● The organisms need a `color{violet}"constant supply of nutrients"` to grow, reproduce and regulate various body functions.

● The amount of nutrients, such as `color{violet}"carbon, nitrogen"`, `color{violet}"phosphorus, calcium"`, etc., present in the soil at any given time, is referred to as the `color{brown}"standing state"`.

● It varies in different kinds of `color{violet}"ecosystems"` and also on a `color{violet}"seasonal basis"`.

● What is important is to appreciate that nutrients which are `color{violet}"never lost"` from the ecosystems, they are `color{violet}"recycled"` time and again indefinitely.

● The `color{violet}"movement of nutrient"` elements through the various components of an ecosystem is called `color{brown}"nutrient cycling"`.

● Another name of nutrient cycling is `color{brown"biogeochemical cycles"` (bio: living organism, geo: rocks, air, water).

● Nutrient cycles are of two types: (a) `color{brown"gaseous"` and (b) `color{brown"sedimentary"`.

● The `color{violet}"reservoir for gaseous"` type of nutrient cycle (e.g., nitrogen, carbon cycle) exists in the `color{violet}"atmosphere"` and for the `color{violet}"sedimentary cycle"` (e.g., sulphur and phosphorus cycle), the reservoir is located in `color{violet}"Earth’s crust"`.

● `color{violet}"Environmental factors"`, e.g., soil, moisture, pH, temperature etc., `color{violet}"regulate"` the rate of release of nutrients into the atmosphere.

● The `color{violet}"function"` of the reservoir is to `color{violet}"meet with the deficit"` which occurs due to imbalance in the rate of influx and efflux.

● For the composition of `color{violet}"living organisms"`, `color{brown}"carbon"` constitutes `color{violet}"49 per cent of dry weight"` of organisms and is next only to water.

● If we look at the total quantity of global carbon, we find that `color{violet}"71 per cent carbon"` is found dissolved in `color{violet}"oceans"`.

● This `color{violet}"oceanic reservoir"` regulates the amount of `color{violet}"carbon dioxide"` in the atmosphere.

● Also the `color{violet}"atmosphere"` only contains about `color{violet}"1 per cent"` of total global carbon.

● `color{violet}"Fossil fuel"` also represent a reservoir of carbon.

● Carbon cycling occurs through `color{violet}"atmosphere, ocean"` and through `color{violet}"living and dead organisms"`.

● According to one estimate `4 × 10^13 kg` of carbon is fixed in the biosphere through `color{violet}"photosynthesis annually"`.

● A considerable amount of `color{violet}"carbon returns"` to the atmosphere as `CO_2` through `color{violet}"respiratory activities"` of the producers and consumers.

●`color{violet}" Decomposers"` also contribute substantially to `CO_2` pool by their processing of `color{violet}"waste materials"` and dead organic matter of land or oceans.

● Some amount of the fixed carbon is `color{violet}"lost to sediments"` and removed from circulation.

● `color{violet}"Burning of wood"`, `color{violet}"forest fire"` and `color{violet}"combustion"` of organic matter, `color{violet}"fossil fuel"`, `color{violet}"volcanic activity"` are additional sources for releasing `CO_2` in the atmosphere.

● `color{violet}"Human activities"` have significantly influenced the carbon cycle.

● `color{violet}"Rapid deforestation"` and `color{violet}"massive burning"` of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere.

● `color{brown}"Phosphorus"` is a major constituent of `color{violet}"biological membranes"`, `color{violet}"nucleic acids"` and cellular `color{violet}"energy transfer systems"`.

● Many animals also need large quantities of this element to make `color{violet}"shells, bones and teeth"`.

● The `color{violet}"natural reservoir"` of phosphorus is `color{violet}"rock"`, which contains phosphorus in the form of `color{violet}"phosphates"`.

● When rocks are `color{violet}"weathered"`, minute amounts of these `color{violet}"phosphates dissolve"` in soil solution and are `color{violet}"absorbed by the roots"` of the plants.

● `color{violet}"Herbivores"` and other animals obtain this element from `color{violet}"plants"`.

● The `color{violet}"waste products"` and the dead organisms are decomposed by `color{violet}"phosphate-solubilising bacteria"` releasing phosphorus.

● Unlike carbon cycle, there is `color{violet}"no respiratory release"` of phosphorus into atmosphere.

● The other two major and `color{violet}"important differences"` between carbon and phosphorus cycle are firstly, `color{violet}"atmospheric inputs"` of phosphorus through rainfall are `color{violet}"much smaller"` than carbon inputs, and, secondly, `color{violet}"gaseous exchanges"` of phosphorus between organism and environment are `color{violet}"negligible"`.

● `color{violet}"Healthy ecosystems"` are the base for a wide range of `color{violet}"economic, environmental"` and `color{violet}"aesthetic"` goods and services.

● The `color{violet}"products of ecosystem"` processes are named as `color{brown}"ecosystem services"`.

● `color{brown}"For example"`, healthy forest ecosystems `color{violet}"purify air and water"`, mitigate `color{violet}"droughts and floods"`, cycle `color{violet}"nutrients"`, generate `color{violet}"fertile soils"`, provide `color{violet}"wildlife habitat"`, maintain `color{violet}"biodiversity"`, `color{violet}"pollinate crops"`, provide `color{violet}"storage site"` for carbon and also provide `color{violet}"aesthetic, cultural"` and `color{violet}"spiritual values"`.

● Though `color{violet}"value"` of such services of biodiversity is `color{violet}"difficult to determine"`, it seems reasonable to think that biodiversity should carry a `color{violet}"hefty price tag"`.

● `color{brown}"Robert Constanza"` and his colleagues have very recently tried to put price tags on `color{violet}"nature’s life-support"` `color{violet}"services"`.

● Researchers have put an average price tag of `color{violet}"US $ 33 trillion a year"` on these `color{violet}"fundamental ecosystems services"`, which are largely taken for granted because they are free.

● This is nearly `color{violet}"twice the value"` of the `color{violet}"global"` gross national product `color{violet}"GNP"` which is (US $ 18 trillion).

● Out of the total cost of various ecosystem services, the `color{violet}"soil formation"` accounts for about `color{violet}"50 per cent"`, and contributions of other services like `color{violet}"recreation"` and `color{violet}"nutrient cycling"`, are `color{violet}"less than 10 per cent"` each.

● The cost of `color{violet}"climate regulation"` and `color{violet}"habitat for wildlife"` are about `color{violet}"6 per cent"` each.