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University of North Carolina, GreensboroBIO 301Chapter 21 HW.
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4/17/2018 Chapter 21 HWChapter 21 HW
Due: 11:00am on Thursday, April 19, 2018
You will receive no credit for items you complete after the assignment is due. Grading Policy
Item 1
Ecosystems and the organisms that comprise them are dependent on nutrients, which are elements or compounds required for the growth and reproduction of
organisms. The loss of nutrients from an ecosystem is typically undesirable because it lowers ecosystem productivity and the diversity of organisms that can be
sustained by the ecosystem. Many human activities, such as logging and farming, have been correlated with increased nutrient loss.
The role that vegetation plays in preventing nutrient loss was studied in the Hubbard Brook Experimental Forest in New Hampshire in the late 1960s by Herbert
Bormann, Eugene Likens, and their colleagues.
Part A - Experimental observation: Nutrient cycling in a temperate forest ecosystem
Before manipulating any area of the Hubbard Brook Forest, the researchers spent several years studying the natural watersheds of the forest to try to
understand how nutrients move through the various living and nonliving components (reservoirs) of the ecosystem.
The diagram below depicts a simplified temperate forest nutrient cycle.
The yellow boxes show the main reservoirs of nutrients in the ecosystem.
The green arrows show the processes involved in the transfer of nutrients among the reservoirs.
Note that rainfall results in a net input of nutrients into the ecosystem, whereas erosion and leaching (the loss of soluble nutrients from the soil in
groundwater) represent a net loss of nutrients. In Hubbard Brook, as in most temperate forest ecosystems, the amount of nutrients gained and lost through
rainfall and erosion or leaching, respectively, is small compared to the total amount of nutrients moving around the cycle.
Drag the words or phrases on the left to the appropriate blanks on the right to complete the sentences. Use only pink labels (reservoirs) for pink
targets and blue labels (processes) for blue targets. Not all terms will be used.
Hint 1. What is the largest reservoir of nutrients in a temperate forest ecosystem?
Typically, compounds accumulate in specific reservoirs because the processes that remove nutrients from that reservoir are slow. The slowest
process limits the rate at which nutrients move through the cycle; therefore, it is called the rate-limiting step. The largest nutrient reservoir precedes
the rate-limiting step.
Which of the following is the largest nutrient reservoir in a temperate forest ecosystem?
ANSWER:
https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=6601706 1/19
,4/17/2018 Chapter 21 HW
inorganic nutrients in the soil
organic nutrients in the soil
consumers
plants
Hint 2. Through what process are nutrients lost from a temperate forest ecosystem?
Which process results in the largest loss of nutrients from a temperate forest ecosystem?
ANSWER:
death
decomposition
plant uptake
erosion or leaching
Hint 3. Difference between a reservoir and a process
A reservoir is a location in which a component of the nutrient cycle can be found. A reservoir may be living (such as plants, animals, or
decomposers) or nonliving (such as inorganic nutrients in the soil or dissolved in streams or groundwater).
A process, in contrast, is a mechanism that transfers nutrients among the reservoirs of a nutrient cycle. Processes may be accomplished by living
organisms (uptake by plants, consumption by animals, or decomposition by bacteria and fungi) or by physical and chemical phenomena (addition of
nutrients by rainfall or losses through erosion or leaching).
ANSWER:
Reset Help
organic nutrients
plants
inorganic nutrients
plant uptake
decomposition
erosion or leaching
https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=6601706 2/19
, 4/17/2018 Chapter 21 HW
Correct
The Hubbard Brook ecosystem is typical of most temperate forest ecosystems in that the majority of the ecosystem’s nutrients are contained in
the soil as organic nutrients. There are two major components of this organic nutrients reservoir: detritus and decomposers. Detritus consists of
dead and decaying organic matter derived from plants and animals. Decomposers are soil bacteria and fungi that break down the detritus,
ultimately contributing to the inorganic nutrient reservoir in the soil.
The decomposition of organic nutrients in the soil is usually the slowest process in the nutrient cycle of a temperate forest. Therefore,
decomposition can limit the overall productivity of the ecosystem.
While most of the nutrients in a temperate forest ecosystem cycle through the soil, plant, and animal reservoirs, some nutrients are completely
lost from the ecosystem through erosion or leaching of inorganic nutrients from the soil. These losses may be compensated for by the input of
nutrients in rainwater.
Part B - Experimental results: How devegetation affects the nutrient cycle
The Hubbard Brook Experimental Forest consists of several adjacent watersheds (regions of the forest drained by a single stream), all of which drain into
Hubbard Brook. In one of the watersheds, researchers cut down all of the trees and sprayed the entire watershed with herbicides to prevent any re-growth
of plants for a period of three years. The roots of trees and shrubs were not removed, and the above-ground parts of plants were left to decay. Other
watersheds were left untouched as controls.
Devegetation affected a number of nutrient reservoirs and processes in the experimental watershed. Note that the rate of decomposition was not affected
by devegetation because the decomposers were not affected by the treatments and because the plant remains contributed plenty of organic nutrients to the
soil to sustain decomposition for the duration of the experiment.
Drag the labels to indicate the change in the size of the reservoir or the change in the rate of the process as a result of devegetation. Labels may
be used once, more than once, or not at all.
Hint 1. How to approach the problem
1. Review the image of the undisturbed nutrient cycle (see below).
2. Now imagine the researchers cutting down all of the plants (devegetation).
3. Think about how devegetation would affect the process of plant uptake. Remember that only living plants can take up inorganic
nutrients from the soil.
4. Knowing what you do about the change in plant uptake, and that the rate of decomposition remains the same, think about how the size
of the inorganic nutrient reservoir in the soil would change. (For more help on this point, see Hint 2.)
5. Think about how the change in the size of the inorganic nutrient reservoir in the soil would affect the rate of erosion and leaching and
ultimately nutrient loss from the watershed.
https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=6601706 3/19
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