Question

1. [12 pts] A team of scientists grew groups of birch trees in greenhouses under four conditions. "n.s." means not significant. a) The top graph shows total photosynthesis over a spring and summer. If the observed pattern occurs in the field as well (that is, not just in greenhouses) would the consequence be a positive feedback or negative feedback on climate change? (State your answer and explain in 3 sentences or less.) b) The bottom graph, from the same experiment, documents the date the trees dropped their leaves in the Autumn. Does the effect documented in the graph tend to strengthen or weaken the feedback you identified in Part (a)? (State your answer and explain in 3 sentences or less.) c) The scientists were puzzled that warming + CO2 had no greater effect than CO2 alone. Their hypothesis is that the amount of CO2 a birch tree can absorb over spring and summer is being limited by nitrogen. If you were to run your own version of the experiment to test the nitrogen-limitation hypothesis, what treatment groups would you add? (State your answer and explain in 3 sentences or less.)

          1. [12 pts] A team of scientists grew groups of birch trees in greenhouses under four conditions. "n.s." means not significant.
a) The top graph shows total photosynthesis over a spring and summer. If the observed pattern occurs in the field as well (that is, not just in greenhouses) would the consequence be a positive feedback or negative feedback on climate change? (State your answer and explain in 3 sentences or less.)

b) The bottom graph, from the same experiment, documents the date the trees dropped their leaves in the Autumn. Does the effect documented in the graph tend to strengthen or weaken the feedback you identified in Part (a)? (State your answer and explain in 3 sentences or less.)

c) The scientists were puzzled that warming + CO2 had no greater effect than CO2 alone. Their hypothesis is that the amount of CO2 a birch tree can absorb over spring and summer is being limited by nitrogen. If you were to run your own version of the experiment to test the nitrogen-limitation hypothesis, what treatment groups would you add? (State your answer and explain in 3 sentences or less.)

1. [12 pts] A team of scientists grew groups of birch trees in greenhouses under four conditions. "n.s." means not significant.
a) The top graph shows total photosynthesis over a spring and summer. If the observed pattern occurs in the field as well (that is, not just in greenhouses) would the consequence be a positive feedback or negative feedback on climate change? (State your answer and explain in 3 sentences or less.)

b) The bottom graph, from the same experiment, documents the date the trees dropped their leaves in the Autumn. Does the effect documented in the graph tend to strengthen or weaken the feedback you identified in Part (a)? (State your answer and explain in 3 sentences or less.)

c) The scientists were puzzled that warming + CO2 had no greater effect than CO2 alone. Their hypothesis is that the amount of CO2 a birch tree can absorb over spring and summer is being limited by nitrogen. If you were to run your own version of the experiment to test the nitrogen-limitation hypothesis, what treatment groups would you add? (State your answer and explain in 3 sentences or less.)

Added by Carol C.

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