Ecosystem Test 1

The natural reservoir of phosphorous is rock, which contains phosphorus in the form of phosphates. Sea water, animal bones and fossils are reservoirs of carbon.

Xerarch refers to series of developmental stages in an arid area like bare rock. Lichen stage is the first stage in Lithosere (or succession on bare rock).

The community begins with relatively few pioneering plants and animals and develops through increasing complexity until it becomes stable or self-perpetuating as a climax community. The "engine" of succession, the cause of ecosystem change, is the impact of established species upon their own environments.

• Secondary succession is a process started by an event (e.g., forest fire, harvesting, hurricane) that reduces an already established ecosystem (e.g., a forest or a wheat field) to a smaller population of species and as such secondary succession occurs on preexisting soil. 
• Secondary biotic succession occurs in abandoned farm lands, burned or cut forests and lands that have been flooded. It is not similar to primary succession and neither it follows primary succession. It does not begins on bare rock as well. 

Phosphorus is a chemical element found on Earth in numerous compound forms, such as the phosphate ion (PO₄^3-), located in water, soil, and sediments.

The quantities of phosphorus in soil are generally small, and this often limits plant growth. That is why people often apply phosphate fertilizers on farmland. Animals absorb phosphates by eating plants or plant-eating animals.

Azospirillum is a nitrogen-fixing bacterium in paddy fields. It is a very useful soil and root bacterium. It is an associative symbiotic N₂ -fixing bacteria. When it is added to the soil, it multiplies in millions and can supply 20-40 Kg of nitrogen per hectare, per season.

Nutrients ultimately are chemical compounds. So, there is this natural pathway where the living matter is constantly circulated.

Nutrients are never lost from an ecosystem. Recycling of these nutrients happens at every stage, known as the nutrient cycle or biogeochemical cycle.

• Denitrifying bacteria, microorganisms whose action results in the conversion of nitrates in soil to free atmospheric nitrogen, thus depleting soil fertility and reducing agricultural productivity.
• Pseudomonas aeruginosa can, under anaerobic conditions (as in swampy or water-logged soils), reduce the amount of fixed nitrogen (as fertilizer) by up to 50 percent.

Ecological pyramids are the graphical representation of the trophic structure and function at successive trophic levels.
Ecological pyramids are of three general types:
(i) Pyramid of numbers, showing the number of organisms at each level.
(ii) Pyramid of biomass, showing the total dry weight of living matter.
(iii) Pyramid of energy, showing the rate of energy flow/productivity at successive trophic levels.

Hence, option C is correct.

Compensatory adjustment of organism to change in the environment, in nature or natural condition is known as acclimatization. Adjustment to seasonal changes in temperature come under acclimatization.