Net Primary Productivity

ECCB Exam 3

Primary production

The storage of energy through the formation of organic matter from inorganic carbon compounds.

Primary production

Carried out by autotrophic organisms.

Autotrophic organisms

Convert energy from sunlight into organic matter through primary production.

Autos (Greek)

self

trophikos (Greek)

related to food or nourishment

Autotrophs

"self-feeders" - producing the food needed for metabolisms, growth, and reproduction.

Photosynthesis

The light-driven process of carbon uptake and assimilation in green plants.

Light-use efficiency

Only 3-6% of absorbed light is converted into chemical energy by leaves.

Light reaction

The initial stage of photosynthesis

Light reaction

Light energy is absorbed by chlorophyll (in the thylakoid membrane).

Light reaction

Energy is converted into chemical energy (ATP and NADPH).

Light reaction

Oxygen is released as a byproduct.

Calvin Cycle

The second stage of photosynthesis

Calvin Cycle

Light-dependent reaction

Calvin Cycle

Carbon-fixation: Carbon dioxide from the atmosphere is converted into sugar molecules (glucose) using energy from ATP and NADPH.

Calvin Cycle

It occurs in the stroma of the chloroplast.

Photorespiration

Process in plants where the enzyme RiBisCO binds to oxygen (O2) instead of carbon dioxide (CO2) during the Calvin cycle.

Respiration

The process by which living organisms generate energy needed for life.

Respiration

Breaks down glucose in the presence of oxygen.

Respiration

1 glucose molecule yields 38 ATP.

Gross Photosynthesis

Total CO2 uptake by the leaf during photosynthesis (light-dependent reactions).

Respiration

CO2 released from the leaf as it breaks down carbohydrates (occurs both day and night)

Net Photosynthesis

Net CO2 gain by the leaf: Net photosynthesis = Gross Photosynthesis - Respiration.

NPP

Net Primary Production, calculated as NPP = GPP - Ra (Autotrophic Respiration).

GPP

Gross Primary Production, the total amount of CO2 fixed into organic compounds over a period of time.

Primary Production

The amount of organic compound a primary producer creates in a given length of time.

Biomass

Total mass of plant material at a point in time, expressed as mass per area or volume independent of time.

Gross Primary Production (GPP)

All CO2 is fixed into organic compounds over a period of time, measured in units of mass/area/time.

Net Primary Production (NPP)

The rate at which organic matter is available for uses beyond supporting energy costs of the primary producers.

Ecosystem Respiration (R_e)

All the respiration in the ecosystem, the sum of autotrophic respiration and heterotrophic respiration.

Net Ecosystem Production (NEP)

The amount of carbon that an ecosystem accumulates or releases over time, defined as NEP = GPP - Ra - Rh.

Organic Carbon Accumulation (dC_org)

The net deposition and storage of organic carbon in an ecosystem, influenced by NEP.

Carbon Allocation

Where a plant puts the photosynthate (carbon), influenced by stress and nutrient availability.

Forest Biomass

The total dry mass of living organisms and dead organic matter in a forest, measured per unit area (tons/ha).

Units of Primary Production

Measured in mass/area/time = (flux/rate) gC/m²/d.

Units of Biomass

Expressed as mass/area = (pool/stock - store of carbon or energy) gC/m².

Units of GPP

Measured in mass/area/time = (flux/rate) gC/m²/d.

Units of NPP

Measured in mass/area/time = (flux/rate) gC/m²/d.

Units of Ecosystem Respiration

Measured in mass/area/time = (flux/rate) gC/m²/d.

Units of NEP

Measured in mass/area/time = (flux/rate) gC/m²/d.

Units of Organic Carbon Accumulation

Measured in mass/area/time = (flux/rate) gC/m²/d.

Carbon Allocation Shift

A decrease in wood production is often an early sign of tree stress, as trees reallocate carbon to urgent functions.

Nutrient Availability Influence

In nutrient-rich environments, plants invest less in roots and more in leaves and wood to maximize growth.

Overstory

Tall canopy trees that dominate the upper layer.

Understory

Smaller trees, shrubs, and young trees growing under the canopy.

Forest Floor

Leaves, twigs, and partially decomposed material (O horizon).

Snags

Standing dead trees.

Coarse woody debris

Fallen logs and large branches.

Soil organic matter

Decomposed carbon stored in soil, supporting microbial life.

Human appropriation of NPP

According to NASA Goddard Space Center, human appropriation of NPP has increased from ~20% to ~25%.

Main uses of NPP by Humans

Crops for wood and fiber, timber for wood products and paper, livestock grazing.

Usable NPP Limit

The ceiling is usable NPP is NOT 100% - ecosystems require much of it to function.

Maximum sustainable threshold

Estimates suggest 33-40% might be the maximum sustainable threshold.

Net Primary Production (NPP)

NPP is strongly linked to climate pattern.

Regulation of primary production

Several factors are important in controlling primary production, particularly light, temperature, nutrients, water, and herbivory.

Photosynthesis and light

Photosynthesis depends on light; primary production tends to increase with increasing light up to a maximum.

Growing seasons

Shorter growing seasons on northern biomes (tundra and boreal) result in lower productivity.

Nutrient limitation

Primary production is nutrient-limited in most ecosystems.

Macronutrients

Essential nutrients such as N, P, O, H, S, K.

Micronutrients

Essential nutrients such as Fe, Mn, Zn, Cu.

Water and primary production

Terrestrial primary production is correlated with precipitation in broad comparisons among ecosystems.

Temperature influence

Terrestrial primary production is influenced by the temperature; higher temperatures generally increase photosynthesis, leading to higher NPP.

Complex limitations

The effects of these limitations on primary production are complex and depend on multiple interacting factors.

Single factor limitations

Single factor limitation of productivity is too simplistic; organisms can use one resource to gain another.

Most productive ecosystems

Tropical forests - warm, lots of light, enough water, tight nutrient cycling.

Least productive ecosystems

Deserts & Shrublands (low moisture, low nutrients); Tundra (very short growing season).

Photosynthesis role

Photosynthesis is the foundation of primary production - converting sunlight into usable energy.

NPP definition

NPP is what remains for growth and energy flow after respiration - it drives forest productivity and biomass accumulation.

Dynamic carbon allocation

Forests allocate carbon dynamically by environmental factors - light, temperature, water, nutrients, and biotic interactions.

Forest management

Understanding these processes helps us manage forests for carbon storage, biodiversity, and resilience.