Your Name:EEMB/ES 171 Fall 2017 Quiz # 1 Read each question carefullyUse the back if you need toTrue or False: If false, briefly explain why. 1. (6) T/F: Cation exchange capacity is an important characteristic of both clays and organic matter.True2. (6) T/F: Soil texture and structure are effectively the same thing. False: texture is the proportion of sand/silt/clay particles. Structure is how those particles are packaged in the “macro-structure” of the soil. 3. (6) T/F: The main resource limiting the productivity of tropical rainforests is typically nitrogen, because the soils are so old and weathered. False. The main resource limiting in old soils is typically phosphorus.Your Name:4. (12) If you were considering buying a piece of property to farm, the first piece of information you should probably check is the soils map. Why? Give at least three specifics.A soils map would tell you:1. Nutrient status2. Water holding dynamics3. Soil depth4. Are there hard pans that would be a problem for roots5. (10). What is the difference between photosynthesis and net primary production? Photosynthesis is the total amount of CO2 fixed by a plant. It pays no attention to plant respiration. NPP is equal to GPP (i.e. photosynthesis) minus plant respiration. It is the amount of C accumulated by a plant. 6. (16). You are doing a water balance on an area. The following values are for the summer only. PET = 1500 mmRainfall = 700 mmSoil water = 150 mm this amount of water is in the soil at the beginning of the summera) (5) What is AET for this summer? AET will either be equal to PET or to the amount of water available in the system. I.e. PET is thecredit card bill. AET is the amount you actually pay. If you have enough to cover the whole bill, you will. If you don’t, you’ll pay what you can. So: Available water is 850 (rainfall plus soil water). This is less than PET. Hence, AET = 850.b) (5) If all this rain comes in two big thunderstorms, would AET change? Why or why not?If all the rain came in two big storms it would almost certainly overwhelm the system’s ability to use all that water, and some would run off. Hence there would be less available for supporting plants. Less water would be used for AET, more would run off downstream. Consider two day-long storms. Seasonal PET is 1500. So, over a 100 day season, daily PET would be on the order of 15 mm/d. If each storm dropped 350 mm of rain in even a few days, thatwould overwhelm PET for those days.Your Name:c) (6) If the plants in this area had roots that went deep enough to reach groundwater, do you think AET would change? If so, how?If roots could reach groundwater, AET would increase because plants would use that water. 7. (16) Consider the ecosystem at right. You’ve established thefollowing measurements:1. A flux tower to measure the net ecosystem exchange of CO2 between the ecosystem and the atmosphere.2. Soil flux chambers to measure total soil respiration,which includes root respiration3. A flume on the stream to measure export.Assume there are no other important C fluxes.A. (8) What is the value for Net Primary Production?NPP is the C-gain by the plants via gas exchange. The whole system is gaining 10. But it islosing 4 to the atmosphere from soil respiration. So the gaseous exchanges are:Net C flux = NEENEE (10) = NPP – 4 = 14 g/m2yThe plants gain 14, the soils lose 4, the net change is 10. B. (8) What is the value for Net Ecosystem Productivity?NEP is the total net change in C stock in the ecosystem. That is inputs minus all outputs. NEP = 14 – 4 – 1 = 9 g/m2/yAlternatively NEP = Net gas exchange minus other C-losses. Hence: 10 – 1 = 9F l u x t o w e rN e t f l u x i n = 1 0 g C m y- 2 - 1S o i l r e s p i r a t i o n = 4 g C m y- 2 - 1S t r e a m e x p o r t = 1 g C m y- 2 - 1Your Name:8. (12) You set up a suite of fertilizer trials to test the fertility of a farm soil. You set up three plots in which you add either N, P, or a combination of both. Treatment Growth (kg)Control 9+N 9+P 14+N +P 18From these data, would you conclude that Liebig’s Law applies in this situation? Liebig’s Law says that only one resource may be limiting at a time. In this case, adding N alone does nothing for plant growth. Hence it is not independently limiting. Adding P alone does increase growth—hence it was limiting. Adding both increases growth beyond what P does on its own. So after you’ve eliminated the P-limitation, N is the next limiting nutrient. So adding N+P increases growth beyond what P alone will do. In this case, Liebig appears to work. 9. (16) You are evaluating the likely response of an ecosystem to climate warming. To do this, you measure how much the rate of each process increases as temperature increases. You measure the Q10 value which describes how much a reaction speeds up with each 10° C increase in temperature (a value of 2 means the rates doubles with a 10º C increase; so rate is 1 at10°, 2 at 20°, 4 at 30°, etc.).Process Q10Photosynthesis 2.0Plant respiration 3.0Soil respiration 1.5A. (8) As the temperature increases, will NPP increase or decrease? Why?Simple Answer: Plant respiration increases more rapidly with temperature than does photosynthesis. Hence NPP will decrease. Complex Answer: If you assume (as I’ve said is a common pattern) that GPP = 2 * NPPYour Name:Then consider: Temp Photo Resp NPP 10 2.00 1.00 1.0012 2.30 1.25 1.0514 2.64 1.55 1.0916 3.03 1.93 1.1018 3.48 2.41 1.0720 4.00 3.00 1.00At 10 C, photo = 2, Resp = 1 So: NPP = 1At 20 C, photo = 4, Resp = 3 So: NPP = 1At temperatures between these NPP actually goes up slightlyAt 30 C, photo = 4, Resp = 9 So: NPP = -5So above 20 C, NPP declines increasingly rapidly. No one needs to worry about this complex answer since no one did the math to work through what the patterns would look like if you made assumptions about the values of the individual pieces. B. (8) As temperature increases, will this system gain or lose carbon? Why?Here, there is no “complex answer.” At all temperatures, total C storage will decline. Even in the range from 10 to 20 C, where NPP might increase a little, and even if you only assume that soil respiration is equal to plant respiration, the slight increase in NPP will be more than compensated for by increased soil respiration and hence by C-losses. The “simple answer” is based on NPP declining as temperatures increase. Now add increased losses