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Q45 - Nitrogen and Phosphorus Accumulation Trajectories Through Primary Succession

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Ecology

Primary succession can begin in a virtually lifeless area, characterized by early-seral plant species followed by replacement with late-seral plant species, as seen in Alaska where glaciers have retreated during the Holocene. Nitrogen enters soil through biological nitrogen fixation (conversion of N2 into usable forms). Phosphorus is added to soil through weathering of rocks. After plant death, elements can reenter soil through microbial decomposition and mineralization, but some nutrients are lost through leaching. The climax stage is boreal forest.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

N and P accumulation pattern. Choose the panel that represents temporal changes in the total amount of nitrogen (N) and phosphorus (P) accumulation in soil through primary succession after glacial retreat in Alaska.
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Question reproduced from IBO 2020, Theoretical Exam 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)