Primary Production, Food Webs, and Energy Flow

Question 1

What is the difference between plant production and plant biomass?

Answer 1

The biomass includes the mass of all living and dead organic matter. Production is the incremental increase in biomass produced by the plants

Question 2

What is Gross Primary Production (GPP)?

Answer 2

total carbon produced by primary producers (total energy fixed by autotrophs)

Question 3

What is Net Primary Production (NPP)?

Answer 3

carbon accumulated (in stored form) by primary producers (i.e. what is left over after respiration)

Question 4

What is Net Ecosystem Production (NEP)?

Answer 4

NEP = GPP – (AR + HR) 
AR = autotrophic respiration
HR = heterotrophic respiration

Question 5

What is the spinning wheel hypothesis?

Answer 5

The rate of production set by recycling of nutrients through zooplankton grazing

Zooplankton eats phytoplankton and releases Nitrogen. Phytoplankton take up recycled Nitrogen that is Supplied by Zooplankton. P and Z are tightly coupled. Standing stock biomass doesn’t have a chance to accumulate (but still productive!)

Question 6

What are the controls of GPP?

Answer 6

Climate (nutrients, light, H20 mixing)
Leaf Area Index (LAI) – leaf area per unit of ground area
*For each additional leaf layer, CO2 uptake starts to diminish

Question 7

What is the critical depth?

Answer 7

the place in the water where integrated P = integrated R

Question 8

What is the compensation depth?

Answer 8

P=R

Question 9

How does water column stability change with season, and what is the effect of this on aquatic primary production?

Answer 9

Early in the season, mixed layer depth is below the critical depth and causes a net destruction of biomass, primary production is low (less light, more wind). As the season progresses, the mixed layer depth is above the critical depth and biomass is much greater, primary production is high (more light, less wind)

Question 10

How do you calculate Gross Growth efficiency?

Answer 10

Carbon produced/Carbon consumed

Question 11

How do you calculate Assimilation efficiency?

Answer 11

Carbon assimilated/Carbon consumed

Question 12

How do you calculate Net Growth efficiency?

Answer 12

Carbon produced/Carbon assimilated

Question 13

What is allocthonous?

Answer 13

production of organic matter derived outside of the source

Question 14

What is autocthonous?

Answer 14

production of organic matter derived from within the source