Carbon Cycle.pptx

• Carbon cycle • Organic matter decomposition • Humus formation

• Atmosphere • Biosphere • Geosphere

CARBON CYCLE The series of processes by which carbon compounds are interconverted in the environment, involving the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels.

CC in nature comprises of two main processes: • (i) The conversion of oxidized form of carbon into reduced organic form by photosynthetic organisms, and • (ii) Restoration of original oxidized form through mineralization of the organic form by the micro-organisms.

Conversion of Oxidized form of Carbon (CO2) into Reduced Organic Form:

By the process of photosynthesis. Photosynthetic algae and higher plants are the most important agents. In the ocean the free floating algae called phytoplanktons. estimated to fix annually about 1.2 x 1010 tons of carbon. Nearly 1.6 x 1010 tons of carbon is said to be fixed annually by photosynthetic terrestrial plant life.

Schematic representation of CC

CO2 + 2H2 → (CH2O)x + H2O

2. Restoration of Original Oxidized Form (CO2) through Mineralization of the Organic Form:

Three different modes through which the organic matter is mineralizes and the CO2 is released in the atmosphere. (i) Process of respiration, (ii) Accidental (forest fire) and intentional (fuel) burning. (iii) Decomposition of organic matter by microorganisms.

Decomposition of OM by MOs: The organic carbon compounds that eventually are deposited in the soil are degraded by the activities of microorganisms which are mainly the bacteria and fungi. The CO2 is released into the air and soil.

(i) Cellulose Decomposition (ii) Hemicellulose Decomposition (iii) Lignin Decomposition

(i) Cellulose Decomposition Summarized as,

• The fungi which decompose cellulose in soil are mainly Trichoderma, Aspergillus, Penicillium, Fusarium, Chaetomium, Verticillium. Rhizoctonia, Myrothecium, Merulius, Pleurotus, Fomes, etc. • The bacteria that bring about cellulose decomposition in soil consist mainly of the species of Clostridium, Cellulomonas, Streptomyces, Cytophaga, Bacillus, Pseudomonas, Nocardia, Micromonospora, Sporocytophaga, Polyangium, Cellfalcicula, etc.

(ii) Hemicellulose Decomposition • Hemicelluloses are the polymers of simple sugars such as pentoses, hexoses and uronic acid. Enzymes hemicellulases • The fungi that degrade hemicelluloses in soil are Chaetomium, Aspergillus, Penicillium, Trichoderma, Fusarium, Humicola, etc. • Bacillus, Pseudomonas, Cytophaga, Vibrio, Erwinia, Streptomyces, Actinomyces, etc. are the bacteria that degrade hemicelluloses in soil.

(iii) Lignin Decomposition It is highly resistant of microbial degradation. However, certain fungi Aspergillus, Penicillium, Fusarium, Lenzites, Clavaria, Polyporus, etc.) and bacteria (examplified by Streptomyces, Nocardia, Flavabacterium, Xanthomonas, Pseudomonas, Micrococcus, etc.) are known to degrade lignin at slow rates.

Humus • Humus has many nutrients that improve the health of soil, nitrogen being the most important. C:N of humus is 10:1. • Humus is a very complex substance. • Humus is different from decomposing soil organic matter. • Humus looks rough and has visible remains of the original plant or animal matter. • Fully humified humus, on the contrary, has a uniformly dark, spongy, and jelly-like appearance, and is amorphous; it may gradually decompose over several years or persist for millennia. • It has no determinate shape, structure, or quality.

Examined under a microscope, humus may reveal tiny plant, animal, or microbial

remains that have been mechanically, but not chemically, degraded.

Humus is an integral part of soil organic matter.