Evolution is one of the Biology Topics that has been debated and studied for centuries, exploring the process by which species change over time.
Explore How Productivity in the Ecosystem Works – Process, Factors Affecting Decomposition
At a particular area and unit of time and at any trophic level, the amount of the synthesis of energy in the organic matter is called productivity. Productivity also refers to the amount of organic matter or biomass produced by an individual organism, population, community, or ecosystem during a given period of time. Productivity is divided into the following two types.
1. Primary Productivity
Primary production refers to all or any part of the energy fixed by plants possessing chlorophyll. Primary production is further divided into Gross Primary Production and Net Primary Production.
(a) Gross Primary Production:
The total amount of solar energy converted (fixed) into chemical energy by green plants (by the process of photosynthesis), is called ‘Gross Primary Production’ (GPP). The rate at which, organic matter is synthesized by producers per unit of time and area, is also called ‘Gross Primary Production’ (GPP).
(b) Net Primary Production:
A certain portion of gross primary production is utilized by plants for maintenance (largely respiratory energy loss) and the remainder is called ‘Net Primary Production (NPP)’ which appears as new plant biomass.
‘The rate of organic matter build-up or stored by producers in their bodies per unit time and area is called ‘Net Primary Production (NPP)’.
GPP – Energy lost by respiration and maintenance = NPP
The biochemical formula that describes photosynthesis is
Primary production is of special importance in ecology since it is the energy fixed by plants by converting solar energy into chemical energy of food material that supports life in other trophic levels.
2. Secondary Productivity
Secondary production refers to the net quantity of energy transferred and stored in the somatic and reproductive tissues of heterotrophs over a period of time. Some heterotrophs (consumers and decomposers) feed on the net. Primary production and some on other heterotrophic organisms. Thus, productivity by heterotrophic organisms in the ecosystem is called secondary productivity.
The rate of increase in the biomass of heterotrophs per unit time and area is called secondary productivity. Secondary productivity serves as an index of the significance of the population in terms 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 utilized for metabolism (largely respiration), growth, reproduction, maintenance of the body, and other activities. The 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’.
The carbon and nutrients in dead organic matter are broken down by a group of processes known as decomposition. This releases nutrients that can be reused for plant and microbial production and returns carbon dioxide to the atmosphere (or water) where it can be used for photosynthesis. In the absence of decomposition, dead organic matter would accumulate in an ecosystem, and nutrients and atmospheric carbon dioxide would be depleted. Approximately 90% of terrestrial NPP goes directly from plant to decomposer.
Steps of Decomposition (Processes and Products)
Decomposition processes can be separated into three categories leaching, fragmentation, and chemical alteration of dead material.
As water moves through dead organic matter, it dissolves and carries it with the water-soluble components. These are then taken up by organisms in the soil, react with mineral soil, or are transported beyond the confines of the ecosystem (and are considered “lost” to it). Newly shed leaves and newly dead animals have high concentrations of water-soluble components and include sugars, amino acids, and mineral nutrients. Leaching is more important in wet environments, and much less important in dry ones.
Fragmentation processes break organic material into smaller pieces, exposing new surfaces for colonization by microbes. Freshly shed leaf litter may be inaccessible due to an outer layer of cuticle or bark, and cell contents are protected by a cell wall. Newly dead animals may be covered by an exoskeleton. Fragmentation processes, which break through these protective layers, accelerate the rate of microbial decomposition. Animals fragment detritus as they hunt for food, as does passage through the gut. Freeze-thaw cycles and cycles of wetting and drying also fragment dead material.
3. The Chemical Alteration or Catabolism:
The chemical alteration of dead organic matter is primarily achieved through bacterial and fungal action. Fungal hyphae produce enzymes that can break through the tough outer structures surrounding dead plant material. They also produce enzymes that break down lignin, which allows them access to both cell contents and the nitrogen in the lignin. Fungi can transfer carbon and nitrogen through their hyphal networks and thus, unlike bacteria, are not dependent on locally available resources.
It is the process of the formation of a dark-colored layer of substance on the soil, which is amorphous, called humus. It cannot be decomposed easily because it is highly resistant to action by microbes. The hummus is very rich in nutrients as it provides high fertility to the soil.
It is the final step of the process. It is the process of degradation of the humus to release inorganic nutrients.
Factors Affecting Decomposition
Decomposition rates vary among ecosystems. The rate of decomposition is governed by three sets of factors – the physical environment (temperature, moisture, and soil properties), the quantity and quality of the dead material available to decomposers, and the nature of the microbial community itself.
Temperature controls the rate of microbial respiration; the higher the temperature, the faster microbial decomposition occurs. It also affects soil moisture, which slows microbial growth and reduces leaching. Freeze-thaw cycles also affect decomposition freezing temperatures and kill soil microorganisms, which allows leaching to play a more important role in moving nutrients around. This can be especially important as the soil thaws in the Spring, creating a pulse of nutrients that become available.
2. Soil and Moisture:
Decomposition rates are low under very wet or very dry conditions. Decomposition rates are highest in wet, moist conditions with adequate levels of oxygen. Wet soils tend to become deficient in oxygen (this is especially true in wetlands), which slows microbial growth. In dry soils, decomposition slows as well, but bacteria continue to grow (at a slower rate) even after soils become too dry to support plant growth. When the rains return and the soils become wet, the osmotic gradient between the bacterial cells and the soil water causes the cells to gain water quickly. Under these conditions, many bacterial cells burst, releasing a pulse of nutrients.
3. Soil pH:
Decomposition rates also tend to be slower in acidic soils. Soils that are rich in clay minerals tend to have lower decomposition rates, and thus, higher levels of organic matter.
4. Soil Particle Size:
The smaller particles of clay result in a larger surface area that can hold water. The higher the water content of the soil, the lower the oxygen content and consequently, the lower the rate of decomposition. Clay minerals also bind particles of organic material to their surface, making them less accessible to microbes. Soil disturbance like tilling increases decomposition by increasing the amount of oxygen in the soil and by exposing new organic matter to soil microbes.
5. Chemical Nature of Detritus:
The quality and quantity of the material available to decomposers in another major factor that influences the rate of decomposition. Substances like sugars and amino acids decompose readily and are considered “labile”. Cellulose and hemicellulose, which are broken down more slowly, are “moderately labile”. Compounds that are more resistant to decay, like lignin or cutin are considered “recalcitrant”. Litter with a higher proportion of labile compounds decomposes much more rapidly than litter with a higher proportion of recalcitrant material. Consequently, dead animals decompose more rapidly than dead leaves, which themselves decompose more rapidly than fallen branches.