Ecosystem

 Lecture 3 Ecosystem

Ecosystem is a geographical area where biotic and abiotic factors work in an integrated manner and as an independent functional unit of nature.

The ecosystem can be broadly classified in two group

1. Terrestrial Ecosystem
2. Aquatic Ecosystem  

Standing crops- The amount of living biomass in an ecosystem expressed in biomass of organism per unit area

Standing state- The amount of nutrients present in the soil at any given time.

Components of Ecosystem

Ecosystem(Abiotic) 

Abiotic components determine and restrict the population growth and diversity of biotic factors in an ecosystem. It acts as a limiting factor. Ex- air, light, soil, nutrients, temperature and rainfall. 

Soil(Related terms) 

• Pedology- soil science (formation, evolution and soil modelling) 
• Edaphology- effect of soil on living beings(Plants) 
• Eluviation- transportation of soil materials from upper level to lower level soil. 
• Illuviation- accumulation of transported materials in lower level soil. 

Ecosystem(Biotic) 

Autotrophs- 

• Phototrophs(derived energy from light) 
• Chemotrophs(derived energy from chemicals) 
• Chemoautotrophs(derived energy from inorganic chemicals) 

Heterotrophs- 

Consumer- Primary consumer derived energy directly from producer or autotroph by consuming it. Secondary consumers derived energy from primary consumers. 

Decomposer- derived energy from waste or dead organism

• Detritivores derived energy from dead organisms(by eating). 
• Scavengers derived energy from feces. 
• Saprophyte release enzymes on dead organism to get energy 

Decomposition Process

Factors affecting decomposition

• Chemical composition of detritus
• Temperature
• Moisture
• Aeration
• Soil pH

Ecosystem(Biotic- Autotrophs)

Autotrophs(plants) are basic unit of an ecosystem and act as a energy cell of the ecosystem. Plants generate the chemical energy from sunlight which become the base for other lives. 

Types of Plants(Based on location) 

1. Aquatic       2. Terrestrial     3. Aerial

Based on lifespan

• Annual Plants- seasonal plants(wheat, rice, millet) 
• Biennial Plants- plant with 2 years life period
• Perennial Plants- plants with lifespan of more than 2 years

Based on appearance

• Herbs(small size, soft stem) 
• Shrubs(medium size, woody) 
• Tree(tall, woody) 
• Creeper(horizontal growth) 
• Climber(upright growth) 

Based on environmental conditions

• Xerophytes- plants that can survive arid/dry conditions
• Mesophytes- plants that can survive semi arid conditions(moderate water supply- good environment) 
• Hydrophytes- plants that can survive aquatic conditions
• Halophytes- plants that can survive salty water conditions (Mangroves) 

German biologist, August W. Eichler(1839-1887) developed a new system of classification of plants based on evolution(Plants Taxonomy) 

Vascular tissues- Complex tissues for transportation of fluids and nutrients in plant body

• Xylem- Dead cell and star shape hollow to allow water and nutrients from root to other parts(Outer layer of bark- Unidirectional) 
• Phloem- Active cell for transporting food(Inner layer of bark- Bidirectional) 

Some Facts

• Largest angiosperm tree- Eucalyptus
• Smallest angiosperm tree- Wolfia(group of aquatic plants) 
• Largest seed- Lodoicea maldivica
• Largest leaf- Victoria(aquatic plant)

Angiosperm Flower

• Female Part- Stigma, Style and Ovary
• Male Part- Anther, Filament and Pollen

Histology(Study of Tissues) 

Plant Tissues- shoot system (above ground) and root system (below ground) 

Simple permanent supportive tissues

• Parenchyma- Photosynthesis + food storage
• Collenchyma- It provides mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing sugar and storing it as starch. 
• Sclerenchyma- thick-walled, dead cells(because of Lignin) 

Simple permanent protective tissues

• Epidermis/Surface tissue- It is the outer layer of entire surface of plant. 
• Periderms- outer layer of stem act as protecting tissue during secondary growth(lateral growth). The periderms has three layers- phelloderm(living), phellogen, phellem(dead cell) 

Cork/Phellem- outer layer of stems and roots(impermeable to water and gases) 

Complex permanent tissue(Vascular tissues) 

• Xylem- Transport of water and nutrients from root to other parts of plant(Unidirectional) 
• Phloem- Food transportation tissues(Bidirectional) 

Plant Hormones

Ecosystem(Energy Flow- Productivity)

Rate of formation of biomass(energy) in the ecosystem. Productivity is expressed in units of mass per unit volume (or surface) per unit time.

There are two types of ecosystem productivity

• Primary Productivity- Generation of biomass from autotrophs(plants)        
• Secondary Productivity- Generation of biomass from heterotrophs(animals). The secondary productivity is that part of primary productivity which animals accumulated from plants. 

The average ocean productivity is about 50 grams carbon per square meter per year and the average land productivity is 160. Salt marshes and mangroves have one of the highest productivity of 3300- 6000. 

Sequence- Mangroves > Grasslands > Lakes > Oceans

Primary Production- Production of organic matter(energy) from inorganic carbon sources mainly by photosynthesis(Plants). This primary product supports life on earth and carbon cycle. 

 

      CO2+ Light → Organic matter + O2

Gross Primary Production(GPP)- Photosynthesis by all the plants in an ecosystem. 

Net Primary Production(NPP)- Energy lost in respiration by plants from total energy(GPP- Photosynthesis) 

              NPP= GPP- respiration(by Plants) 

Net Ecosystem Production(NEP)- Energy lost in respiration by all organisms(plant+ animals)of an ecosystem from total energy produced by an ecosystem. 

          NEP= GPP- respiration(Net ecosystem respiration) 

Net ecosystem production can be or cannot be equal to net carbon accumulation by an ecosystem. The equality depends on whether any stored CO2 gets released(carbon release other than respiration). 

Ecological Efficiency- Percentage of energy transferred from one trophic level to 

another in an ecosystem

Photosynthesis- 

1. Photoautotroph- use of light energy + CO2+ H2O

There are several bacteria that can conduct anoxygenic photosynthesis. Like green sulfur bacteria (GSB), red and green filamentous phototrophs (FAPs e.g. Chloroflexia), purple bacteria, acidobacteriota, and heliobacteria. 

6CO2+ 12H2S → C6H12O6+ 12S+ 6H2O

2. Photoheterotroph- use of light energy + organic matter from environment+ H2O

Ex- purple non-sulfur bacteria, green non-sulfur bacteria, and heliobacteria

Photosynthesis is the process of converting the visibl light energy into chemical energy by plants, algae, and cyanobacteria(blue-green algae). It happens in 2 stages- 1. Light dependent reaction(in thylakoid, NADPH and ATP) 2. Light independent reaction/Dark reaction(in stroma, Calvin cycle+Hatch-Stack cycle → Carbohydrate) 

6CO2+ 6H2O → C6H12O6(energy) + 6O2

Photosynthesis is performed by those proteins which contains Chlorophyll

Cell(Eukaryotic) → Chloroplast(Plastid) → Proteins → Chlorophyll

At protein level two types of protein complexs play role of light capturing in Photosynthesis- Photosystem 1(~680nm) and Photosystem 2(~700nm) 

In the plants there are two types of Chlorophyll dominate(in each photosystem) 

• Chlorophyll a(red, blue and violate light) 
• Chlorophyll b(mainly blue light) 

In low light condition, plants produce more chlorophyll b than Chlorophyll a. 

Both were poorer absorber of green light because of which plants look green. 

The Emerson effect is the increase in the rate of photosynthesis after chloroplasts are exposed to the combined red spectrum of light (upto 680 nm) and far red spectrum (more than 680 nm). If photosynthesis rate at 680nm is A and photosynthesis rate at 700nm is B, then photosynthesis rate when plant is exposed to both light will be greater than A+B.

The photosynthesis efficiency is that portion of absorbed light which get converted into chemical energy by plants. 

Ecosystem(Energy Flow- Limiting Factors)

There are various factors that limits the rate of Photosynthesis(energy flow in ecosystem)

Light, Leaf area(plant portion involved in photosynthesis), CO2, Water, Temperature

Phototropism- Growth of organism in response to light stimulus because of Auxin hormones. 

Thigmotropism- Plant moves or grow in response to touch stimulus. 

Ecosystem(Nutrients Cycle)

A nutrient is a substance that helps the organism to survive, grow, and reproduce. Like water is essential for survival of any organism. Energy flow is part of nutrient flow. 

The nutrients can be classified in two groups based on source

1. Essential nutrients- cannot be synthesis by organism and require intake
2. Non Essential nutrients- also required for survival but can be synthesis by organism

Another classification is based on required quantity of nutrients

1. Macro Nutrients- large quantities required to survive(Human- Carbohydrate, Protein and Fat. These three nutrients provide energy to human being other macro nutrients are water and dietary fiber) 
2. Micro Nutrients- essential nutrients required in small quantities(Human- vitamin and minerals for metabolism, Plants- Minerals) 

Nutrient cycle is exchange of matter(organic + inorganic) between biotic and abiotic components of an ecosystem. 

The cycles of water, carbon, oxygen, nitrogen, phosphorus etc are also known as biogeochemical cycle(exchange of Chemical element between biotic and atmospheric components) 

Nutrient cycle is of two types based on mineral reservoir

1. Gaseous cycle(Water, C, O, N cycle) 
2. Sedimentary cycle(P, S, Ca, Mg cycle) 

Nitrogen Cycle- Transformation of nitrogen and nitrogen containing compounds in nature. It is a cycle which includes gaseous components.

Water Cycle(Hydrological Cycle)- Movement of water on, above and below the surface of the Earth in states such as liquid, vapour and ice. 

Carbon Cycle- Biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere and atmosphere of the Earth.

Oxygen Cycle- Movement of oxygen within and between its three main reservoirs- the atmosphere, the biosphere and the lithosphere. The main driving factor of the oxygen cycle is photosynthesis responsible for the Earth's atmospheric composition and life.

Phosphorus Cycle(Sedimentary Cycle)- Movement of phosphorus through the lithosphere, hydrosphere and biosphere. The atmosphere does not play a significant role in the movements of phosphorus as phosphorus and phosphorus compounds are usually solids at normal temperature and pressure of environment.

 Factors affecting Ecosystem

Ecosystem is controlled by both external and internal factors. 

External factors(state factors)- control the overall structure of an ecosystem. By controlling resource inputs. Ex- Climate, Soil parent material, Topography, 

Internal factors- controlled ecosystem process as well as get controlled by it. The availability of resources in an ecosystem is controlled by internal factors. Ex- Eological Transition, Ecological succession

Ecosystem Services

Values derived from ecosystem

Table of Contents                                               Lecture 4