Ch. 20 Eco

21. Where is oceanic NPP the greatest? Why?

Oceanic NPP peaks at mid-latitudes, in zones of upwelling where nutrient-rich deep water comes to the surface.

6. How can a plant direct tissue growth to help it survive in a harsh environment? Other than growth, where might energy from NPP be allocated?

Allocation of NPP to storage products (e.g., starch) provides insurance against loss of tissue to herbivores, disturbances such as fire, and climatic events such as frost. Substantial amounts of NPP (up to 20%) may be allocated to defensive secondary compounds

10. How are chlorophyll concentrations measured, and how can these measurements be used to estimate NPP?

Estimate using remote sensing methods that rely on reflection of solar radiation. • Chlorophyll absorbs blue and red wavelengths and has a characteristic spectral signature.

25. What types of organisms are most associated with secondary productivity?

Most is associated with detritivores, primarily bacterial and fungi.

27. How were stable isotopes used to determine that vent invertebrates were not gaining their energy from the photic zone? Where do they get their energy instead?

Ratios of 13C/12C in vent invertebrates were different from phytoplankton in the photic zone. Therefore, their food source was not detritus from the upper ocean. symbiotic bacteria

24. Between terrestrial and aquatic systems, which has a higher proportion of NPP that becomes part of secondary production?

The fraction is greater in aquatic ecosystems than terrestrial.

22. Variation in NPP in terrestrial biomes is associated mostly with what two factors? What affects NPP variation most in aquatic ecosystems?

Variation in NPP in terrestrial biomes is associated mostly with leaf area index and length of growing season. Variation in NPP in aquatic ecosystems is primarily related to variation in nutrient inputs.

17. Why is NPP often low in rivers and streams? a. Where is most energy derived from? b. According to the river continuum concept, the importance of in-stream NPP increases with what? c. How do suspended sediment and nutrients affect NPP?

Water flow limits phytoplankton growth; most NPP is from macrophytes and attached algae. a. Most energy is derived from terrestrial organic matter. b. The river continuum concept describes the increasing importance of in-stream NPP as the river flows downstream. c. Suspended sediment in rivers can limit light penetration, thus water clarity often controls NPP. Nutrients, particularly N and P, can also limit NPP in streams and rivers.

26. What is chemosynthesis? Are these organisms heterotrophs or autotrophs?

bacteria use chemicals such as H2S, HS-, and S2- as electron donors to take up CO2 and convert it to carbohydrates chemoautotrophs.

3. What is a leaf area index (LAI)? a. When the LAI is below 1, what does this indicate? If the LAI is above 1, what does this indicate? b. If a higher LAI means more area to capture light and an increased photosynthetic rate, what limits the number of layers of leaves in a system?

leaf area per unit of ground area a. Less than 0.1 in Arctic tundra (less than 10% of the ground surface has leaf cover) b. Respiratory cost

11. What is NDVI, and how is it calculated? What does a high NDVI value indicate?

normalized difference vegetation index NDVI = (NIR - RED)/(NIR+ RED) High value = temperate and rainforest

4. Is all fixed carbon used to build tissue? Explain.

• Plants use about half of the carbon fixed in photosynthesis for cellular respiration. • Plants with a lot of nonphotosynthetic tissue (e.g., trees) have higher respiratory carbon losses. • Respiration rate increases with temperature, so tropical forests have higher respiratory losses.

1. What is the definition of an ecosystem based on energy flow?

Biotic + abiotic

20. Where are the highest rates of NPP on land found? Why?

Highest rates of NPP on land are found in the tropics Tropical zones have long growing seasons and high precipitation, promoting high rates of NPP

12. How are CO2 concentrations measured in a closed chamber used to estimate NPP? a. Where does this CO2 in this system come from? Is it just plants? b. What does this measurement give you? c. What must you do to calculate the NPP of the system?

Inside a tent or chamber, CO2 is added by respiration of plants and heterotrophs, including soil organisms. a. Uptake of CO2 is by photosynthesis. plants and heterotrophs, including soil organisms. b. The net change in CO2 is GPP minus total respiration: Net ecosystem production or exchange (NEE). c. Heterotrophic respiration must be subtracted from NEE to get NPP.

16. What limits NPP in lakes? How is it measured?

NPP in lakes is often limited by P and N availability NPP is measured as change in chlorophyll concentration or number of phytoplankton cells

9. How is NPP in a terrestrial ecosystem measured? a. Why is this only reasonable for aboveground NPP measurements? b. Why is this technique only useful for small plants in an area of low diversity? c. Why is it difficult to measure belowground NPP? d. What can be used to measure belowground NPP?

NPP is estimated by measuring increase in plant biomass in experimental plots and scaling up to the whole ecosystem a. This is a reasonable estimate of aboveground NPP if corrections are made for herbivory and mortality. c. Fine roots turn over more quickly than shoots—they die and are replaced quickly. • Roots may exude carbon into the soil or transfer it to mycorrhizal or bacterial symbionts. d. underground viewing tubes outfitted with video cameras • Allows direct observations of root growth, death • Helps in understanding belowground production processes

5. What is net primary productivity (NPP)? How is it different from gross primary productivity?

NPP is the amount of energy captured by autotrophs that results in an increase in biomass (living plant matter). • NPP is the energy left over for plant growth and for consumption by detritivores and/or herbivores.

8. Why is it important to understand NPP in a system?

NPP is the ultimate source of energy for all organisms in an ecosystem. Variation in NPP is an indication of ecosystem health. NPP is associated with the global carbon cycle.

7. Why does NPP vary with succession stage? During which stage is NPP that highest, and why?

NPP varies during succession, as LAI (ratio of photosynthetic to nonphotosynthetic tissue) and species composition all change. Highest NPP is usually during intermediate stages when plant diversity and nutrient supply tend to be highest.

14. What is the most important factor that affects NPP? a. How does NPP change with precipitation? Why? b. How does NPP change with increased annual temperature? Why? What happens to the net ecosystem exchange (NEE)?

NPP varies over space and time, mostly correlated with climate. a. NPP increases as precipitation increases, up to a point. b. NPP increases with average annual temperature. Ecosystem carbon storage (NEE) may not increase

13. What organism is responsible for most of the photosynthesis in aquatic habitats? a. Why don't harvest techniques work for this system?

Phytoplankton do most of the photosynthesis in aquatic habitats. a. Phytoplankton have short life spans • So biomass at any given time is low compared with NPP; harvest techniques are not used.

2. What is primary production? a. What types of organisms are primary producers? b. How is this energy stored? Why is this important for measuring primary productivity? c. What is gross primary productivity (GPP)? What does it depend on? d. What influences photosynthetic rate?

Primary production is the chemical energy generated by autotrophs during photosynthesis and chemosynthesis. a. Autotrophs b. stored as carbon compounds in plant tissues c. Gross primary production (GPP)—total amount of carbon fixed by autotrophs. • GPP depends on photosynthetic rate. d. Photosynthetic rate is influenced by climate and leaf area index (LAI)

23. What is secondary production? a. What are these organisms called? What are the four different types? b. How are stable isotopes used to determine an organism's diet? c. How do you calculate net secondary productivity? d. What does net secondary productivity depend on? e. How does secondary productivity differ between endotherms and ectotherms?

Secondary production: Energy derived from consuming organic compounds produced by other organisms. a. Heterotrophs: Herbivores, Carnivores, Detritivores, and Omnivores b. c. Ingestion - Respiration - Egestion d. - Quality of the heterotroph's food (digestibility and nutrient content) - Physiology. e. Animals with high respiration rates (endotherms) have less energy left over to allocate to growth.

15. What other factors can have an effect on the NPP of a system? a. Why might there be different responses to different climatic conditions between different areas of varying species composition? b. What controls NPP in terrestrial ecosystems? c. Why does the addition of water to a dry system not always increase the NPP of the system?

nutrient availability a. Different grass species have different growth responses to water availability. • There was a time lag in the response of the short- grass steppe to increased precipitation. b. Many experiments indicate that nutrients, particularly nitrogen, control NPP in terrestrial ecosystems. c. Soil moisture affects nutrient supply by influencing decomposition and nutrient dynamics.

19. In the open ocean, what is NPP mainly from? a. What is pico plankton? b. What else contributes to the NPP of the marine system? c. What is the main limiting nutrient in the open ocean? What is another one that may influence NPP?

variation in NPP is correlated with N inputs from rivers. a. Picoplankton (cells < 1 μm) contribute as much as 50% of the total marine NPP. b. Floating seaweeds such as Sargassum, kelp beds, and seagrasses also contribute to NPP c. In the open ocean, NPP is mostly N-limited. Iron