To test how predicted increases in nitrogen deposition might
affect a temperate grassland ecosystem, researchers set up the
following experiment: over a 1-year period, experimental plots were
fertilized with excess nitrogen while control plots remained
unmanipulated. At the end of the experiment, they measured
aboveground biomass (an index of NPP; P = 0.033) and plant
species diversity (P = 0.005):

A. What is/are the independent and dependent variable(s) in this
study?

B. What are the two main conclusions you can draw from these
data?

C. Observed patterns in average NPP were likely due to what
biological processes? Explain.

D. Observed patterns in plant species diversity were likely due
to what biological processes?