Primary And Secondary Producers 64112j

ENVIRNOMENTAL SCIENCE REPORT PRODUCERS : PRIMARY AND SECONDARY

V. Venkatesh Kumar DTU/2K13/B03/0453

CONTENTS 1.

Introduction

2.

Role Of Producers

3.

Primary Producers o Gross And Net Primary Productivity o Terrestrial Production o Terrestrial Primary Production Over Time o Oceanic Production o Factors Limiting Primary Production o Nutrients

4.

Secondary Productivity





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INTRODUCTION Any unit or bio system that includes all the organisms which function together in a given area where they interact with the physical environment is known as ecosystem. The ecosystem is the functional unit in ecology as it consists of both the biotic community (living organisms) and abiotic environment. The latter have close interaction, essential for maintenance of life processes. Energy, water, nitrogen and soil minerals are essential abiotic components of an ecosystem. Figure: Food Chain

In an ecosystem, producers are autotrophic organism that use photosynthesis to capture energy by using sunlight, water and carbon dioxide to create carbohydrates, and then use that energy to create more complex molecules like proteins, lipids and starches that are crucial to life processes. Producers, which are mostly green plants, are also called Autotrophs.

ROLE OF PRODUCERS Autotrophs are fundamental to the food chains of all ecosystems in the world. They take energy from the environment in the form of sunlight or inorganic chemicals and use it to create energy-rich molecules such as carbohydrates. This mechanism is called primary production. Other organisms, called heterotrophs, take in autotrophs as food to carry out functions necessary for their life. Thus, heterotrophs — all animals, almost all fungi, as well as most bacteria and protozoa — depend on autotrophs for the energy and raw materials they need. Heterotrophs obtain energy by breaking down organic molecules (carbohydrates, fats, and proteins) obtained in food. Carnivorous organisms ultimately rely on autotrophs because the nutrients obtained from their heterotroph prey come from

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autotrophs they consumed. Thus, every other organism depends on producers directly or indirectly for survival. Also at each step, energy is lost. Less than 10 percent of the energy stored in plants is converted to herbivore mass. The loss from herbivore to predator is similar. Thus energy needs to be added to the ecosystem continuously.

Figure: Cynobacteria (Blue Green Algae)- Producer

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PRIMARY PRODUCERS Autotrophic organisms that synthesize organic materials from inorganic materials, effectively introducing new organic material into the environment so that the primary consumers can feed upon and so forth are known as Primary Producers. Primary Production is defined as the amount biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It occurs through the process of photosynthesis where it uses light as a primary source of energy. It also occurs by the process of chemosynthesis, which uses the oxidation or reduction of chemical compounds as its source of energy. It is expressed in of weight (g–2) or energy (kcal m–2). The following two equations are simplified representations of photosynthesis (top) and (one form of) chemosynthesis (bottom): CO2 + H2O + light

CH2O + O2

CO2 + O2 + 4 H2S

CH2O + 4 S + 3 H2O

The rate of biomass production is called productivity. It is expressed in of g–2 yr– 1 or (kcal m–2) yr–1 to compare the productivity of different ecosystems. It can be divided into gross primary productivity (GPP) and net primary productivity (NPP).

GROSS AND NET PRIMARY PRODUCTIVITY Gross Primary Productivity (GPP) of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. ) Some fraction of this fixed energy is used by primary producers for cellular respiration and maintenance of existing tissues (i.e., "growth respiration" and "maintenance respiration"). This fixed energy is called Net Primary Productivity.

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Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP).

NPP = GPP – R (Respiration Loss) Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers).

TERRESTRIAL PRODUCTION On the land, almost all primary production is now performed by vascular plants, with a small fraction coming from algae and non-vascular plants such as mosses and liverworts. Primary production on land is a function of many factors, but principally depends on local hydrology and temperature. While plants cover much of the Earth's surface, they are strongly curtailed wherever temperatures are too extreme or where necessary plant resources are limiting, such as deserts or polar regions.

TERRESTRIAL PRIMARY PRODUCTION OVER TIME Terrestrial primary production fluctuates over time and is closely coupled with physical (i.e., abiotic) and ecological (i.e., biotic) changes that play out over different timescales. On scales of seconds to hours, primary production during the growing season responds to environmental drivers of photosynthesis, generally increasing with photosynthetic photon flux density (PPFD) or the spectrum of solar radiation available to power photosynthesis. Year-to-year, or interannual, changes in terrestrial primary production are often related to long-term climate variation including prolonged drought and, in some cases, variation from one year to the next in average annual temperature and solar radiation.

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Over decades, a period that is meaningful to ecological succession, terrestrial primary production changes in response to shifts in plant competition and disturbance. Consider an abandoned field that undergoes a successional reversion back to forest. Plant communities will assemble during early succession, with fast-growing plants emerging first and because of low initial plant density there will be little competition for resources. As a result, total plant growth in the ecosystem, or NPP, will proceed at an increasingly higher rate for several years. NPP generally levels off or declines once plants start crowding one another and begin competing more intensively for limiting light, nutrient, and water resources (Figure 3). Terrestrial primary production also may change over time in response to natural disturbances such as insect outbreaks, wind, fire, and pathogens that diminish photosynthesis by reducing leaf biomass and causing plant death. Long-term increases in atmospheric CO2 and nitrogen deposition associated primarily with fossil fuel burning generally increase plant growth over long periods of time.

OCEANIC PRODUCTION In a reversal of the pattern on land, in the oceans, almost all photosynthesis is performed by algae, with a small fraction contributed by plants and other groups. Algae encom a diverse range of organisms, ranging from single floating cells to attached seaweeds. They include photoautotrophs from a variety of groups. Eubacteria are important photosynthetizers in both oceanic and terrestrial ecosystems, and while some archaea are phototrophic, none are known to utilize oxygen-evolving photosynthesis. A number of eukaryotes are significant contributors to primary production in the ocean, including green algae, brown algae and red algae, and a diverse group of unicellular groups. Vascular plants are also represented in the ocean by groups such as the sea grasses.

FACTORS LIMITING PRIMARY PRODUCTION The availability of water, obviously, is not an issue. Temperature, while affecting metabolic rates, ranges less widely in the ocean than on land because the heat capacity of seawater buffers temperature changes, and the formation of sea ice insulates it at lower temperatures. However, the availability of light, the source of

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energy for photosynthesis, and mineral nutrients, the building blocks for new growth, play crucial roles in regulating primary production in the ocean.

NUTRIENTS Inorganic nutrients, such as nitrate, phosphate and silicic acid are necessary for phytoplankton to synthesise their cells and cellular machinery. Because of gravitational sinking of particulate material, nutrients are constantly lost from the photic zone (sunlit zone of ocean), and are only replenished by mixing or upwelling of deeper water.

SECONDARY PRODUCTIVITY Secondary productivity is defined as the rate of formation of new organic matter by consumers. Secondary productivity serves as an index of significance of the population in of food resources available to the heterotrophic populations, including man, in the food chain. Herbivores and carnivores ingest the food material where a part of this is assimilated and a part is egested. A large part of assimilated food (energy) is utilised for metabolism (largely respiration), growth, reproduction, maintenance of body and other activities. Remaining part is stored in somatic and reproductive tissues and thus compared to net production. Secondary productivity by decomposer organisms (in a detritus food chain) is different. Here the matter is recycled and microorganisms show a high growth rate. Community productivity is 'the rate of net synthesis or built up of organic matter by a community per unit time and area'.

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