Plant Nutrient uptake (chpt 8, mostly), edited 3/19/14
Some topics NOT covered in exam 2 from chpt 7:
7-1 What is involved in anaerobic respiration? What are the materials used to ‘breath’ in
the absence of oxygen? Why are some substrates ‘preferred’ over others? (i.e., why does
the nitrate always get used first?).
7-2 What products of anaerobic decomposition provide ‘food’ (energy) for other
microbes that live in anaerobic environments?
7-3. Why is anaerobic decomposition a climate change concern?
1. Name at least four separate ways that plants can go about obtaining nutrients.
a) What’s the difference between mass flow and diffusion uptake? Where does
active transport fit into this?
b) How can hydraulic lift provide more nutrients than simple mass flow?
2. What is the risk of:
a) using exoenzymes to obtain nutrients?
b) using carbon compounds (CHO) to obtain nutrients?
2b. name an exoenzyme that both plants and microbes use.
3. Why are mycorrhizae likely to be better at obtaining nutrients per gram of tissue than
plant roots (per gram of tissue).
3b. The cycling of nutrients into plants from the soil can involve an almost totally closed
organic loop. Why is that important...and in what ecosystems would it be really
important?
4. How do we know that water or water+nutrients limit about half of the planet’s
terrestrial surface? How can we prove that a local ecosystem’s NPP is nutrient limited?
5. Explain two different ways that root exudates (the release of CHO compounds into the
rhizosphere) may INCREASE nutrient uptake by roots.
6..What are the forms of nitrogen (there are 3) that plants can uptake into their roots.
Which of these are “best”? Why does taking up nitrogen in one form rather than another
matter? (from chpt 9, but a good question!)
7..What’s the difference between an ‘essential nutrient’ and a ‘limiting nutrient’?
8. What nutrients drip from the canopy in throughfall? Which essential element in
particular appears to be ‘leachable’?
9. What is hydraulic lift (text, pgs 108-09), and why could it be important for nutrient
uptake?
Questions from text, chpt 8:
1. What is the rhizosphere? How do plants influence the rhizosphere?
2. How does plant growth rate affect nutrient uptake?
3. What are the major mechanisms by which mycorrhizae increase nutrient uptake by
plants? Under what circumstances are mycorrhizae most strongly developed?
4. Why do all aquatic and terrestrial plants tend to show a similar balance of nutrients (the
Redfield ratio)? How can you use this information to guess which nutrient (e.g., N or P)
is most strongly limiting to plants in a particular site?
5. What are the major differences in types of species that occur on fertile vs. infertile soils?
(think foliage traits).
6. What are the major avenues of nutrient loss from plants? How do all plants minimize this
nutrient loss? What additional adaptations minimize nutrient loss from plants that are
adapted to infertile soils?
7. A fairly ‘new finding’ in ecosystem ecology is the large amount of NPP that is exuded
into the soil (soil exudates). Our author depicts this in figure 7.9. Explain how in doing
this the plants “couple” rates of NPP to rates of decomposition and N mineralization? (a
truly great essay question!)