CBSE · Class 12 · Biology · EcosystemDiscuss nutrient cycling in ecosystems with special reference to the Carbon cycle. Explain the reservoir pool, gaseous cycle, and human impacts on the carbon cycle in detail.

Introduction to Nutrient Cycling\nNutrients are never lost from ecosystems; they are recycled indefinitely. The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycles. They are of two types: gaseous (e.g., carbon, nitrogen) and sedimentary (e.g., phosphorus, sulfur).

The Carbon Cycle\nCarbon is the fundamental building block of all organic molecules and constitutes 49% of the dry weight of organisms.

1. Distribution of Carbon:

   • 71% of global carbon is found dissolved in oceans, which acts as a major reservoir.
   • Atmosphere contains about 1% of total global carbon.
   • Fossil fuels also represent a massive carbon reservoir.

2. Pathways in Carbon Cycle:

   • Photosynthesis: Green plants absorb atmospheric/dissolved carbon dioxide ($CO_2$) to synthesize organic compounds, fixing carbon into the biotic components.
   • Respiration: Organic carbon is broken down by producers and consumers, releasing $CO_2$ back into the atmosphere.
   • Decomposition: Decomposers break down dead organic matter, returning carbon to the soil and air.
   • Combustion and Volcanic Activity: Burning of fossil fuels, wood, and organic debris rapidly releases huge amounts of $CO_2$ into the atmosphere.

3. Human Impact on the Carbon Cycle:

   • Rapid deforestation and massive burning of fossil fuels for energy and transport have drastically increased the concentration of $CO_2$ in the atmosphere.
   • This enhanced greenhouse effect is leading to global warming and serious climate changes globally.