potomogetan, Vallisneria, Utricularia etc. These plants further build up the

substratum. This new habitat now replaces these plants giving way to another type

of plants of floating types.

3. Floating stage

In the beginning the submerged and floating plants grow intermingled but very

soon the submerged plants are replaced completely. The habitat becomes changed

chemically as well as physically. The dead remains of plants are deposited at the

bottom. The substratum rises up in vertical direction. The important plants of this

stage are Nelumbium, Trapa, Pistia, Nymphaea andLimnanthemum.

4. Reed-swamp stage

This stage is also known as 'amphibious' stage as the plants of this community

are rooted but most parts of their shoots remain exposed to air, species

of Scirpus, Typha, Sagittaria and Phragmites etc. are chief plants of this stage.

Their rhizomes form a dense vegetation. The water level is very much reduced and

becomes unsuitable for growth of these amphibious species.

Dr. Archana Singh

8

5. Sedge meadow stage

Further decrease in water level changes the nature of substratum. Species of

some Cyperaceae and Gramineae such as Carex, Juncus,

Cyperus and Eleocharis colonise the area to form marsh or swamp. Thus mesic

conditions approach the area and marshy vegetation disappear gradually.

6. Woodland stage

In the beginning some shrubs and later medium sized trees form open

vegetation or woodland. These plants produce more shade. They render the habitat

more dry. The prominent plants of woodland community are species

of Butea, Acacia, Cassia, Terminalia, Salix, Cephalanthus etc.

7. Forest stage

This is the climax community invaded by several trees. In tropical climate with

heavy rainfall there develop tropical rain forests. In temperate regions, mixed

forest of Almus, Acer and Quercus are formed.

Expected Questions based Hydrosere

• What does this set-up demonstrate?

• Where is it generally studied?

• Which stage is called Amphibious stage? Write an example.

• Define climax community. Which stage depicts climax stage in the given set-up?

• Describe all the stages with example?

Dr. Archana Singh

9

4. LITHOSERE

Dr. Archana Singh

10

Biotic succession on bare rock (Lithosere, Xerosere).

The sequence of successional stages that occur on bare rocks is called lithosere. Because the bare

rock is deficient in water, the lithosere is also called xerosere.

The various seral stages are as follows :

(1) Lichen stage : Bare rock is invaded first by crustose lichens (e.g., Graphis). They corrode the

rock at places causing foliose lichens to invade, eliminate crustose lichens and creating

conditions for invasion by mosses. In tropics, blue green algae are pioneers instead of lichens.

(2) Moss stage : Mosses are of larger size, have gregareous habit and their rhizoids penetrate

deeper in the rocks. They shade the lichens and hence replace the same. Mosses accumulate

more soil and organic matter.

(3) Annual grass stage : Annual hardy grasses and herbs invade the humus rich moss dominated

rock surface, e.g., Aristida, Poa. Their roots cause fragmentation of the rock, creating more soil,

humus and moisture.

This increases moisture and soil. The soil becomes favourable for growth of longer lived annual

grasses. The process of soil accumulation continues.

(4) Perennial grass stage : Annual grasses are replaced by perennial grasses due to increased

moisture and soil in the rock crevices. The perennial grasses have runners and rhizomes which

rapidly spread the grasses, e.g., Cymbopogon, Heteropogon, Shade, moisture, soil, perennial

vegetation and seeds invite several small animals.

(5) Shrub stage : Shrubs begin to grow in area occupied by perennial grasses, e.g., Zizyphus,

Caparis, Rhus, Rubus. Shrubs are larger and their roots reach greater depth causing further

cracks in the rock substratum and hence helping in more soil formation. The shrubs shade the

area, make it more moist and invite hardy trees and several types of animals.

(6) Climax community : Initially hardy light demanding small trees invade the area. They make

the habitat shadier and more moist. Ultimately, trees shrubs and herbs representing the climax

community begin to grow in the area.

Expected Questions based Lithosere

What does this set-up demonstrate?

Describe all the stages shown in the set up with examples?