Practice question

Deserts generally have the lowest primary productivity among the terrestrial ecosystems listed because water availability sharply limits photosynthesis, leaf area, and the length of active growth. Rainfall is sparse and unpredictable, and evaporation may exceed precipitation. Plants often remain widely spaced and invest resources in water storage, conservative metabolism, or extensive roots rather than continuous rapid growth. Productivity can surge briefly after rain, but annual net primary production remains low. Forests maintain much larger leaf area and biomass where temperature and water permit; grasslands receive enough seasonal moisture to support a continuous herb layer; and wetlands often achieve high productivity because water and nutrients are available, although nutrient-poor bogs are exceptions. Tundra can rival or fall below some deserts, but it is not among these choices. “Least productive” also depends on measurement: productivity per unit area differs from total global production, and some coastal deserts receive fog that supports local growth. Under the standard biome comparison intended here, chronic aridity makes desert the strongest match for low ecosystem productivity.