Soil organisms, such as mycorrhizal fungi, impact the rate of succession in ecosystems. Mycorrhizal fungi have a mutualistic relationship with various species of plants and increase the plant growth and survival. Sand dunes often lack mycorrhizal fungi, and a researcher wanted to determine the effect of adding mycorrhizal species to sand on disturbed beaches on grass growth. The researcher set up various mycorrhizal communities at disturbed beaches in different locations on the east coast of the United States. Identify the independent variable in the study.

The amount (number) of mycorrhizal fungi

Explanation:

In a scientific experiment/study, the independent variable is the variable that isn't changed by other variables, while the dependent variable is the variable that is being measured during the experimental procedure. The independent variable is manipulated by the researcher (in this case, the amount of mycorrhizal fungi), thereby affecting the dependent variable (in this case, grass growth). In consequence, a variable is dependent because it 'depends' on the independent variable.

this protocol provides a detailed procedure for co-immunoprecipitation (co-ip) to identify protein–protein interactions.