Soil organisms, such as mycorrhizal fungt 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 tungl 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