Primary productivity is not limited by

Question

Primary productivity is not limited by 

Answer 1

I am assuming that this question is referencing Ecology, and focused on how much energy is produced by certain organisms in an ecosystem.

A basic definition of primary productivity is "the rate at which energy is converted to organic substances by photosynthetic and chemosynthetic producers" (Source: Britannica Encyclopedia; https://www.britannica.com/science/primary-productivity). Remember that basically, plants use sunlight energy and turn it into sugar, and chemosynthetic producers have a similar process but using various other chemicals.

Photosynthetic producers obtain energy and nutrients by harnessing sunlight (thus, the "photo" in their name), and chemosynthetic products obtain chemical energy through oxidation (the "chemo" in their name). An example of a photosynthetic producer is plants, an example of a chemosynthetic producer are some bacteria that live in the deep oceans, and obtain energy from chemicals such as sulfur, ammonia, iron, etc.

To be able to answer this question, which I am assuming is multiple choice, we need to understand how primary productivity is calculated. The productivity of these organisms is mostly based on carbon, so the equation is based on how much total carbon is created by the organism, and how much carbon is lost to respiration. The total amount of carbon that is created, in the form of sugar, refers to the Gross Primary Productivity (GPP), respiration is calculated as a loss, and the Net Primary Productivity (NPP) is what is left for the organism to utilize for its other internal processes. The basic equation is NPP = GPP - respiration.

In order to know what limits this process, we need to delve further into the actual productive processes of these organisms. For plants, this process is called photosynthesis. The chemical equation for this is: 6CO2 + 6 H2O ^(light) → C₆H₁₂O₆ + 6O₂. The factors that would limit this equation are the input of the equation, or the left side. These things would be carbon dioxide, water, and light.

For a chemosynthetic producer that utilizes hydrogen sulfide as a source of nutrients, which you may or may not have learned about, the chemical equation would be: CO₂ + 4H₂S + O₂ → CH₂O + 4S + 3H₂O. Again, the factors that would limit this would be the inputs on the left. In this case, that would be carbon dioxide, hydrogen sulfide, and oxygen.

So depending on the type of organism that you are discussing, the limiting factors might be slightly different. But in most cases, this question is focused on plants and algae as primary producers, so the photosynthesis equation is the right on to look at.

I hope this makes sense! Feel free to ask any further questions!