Final answer:
At high densities, plant growth rates typically decrease due to increased competition for resources. While greater leaf area can facilitate faster growth, this is countered by resource limitations when plants are closely packed together.
Step-by-step explanation:
When experimental plants like Atriplex prostrata are grown at high densities, there can be a variety of impacts on individual plants and the population as a whole. However, given the context of the question, the most accurate response would be that individual growth rates tend to decrease. High plant density can lead to increased competition for resources such as light, water, and nutrients, which generally results in reduced growth rates per individual plant. This is due to the fact that plants can only increase photosynthetic surface area and biomass production up to a point before they start competing with each other, limiting the growth potential of each individual plant.
While it is true that plants with more leaf area generally grow faster because they can capture more energy for photosynthesis, this advantage diminishes when high density causes competition for light and nutrients. Studies have shown that traits like high specific leaf area, high leaf nitrogen content, and high photosynthetic capacity are not enough to counteract the effects of competition at high densities. Moreover, environmental factors, such as elevated levels of CO2, can influence growth, but the response varies with environmental conditions and species-specific traits.
The correct answer to the student's question is that typically, individual growth rates would not increase under high plant densities due to competition for resources, despite adaptations that might otherwise facilitate growth.