Answers to Review Questions

1. Primary production is the source of the energy entering an ecosystem, and it therefore determines the amount of energy available to support that ecosystem. Primary production also results in the exchange of carbon between the atmosphere and the biosphere and thus is important in determining the atmospheric concentration of CO₂, an important greenhouse gas.

2. As NPP increased in a terrestrial ecosystem, the leaf area index would increase along with overall plant biomass. The amount of shading would increase as the leaf area index increased, and light would become increasingly limiting to growth. To compensate, plants would allocate more energy to stems and less to roots so as to increase their height and overtop neighbors in order to acquire more light.

3. The researchers found a correlation between NPP and soil temperature, and they assumed that the causal link was through the effect of soil temperature on root growth. While this assumption may be correct, the researchers failed to show the causal link conclusively, which would require careful experimentation, or at least more thorough measurements of the effect of soil temperature on the factors that can influence plant growth. For example, soil temperature can affect the rate of decomposition of organic matter in the soil, and thus the availability of nutrients, which may influence growth rates.

4.

a. Harvest techniques are simple and don't require high-tech equipment. However, harvesting can be labor-intensive, may fail to account for production that is lost to herbivores or decomposition, and is impractical at large scales.

b. Remote sensing provides estimates of NPP at larger spatial scales and can be used at frequent intervals. However, remote sensing is expensive and requires handling of massive amounts of data. Because it is based on absorption of light by chlorophyll, remote sensing can potentially overestimate NPP if a plant canopy is physiologically inactive.