Final answer:
Carbon becomes a limiting nutrient when it is in short supply for photosynthesis, which can occur due to a surge in plant growth or through human activities that upset the biogeochemical carbon cycle.
Step-by-step explanation:
Carbon would become a limiting nutrient in an ecosystem when it's not sufficiently available to meet the needs of organisms, particularly plants, that depend on it for photosynthesis. While nitrogen is more often the limiting factor in terrestrial ecosystems, carbon can become limiting if there is a significant decrease in the atmospheric levels of carbon dioxide, which could occur through various processes such as increased photosynthesis by a surge of plant growth, sequestration in oceans, or trapping in sediments. The biogeochemical cycles, such as the carbon cycle, illustrate the movement and transformation of carbon through different forms and reservoirs like the atmosphere, oceans, soil, and living organisms.
Human activities, such as burning fossil fuels and deforestation, have significantly altered the carbon cycle by increasing atmospheric carbon dioxide. This rapid increase in carbon may exceed the capacity of photosynthetic organisms to utilize it and can contribute to global climate change, which can influence the biogeochemical cycles and potentially lead to situations where carbon becomes a limiting nutrient.