noc19-bt09 Lecture 11-Primary Production

Understanding Primary Production in Ecological Energetics

What is Primary Production?

• Primary production refers to the synthesis of organic compounds from atmospheric or aqueous carbon dioxide through photosynthesis or chemosynthesis.

• Autotrophs are the organisms responsible for primary production, categorized into two types: photoautotrophs (using light) and chemoautotrophs (using chemical reactions).

The Role of Photoautotrophs

• Photoautotrophs utilize light for self-nutrition, converting carbon dioxide into organic molecules like carbohydrates, fats, and proteins.

• These organic molecules serve as energy sources when consumed by other organisms, transferring energy up the food chain.

Importance of Primary Production

1. Ecosystem Composition: Autotrophs constitute 99.9% of Earth's living mantle, highlighting their significance in ecosystems.

2. Energy Conversion: Primary production converts solar energy into biological energy that fuels entire ecosystems; without it, food chains would collapse.

3. Oxygen Release: As a by-product of primary production, oxygen is essential for most organisms to convert biological molecules into usable energy.

Processes Involved in Primary Production

• Plants perform both photosynthesis and respiration simultaneously; during photosynthesis, they convert carbon dioxide and water into glucose while releasing oxygen.

• Respiration reverses this process by breaking down glucose with oxygen to release carbon dioxide and water while generating ATP as energy.

Key Terms Related to Primary Production

Understanding Primary Production in Plants

What is Gross Primary Production?

• The concept of gross primary production (GPP) refers to the total amount of carbon dioxide fixed or energy captured through photosynthesis per unit time.

• GPP occurs alongside respiration in plant cells, where some carbon is fixed during photosynthesis and subsequently released during respiration.

• To determine net primary production (NPP), one must subtract the carbon lost via respiration from the GPP, indicating the actual energy available for growth.

Distinction Between Production and Productivity

• The terms "production" and "productivity" are often used interchangeably but have distinct meanings; production refers to the total amount fixed, while productivity indicates fixation per unit time.

• In literature, gross primary production can also be referred to as gross primary productivity when emphasizing fixation rates over time.

Compensation Point Explained

• The compensation point is defined as the equilibrium state where photosynthesis equals respiration, meaning no net gain or loss of carbon dioxide occurs.

• During daytime, both processes occur simultaneously; however, respiration continues at night when photosynthesis ceases due to lack of sunlight.

Analyzing Carbon Dioxide Dynamics Over Time

• A graph illustrating CO2 dynamics shows three regions:

• Region 1: Net release of CO2 occurs before sunrise (0 hours to ~6:15).

• Region 2: From ~6:15 to ~17:45, there’s a net absorption of CO2 due to active photosynthesis.

• Region 3: After ~17:45 until midnight, again a net release of CO2 happens as respiration exceeds photosynthesis.

Measuring Primary Production

• At compensation points occurring early morning and late evening, plants neither absorb nor release significant amounts of CO2 or O2.

Understanding Carbon Dioxide Utilization in Photosynthesis

Measuring Carbon Dioxide and Oxygen Exchange

• The process involves 2966 kilojoules of energy absorbed, utilizing 6 moles of carbon dioxide (equivalent to 134.4 liters at standard temperature and pressure) while releasing 6 moles of oxygen.

• To measure carbon dioxide fixation, one can cover a plant with a glass jar and track the CO2 levels throughout the day to determine how much has been utilized.

• Alternatively, measuring the amount of oxygen released by the plant can also estimate the fixed carbon dioxide or synthesized biological molecules.

Gross vs. Net Primary Production

• Gross primary production refers to total productivity without accounting for respiration losses, while net primary production considers carbon released during respiration.

• Using radioactive carbon dioxide (carbon-14), researchers can trace its incorporation into sugar molecules produced by plants, allowing estimates of CO2 absorption during photosynthesis.

Biomass Measurement Methodology

• A mixed approach using both carbon isotopes (carbon-12 and carbon-14) helps estimate sugars produced based on known initial ratios.

• The change in biomass (delta B = B2 - B1 between two time periods t1 and t2) is used to assess productivity in ecosystems like forests by estimating wood, leaves, roots, and litter.

Efficiency of Production

• The efficiency of gross primary production is calculated as energy fixed divided by incident sunlight energy; for example, if a plant intercepts 1000 calories but fixes only 40 calories through photosynthesis, it results in a gross efficiency of 4%.

Understanding Net Primary Productivity

Defining Efficiency and Productivity

• Net efficiency is calculated as 10 calories of net primary production divided by 1000 calories, resulting in a 1% efficiency.

• Productivity is defined as production per unit time; for example, if a forest produces 1 ton of biomass over 2 years, its productivity is 0.5 tons per year.

Calculating Net Primary Productivity

• The formula for net primary productivity (NPP) is NPP = APAR × LUE, where APAR stands for absorbed photosynthetically active radiation and LUE represents light use efficiency.

• APAR quantifies the energy absorbed by plants in megajoules per square meter over time, indicating how much sunlight contributes to photosynthesis.

Photosynthetically Active Radiation (PAR)

• PAR includes wavelengths primarily in the blue and red regions of the spectrum that are utilized for photosynthesis; green wavelengths are mostly reflected.

• The absorption of PAR leads to the generation of biomass through photosynthesis, with only specific wavelengths contributing effectively.

Factors Influencing NPP

• Light use efficiency measures how effectively plants convert absorbed light into carbon fixation, expressed in grams of carbon per megajoule.

• Geographic factors such as latitude and local topography affect the amount of sunlight received, influencing both APAR and overall productivity.

Environmental Considerations

• Cloud cover impacts APAR; areas with more clouds receive less sunlight, reducing potential productivity.

• Light use efficiency varies among plant species and depends on environmental conditions like soil fertility and water availability.

Utilizing Satellite Data

Understanding Net Primary Productivity

Estimating Productivity Across Different Areas

• The net primary productivity (NPP) of various regions on Earth can be estimated, with modeling used to compute both NPP and gross primary productivity (GPP).

• The Amazon rainforest is highlighted as one of the most productive areas, while the Sahara desert exhibits very low GPP due to limited plant life and water availability.

• Europe generally shows moderate productivity levels, whereas India and Southeast Asian nations have significantly higher GPP.

Factors Influencing Productivity

• Key factors affecting productivity include the solar constant, which is approximately 1388 watts per square meter, determining how much energy reaches Earth's surface.

• Variations in energy reception depend on geographical latitude, cloud cover, dust, and atmospheric moisture that can block photosynthetically active radiation.

Plant Adaptations for Maximizing Radiation Absorption

• The amount of sunlight received by plants is influenced by leaf area and arrangement; optimal leaf positioning enhances radiation interception.

• Other critical factors include atmospheric carbon dioxide levels and water availability in a given area.

Impact of Global Warming on Forest Dynamics

Modeling Carbon Sequestration Potential

• A simulation was conducted to assess global warming's impact on carbon sequestration potential in Chir Pine forests located in Almora district, Uttarakhand.

• Two main processes were examined: increased atmospheric CO2 levels leading to higher temperatures and their effects on plant growth.

Effects of Temperature Changes on Different Tree Species

• Increased CO2 may enhance glucose production through photosynthesis; however, temperature changes could either benefit or harm plants depending on their native conditions.

• For example, a banyan tree from tropical regions may thrive with rising temperatures in colder areas like Uttarakhand. Conversely, pine trees already stressed by warmth may suffer further under increased temperatures.

Data Collection for Productivity Analysis

Gathering Environmental Data

• Researchers collected data regarding precipitation patterns, temperature extremes, cloudiness levels in Almora district to analyze pine tree productivity.

Yield Tables as a Research Tool

Understanding Stand Volume and Carbon Sequestration

Relationship Between Plant Height, Diameter, and Volume

• As the height of pine trees increases, both the number of plants and their diameter decrease. This results in an increase in the total wood volume per hectare.

• The stand volume is measured as cubic meters of wood per hectare, with saplings contributing minimally at zero age. As trees mature, their timber volume increases significantly.

Model Calibration and Field Data Comparison

• A model is calibrated to reflect actual field data up to around 110 years of tree age, showing a strong correspondence between predicted values and observed data.

• The model also predicts a decline in plant numbers due to competition among trees leading to mortality over time.

Impact of Global Warming on Stand Volume

• Increasing carbon dioxide concentrations (from 360 ppm to higher levels) positively affect stand volume when temperatures are held constant.

• Conversely, increasing temperatures while keeping carbon dioxide constant leads to a decrease in stand volume.

Combined Effects of Temperature and Carbon Dioxide

• When both carbon dioxide levels rise (fertilization effect) and temperatures increase (harmful), the overall impact on stand volume can still show an increase under certain conditions.

• Modeling equations help predict outcomes based on different scenarios regarding carbon dioxide concentration and temperature changes.

Carbon Sequestration Dynamics Over Time

• The mean annual increment shows that carbon sequestration initially rises with tree age but eventually declines as older trees die off and decompose.

• Optimal management for maximum carbon sequestration suggests cutting trees at around 105 years; however, global warming may necessitate earlier cuts at about 70 years.

Nutrient Requirements for Forest Productivity

• Productive areas must provide essential nutrients like water, carbon dioxide, nitrogen, phosphorus, and potassium for plant growth.

Understanding Lake Trophic States

Oligotrophic Lakes

• Oligotrophic lakes are characterized by low nutrient content, often resulting from glacial meltwater, which is primarily composed of pure water with minimal mineral salts.

• The low levels of nitrogen, phosphorus, potassium, and calcium in oligotrophic lakes limit plant growth and primary productivity, leading to clear waters with high drinking water quality.

• An example of an oligotrophic lake is Tso Moriri in Ladakh, where minimal algae or plant growth is observed due to its glacial water source.

Mesotrophic Lakes

• Mesotrophic lakes represent an intermediate level of productivity between oligotrophic and eutrophic states. They typically have clearer waters and moderate nutrient levels.

Eutrophic Lakes

• Eutrophic lakes are defined by high biological productivity due to excessive nutrients, particularly nitrogen and phosphorus. This often results from agricultural runoff containing fertilizers.

• Increased nutrient concentrations lead to significant plant growth in eutrophic lakes compared to oligotrophic ones.

Hyper-eutrophic Lakes

• Hyper-eutrophic lakes exhibit extremely high nutrient levels that cause frequent algal blooms. These blooms can create nuisance conditions with low transparency and oxygen levels.

• The decomposition of dead plant material contributes to low oxygen levels in hyper-eutrophic lakes, creating "dead zones" that cannot support animal life.

Trophic Index and Secchi Depth

• The trophic index measures the productivity level across different lake types: increasing from oligotrophic through mesotrophic to eutrophic and hyper-eutropic states.

• Chlorophyll concentration increases with higher trophic states due to more abundant plants; phosphorus levels also rise significantly.

• Secchi depth indicates water turbidity; a greater depth signifies clearer water. It is measured using a disk lowered into the water until visibility diminishes.

Measuring Turbidity

• A secchi disk has black-and-white sections used for measuring clarity; as turbidity increases, the depth at which these colors can be distinguished decreases.

Nutrient Sources in Lakes and Oceans

Understanding Nutrient Levels in Different Lakes

• The depth of lakes varies significantly, with oligotrophic lakes averaging around 4 meters, while hyper-eutrophic lakes can be as shallow as 25 centimeters. This variation impacts nutrient availability and productivity.

Sources of Nutrients

• Rivers contribute nutrients by transporting sediments that contain mineral salts from rocks. As these rocks break down into sediments, they carry essential minerals into the water bodies.

• Bird droppings serve as another nutrient source. Birds feeding on fish absorb some nutrients during digestion but excrete a portion, including nitrogen-rich uric acid, which enriches the surrounding environment.

• Upwelling in oceans is a critical process where denser, nutrient-rich water rises to the surface due to various factors. This brings previously unavailable nutrients to the photic zone where plants can utilize them.

• Dust carried by winds also contributes nutrients to oceans. For example, dust from Africa can transport significant amounts of nutrients when deposited into marine environments.

Impact of Phosphorus on Lake Productivity

• A correlation exists between phosphorus concentration and chlorophyll levels in lakes; increased phosphorus leads to higher chlorophyll-a concentrations, indicating that phosphorus is often a limiting nutrient for algal growth.

• An experiment demonstrated that adding phosphorus (while keeping nitrogen constant) resulted in substantial algal blooms in one section of a divided lake, highlighting its role in enhancing lake productivity.

Iron's Role in Ocean Productivity

• In oceans, iron is typically scarce but crucial for primary productivity. The Southern Ocean Iron Release Experiments (SOIREE) showed that adding iron salts led to increased chlorophyll levels and enhanced phytoplankton growth.

Engineering Ecosystems for Carbon Sequestration

• Increasing primary productivity through iron seeding could help mitigate global warming by enhancing carbon sequestration via phytoplankton uptake of CO2 from the atmosphere.

Summary of Key Concepts