Chapter 20: Production Flashcards
When was the first use of the term ecosystem and what did it refer to?
-Tansley (1935)
-Refers to all the components of an ecological system that influence the flow of energy and elements
Ecosystem Concept
integrates ecology with other disciplines such as geochemistry, hydrology, and atmospheric science
Where does the energy in ecosystem originate?
autotrophs
Primary Production
chemical energy generated by autotrophs during photosynthesis and chemosynthesis
Source of Energy for all organisms
primary production
Where are fossil fuels derived from?
primary production
Where is energy assimilated from autotrophs stored?
carbon compounds in plant tissues
Primary Productivity
rate of primary production
Gross Primary Production (GPP)
total amount of carbon fixed by autotrophs
What is GPP controlled by?
-climate through its influence on photosynthetic rate
-Leaf area index: leaf area per unit of ground area
What is the variation in LAI among biomes?
-less than 0.1 in Arctic tundra (less than 10% of the ground surface has leaf cover)
-12 in boreal and tropical forests (12 layers of leaves between the canopy and the ground, on average)
What is the relationship between shading and photosynthesis?
-When shading increases, the incremental gain in photosynthesis for each added leaf layer decreases
-Eventually, the respiratory costs associated with adding leaf layers outweigh the photosynthetic benefits
How much fixed carbon do plants use in photosynthesis for cellular respiration?
about half
What type of plants have higher respiratory carbon losses?
plants with a lot of non-photosynthetic tissue (trees)
What increases with temperature?
respiratory rate
What biome has the higher respiratory losses?
tropical forests
Net Primary Production (NPP)
GPP-Respiration
NPP
-the amount of energy captured by autotrophs that results in an increases in biomass (living plant matter)
-the energy left over for plant growth and for consumption by detritivores and herbivores
How do plants respond to environmental conditions?
allocating carbon to the growth of different tissues
How does allocation of NPP to storage products affect the plant?
provides insurance against loss of tissue to herbivores, disturbances such as fire, and weather events such as frost
How much NPP may be allocated to defensive secondary compounds?
up to 20%
What varies during succession and why?
-NPP as LAI and species composition all change
When is NPP the highest?
usually during intermediate stages when plant diversity and nutrient supply tend to be highest
What happens to NPP and LAI in old growth forests?
-NPP may decline as LAI and photosynthetic rates decrease
-But Old-Growth ecosystems have large pools of stored carbon and nutrients for many animal species
-Decrease in NPP over time is less pronounced in grasslands than in forests
What is the ultimate source of energy of all organisms in an ecosystem?
NPP
What is an indication of ecosystem health?
variation in NPP
What is associated with the global carbon cycle?
NPP
Terrestrial Ecosystem
NPP is estimated by measuring increase in plant biomass in experimental plots and scaling up to the whole ecosystem
Harvest techniques for NPP
-measure biomass before and after growing season
-this is a reasonable estimate of aboveground NPP if corrections are made for herbivory and mortality
Why is measuring below ground NPP more difficult?
-fine roots turn over more quickly than shoots (they die and are replaced quickly)
-roots may exude carbon into the soil and transfer it to mycorrhizal or bacterial symbionts
-Harvests must be more frequent and additional correction factors are needed
What’s another way to measure below ground biomass other than harvest techniques?
it can be estimated from aboveground measurements and algorithms that relate above and belowground biomass
What are Minirhizotrons and why are they helpful?
-underground viewing tubes outfitted with video cameras
-allow researchers to directly observe root growth and death
-led to advances in understanding below ground production processes
When are harvest techniques impractical?
large or biologically diverse ecosystems
What can be used as a proxy for GPP and NPP?
chlorophyll concentrations
How can chlorophyll concentrations be used to estimate GPP and NPP?
estimate using remote sensing methods that rely on reflection of solar radiation
What wavelength colors do chlorophyll absorb?
blue and red and has a characteristic spectral signature
What wavelengths do plants reflect?
near infrared wavelengths
read slides 30-33
How is NPP measured from GPP and respiration measurements?
-change in CO2 concentration is measured in a closed chamber
-sometimes whole stands of plants are enclosed to study CO2 exchange
Net Ecosystem Exchange (NEE)
-GPP minus total respiration
-more refined estimate of ecosystem carbon storage than NPP
Eddy Correlation or Eddy Covariance
NEE is estimated by measuring CO2 at various heights in a plant canopy
How does a gradient of CO2 develop?
Because of photosynthesis and respiration
How does the time of day affect the CO2 concentration?
-during the day, CO2 decreases in the canopy with photosynthesis
-at night, CO2 is higher in the canopy
What is the network that measures the amount of carbon and climate conditions?
eddy covariance sites
What does most of the photosynthesis in aquatic habitats?
phytoplankton
Read slides 43-45
