Your Name:EEMB/ES 171-Winter 2015 Quiz # 2 Read each question carefullyUse the back if you need to1. (10). What are extracellular enzymes and why are they important in C-cycling?Enzymes released by decomposing microorganisms that cut plant polymers into pieces smallenough for microorganisms to take up. 2. (10). Describe at least two things that denitrification does that are important in theenvironment. 1. Remove NO3- from the system—this is bad if it’s fertilizer being lost, but good if it’s a wastetreatment plant. 2. Produce N2O, a potent greenhouse gas and ozone deplete. 3. Recycle N2 to the atmosphere. 3. (10). According to the Schimel and Bennett paper (Nitrogen Mineralization: challenges of a changing paradigm), mineralization is the critical process in driving overall cycling of N between organic and inorganic forms. True/False; if false why?False: that paper argues that depolymerization is the key process. It’s what converts polymeric materials that cannot be directly taken up by plants (e.g. protein) into forms that plants can potentially access.Your Name:4. (15) For each of the following plant traits, note whether it is likely to be higher or lower inplants growing in environments that are high vs. low in nutrients. Very briefly note why. Root/Shoot ratio:High Nuts: Low root/shoot ratio. When soil nutrients are plentiful, plants don’t need as muchroot biomass to access them. Leaf lifespan:High Nuts: Low lifespan. Leaves will have high nutrient concentrations to maximize photosynthesis. That will make them vulnerable to herbivores and environmental stressors. Polyphenolic compounds:High Nuts: Low polyphenols. Polyphenols are defensive chemicals and are part of what allows aplant to have a high leaf lifespan. But when plants are going for maximal activity (as they can when there are enough nutrients) then they don’t need high concentrations of polyphenols. 5. (15) Santa Barbara has a Mediterranean climate: rain ends by April and doesn’t start again until October. This selects for plants that have small, thick, waxy, evergreen leaves. A. (8) Why does this climate select for these leaves? Plants have to survive the hot dry summer. So they need to limit water loss—that means thickand waxy leaves. Also, because plant photosynthesis is constrained, small leaves are part of the picture. The leaves are adapted to surviving harsh conditions. B. (7) Do you expect this litter to decompose readily? Why or why not? No. Thick, waxy, low nutrient leaves are all things that make decomposition slow.Your Name:6. (12) A few years ago, I planted potatoes in my garden. The soil is a heavy clay. To improve the ground, I dug out the clay and replaced it with good topsoil, garden compost, and lots of manure. I also added bone and blood meals (for extra N and P). The potato plants came up large, green, and healthy. When I harvested the potatoes, however, thecrop was disappointing. There were few potatoes and those that were there were small. There was no evidence of pathogens. Why did this happen?I ensured that the plants had a very good supply of N. Thus, the plants used all that N to grow leaves, rather than sending it belowground to make roots—and potatoes. 7. (14) You have samples of the following two soils and you put them next to each other with a semi-permeable membrane between them. Soil A m = -0.8 MPa s = -0.5 MPaSoil B m = -0.1 MPa s = -1.1 MPaA. (7) Which way does water flow? Why?So the total water potential on each side is: m + s. The membrane only allows water to move and it will move from the most positive water potential to the most negative.Soil A water = -0.8 + -0.5 = -1.3 MPaSoil B water = -0.1 + -1.1 = -1.2 MPaWater will therefore flow from soil B to soil A. B. (7) The water content of each soil is 0.5 g H2O/g dry soil. Which soil is the finer texture? Why do you say so?The soils are the same moisture content, but soil A has a lower water potential, so it must hold onto that water more strongly—i.e. it has a finer texture.Your Name:8. (14) You are studying the breakdown of oil in oil. In a sample you find the following three molecules (along with a lot of others). A. (7) Which k value (decomposition constant) would you expect to go with each molecule? Why?K value Molecule? -0.01 Mol. C -0.05 Mol. A -0.1 Mol. BNote: more negative means faster decomposition. Molecule A is a long chain with few chemical functional groups (or “handles”) to make it easy to react, but nothing particularly challenging for a microbe to process. Molecule B is small, and has several functional groups (-OH group, double bond, amide group at the end) that make it more reactive. Molecule C is three condensed aromatic rings with no side chains. Nasty. Thus, molecule B should break down fastest and Molecule C slowest. B. (7) Consider that you add each of the purified compounds to soil. Which would you expect to mineralize N? Which would immobilize N? Why?The only molecule with any N in it is B. Thus, only B can mineralize N! Both of the others are only carbon and hydrogen. They cannot mineralize N they don’t have, but as microbes metabolize them, they will need to immobilize N to