Productivity: Productivity is the amount of organic matter made by photosynthesizing (and/or sometimes chemosynthesizing) organisms in an ecosystem. In photosynthesizing organisms (e.g., plants, algae, and some bacteria) light energy from the Sun is converted into chemical energy and stored as organic matter, for example, in plants as wood, leaves, and roots. Chemosynthesizers use chemical reactions, often in the absence of light, to produce organic matter. Animals that eat photosynthesizing organisms (called herbivores), and animals that eat other animals (carnivores), get their energy for growth, reproduction, and other functions from their food through the process of cellular respiration, where the ingested food is converted to ATP.
Biomass is the mass of all living organisms in an ecosystem, or the mass of one or more species in an ecosystem, at a particular time.
Productivity and biomass in ecosystems are affected by many Earth system processes and phenomena, including:
- Evolutionary processes that can change the growth and reproduction rates of organisms over time.
- Species interactions, including how species provide resources for each other, consume each other for food, or compete for resources such as food, water, and/or space. Species that reduce or increase the success of other species alter population sizes, thus affecting productivity and biomass.
- Climatic conditions, such as the amount of sunlight absorbed at different latitudes, temperature, and precipitation For example, ecosystems at low latitudes, such as tropical rainforests, have higher productivity and biomass than ecosystems near the poles because of they receive more sunlight and rainfall than regions at higher latitudes.
- Nutrients, especially nitrogen and phosphorus, when limited, can decrease productivity, and when abundant can increase productivity and biomass.
- Numerous other abiotic environmental factors, including soil quality (often related to nutrient levels), wildfires, water acidity, and oxygen levels.
Humans have altered productivity and biomass in ecosystems through a variety of activities, including:
- Deforestation, habitat destruction, and urbanization, which remove organisms from the environment and disrupt ecosystems.
- Agricultural activities that increase the amount of livestock and crops available to feed the growing global human population.
- The use of fertilizers for agricultural activities that increase the amount of nutrients, especially nitrogen and phosphorous, in soil or water. These nutrients increase plant and algae growth, including growth of species that are toxic to other organisms. Increased nutrient is not always a good thing. For, example, in aquatic environments, nutrient-rich runoff can cause large amounts of algae grow – when these algae die, they are consumed by bacteria which can reduce oxygen levels in the water, killing fish and other species. This process is known as eutrophication.
- Fishing and hunting, which reduces species populations of the exploited species, but can also lead to increased numbers of other species. For example, in Yellowstone National Park, the elimination of wolves led to an increase in the elk population.
- Human freshwater use, which can limit the amount of water available for other organisms in an ecosystem.
- The release of pollutants and waste which can reduce growth and reproduction or kill organisms.
- Activities that cause global warming, such as the burning of fossil fuels, agricultural activities, and deforestation. Increasing average global land and ocean temperatures have altered temperature and precipitation patterns, as well as the distribution of snow and ice cover, which affects the growth and survival of some species.
- Activities such as the burning of fossil fuels, agricultural activities, and deforestation. that release carbon dioxide into the atmosphere, which is absorbed by the ocean causing acidification. The decreasing pH of ocean waters (along with ocean warming) causes physiological stress for many species, which can decrease growth, reproduction, species population sizes, and biomass.
- Introducing invasive species that compete with native species for food, water, or other resources, reducing native species populations.
Can you think of additional cause and effect relationships between biomass and productivity and other parts of the Earth system?
Visit the evolution, species interactions, and species population pages to explore more connections between the biosphere and global changes.
Learn more in these real-world examples, and challenge yourself to construct a model that explains the Earth system relationships.